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VRVision User Manual

1. Examples vrvis UseQuitKeys abcdef quit when keys A F pressed vrvis UseQuitKeys any quit when any key pressed vrvis UseQuitKeys 0 disable keyboard quit If the user quits by pressing a key it is possible to find out the elapsed time and the key that they pressed using the following two functions GetQuitKey GetQuitKeyTime UseMouseMove This function allows you to rotate the scene using the mouse If enabled horizontal movement of the mouse will rotate the scene about the Y axis azimuth and vertical movement will rotate the scene about the X axis elevation The range of movement on each axis can be specified in terms of a maximum angle For example specifying an angle of 45 degrees will allow the model to be rotated between 45 and 45 degrees You can lock a particular axis prevent rotation on that axis by specifying an angle limit of zero Examples vrvis UseMouseMove 1 A nable mouse movement vrvis UseMouseMove 0 disable mouse movement vrvis UseMouseMove 1 45 0 allow 45 rotation about X vrvis UseMouseMove 1 0 45 allow 45 rotation about Y vrvis UseMouseMove 1 15 15 allow 15 rotation about X Y Mouse rotation can be recorded to file and replayed later Please see the RecordToFile and PlayFromFile functions for further details UseJoyMove This function allows you to rotate the scene using a joystick or trackball Most devices that appear as a stan
2. vrvis SetFilename filename wrl vrvis SetFilename filename iv vrvis SetFilename samples robot iv Note the path separator is for example folder file iv SetModifier You can specify an optional modifier to the 3D scene The modifier is simply another Inventor VRML file that is loaded immediately before the 3D scene in technical terms the 3D scene becomes a child node of the modifier Therefore any Inventor nodes in this file will affect the scene This is mainly a convenience for the user since the same scene file can be loaded under a number of different modifiers to achieve different results This is a very powerful feature and has many possible applications e Animation For example to make a scene rotate automatically e Lighting For example to view the same scene with different lighting conditions e Resize Reposition Scale or translate the scene before display e Display styles For example to modify the draw style wireframe points etc It is probably simpler to explain this with an example 1 Create a text file called wire iv containing the following text Inventor V2 1 ascii DrawStyle style LINES You can use any text editor to do this notepad for example 2 Setup VRVision to use this as a modifier vrvis SetModifier wire iv 3 Now when you use VRVision normally to display a scene vrvis SetFilename yourscene iv
3. 0 disable stereo the default For more details about the hardware requirements for stereo support please refer to Section 7 UseHeadTrack This function enables head tracking if a suitable tracking system is first connected and properly configured When enabled the display is continuously updated to provide an appropriate view for the current head position of the viewer In particular if stereo mode is also enabled the left and right eye positions of the viewer are calculated and used to provide two different projections using an asymmetric viewing frustum Please refer to Section 9 for further details Examples vrvis UseHeadTrack 1 enable head tracking vrvis UseHeadTrack 0 disable head tracking UseTimeLimit Specifies a time limit in seconds after which the application will automatically close This can be used to display a particular 3D scene for a limited time period Examples vrvis UseTimeLimit 12 5 display for 12 5 seconds vrvis UseTimeLimit 0 disable the time limit UseQuitKeys This function allows you to specify which keys can be used to quit from the application When the application quits it will return to Matlab The default is to disable quit keys except for the ESC key which can always be used to quit You can specify a character string listing the acceptable quit keys or you can specify the special string any which will accept almost any key on the keyboard
4. Point Light The point light source emits light equally in all directions from a specific point For example imagine a soft light bulb floating in space The exact position of the light can be specified 13 Light Q The light source is defined in the Inventor iv file as follows PointLight 1 location 0 0 1 The location position of the light source is specified again by a vector consisting of three values These represent the X Y and Z co ordinates of the light source In the example above the light is located at one unit on the Z axis For our purposes this places our light one metre out from the centre of the screen Increasing the X component the first value would move the light to the right and increasing the Y component the second value would move the light up Spot Light The spot light has a particular position in space but also has a direction of illumination For a real world analogy consider a desk lamp with a shade This type of light projects light in a particular cone Q The light source is defined in the Inventor iv file as follows Light SpotLight location 0 0 1 direction 0 0 1 dropOffRate 0 cutOffAngle 0 785 The location position of the light source is specified again by a vector consisting of three values that represent the X Y and Z co ordinates of the light source see PointLight The direction vector specifies which direction th
5. and a point that lies halfway between the two eyes of the viewer In this case the receiver was mounted on the top of a pair of CrystalEyes glasses facing towards the transmitter and tilted backwards towards the forehead Therefore the direction vectors are used to account for this rotation on the X axis Since it is a simple X axis rotation you will notice that the X direction vector is unaffected in the example above As with the transmitter a position offset is also needed Sample Ascension Flock of Birds Here is a complete sample configuration for an Ascension Flock of Birds with a single receiver on COM1 Note that the rest of the INI file has been omitted for reasons of space and only the three sections that relate to the tracking system are shown here Tracker Device bird name of tracking system to use Port port 1 which COM port to use GlassPort 1 which port the glasses are on TrackerXForm X 1 0 0 direction vectors for transmitter Y20 0 1 Z 0 1 0 P 0 51 0 27 0 38 translation for transmitter GlassesXForm X 0 0 1 direction vectors for receiver Y 0 1 0 Z 1 0 0 P 0 0 0 07 translation for receiver The TrackerXForm specifies the transformation between the tracking system transmitter and the screen centre In this case the tracker X Y Z axes were aligned with the screen X Z Y axes respectively Therefore the X axis vector in the TrackerXForm is set to the X axis 1 0 0 the
6. is provided on the VRVision web site Although this section describes only the Open Inventor file format it is worth mentioning that the VRML file format is based on Open Inventor and is therefore very similar The Open Inventor library and VRVision can load VRMLI files but not VRML2 VRML97 files This is a limitation of the open source version of Open Inventor 2 1 It future it would be possible to recompile VRVision to work with the commercially available Open Inventor 3 1 or later which is sold by Template Graphics Software www tgs com and which does support VRML2 Alternatively the Coin3D library from Systems in Motion also supports VRML2 This is an Open Inventor work alike which is available under both open source and commercial licenses Example 1 Creating a Cube Open Inventor has built in support for a number of simple primitive objects such as cubes cylinders spheres and cones We can create a file that contains one or more of these objects very easily 18 Start by using a text editor to create a new text file Enter the text shown below being careful to copy it exactly as shown Inventor V2 1 ascii Cube Save this file as cube iv The iv file extension indicates that this is an Open Inventor file as does the first line of the file You may find that some text editors will not allow you to change the file extension and may automatically add the txt extension by default If this happens it may b
7. 9 2 Configuration File Settings There are three separate sections in the INI file that are used to configure the tracking system for use with VRVision Tracker tracker communication settings rackerXForm transform transmitter screen GlassesXForm transform receiver glasses These are documented in section 7 and briefly summarised here Sample Logitech 3D Mouse Here is a complete sample configuration for Logitech 3D Mouse on COMI Note that the rest of the INI file has been omitted for reasons of space and only the three sections that relate to the tracking system are shown here Tracker Device 3dmouse name of tracking system to use 35 Port port 1 which COM port to use or auto GlassPort 1 which port the glasses are on TrackerXForm X 1 0 0 direction vectors for transmitter Y 0 1 0 Z 0 0 1 P 0 0 466 0 295 translation for transmitter GlassesXForm X 1 0 0 direction vectors for receiver Y 0 0 89879 0 43837 Z 0 0 43837 0 89879 P 0 0 08 0 04 translation for receiver The TrackerXForm specifies the transformation between the tracking system transmitter and the screen centre In this case the transmitter was mounted centrally on top of a 19 flat screen monitor and the axes were aligned with the monitor Therefore only a position offset translation is needed in the example above The GlassesXForm specifies the transformation between the tracking system receiver
8. E EE ob RODEO DTI iD serie vtm I 35 9 1 Supported Tracking Systems rre TE DEP SVEDESE I DEED EE 35 9 2 Conhiguration leese 35 sample Logitech 3D MOUS Esn S nger 35 Sample Ascension Flock of pieds Seed E RE AEE 36 1 Introduction VRVision is a MEX plug in for Matlab which allows 3D scenes to be displayed in real time with controllable lighting perspective and photo texturing Scenes can be presented in true stereoscopic 3D and with a dynamic viewpoint that accounts for the head position of the viewer It directly supports VRML1 and OpenInventor file formats and other formats can be read by using third party file converters The software was originally designed for use by Psychologists in behavioural research experiments It was conceived as a replacement for databases of pre rendered 2D images that were typically prepared using packages such as 3D Studio MAX Discreet or Maya Alias Wavefront With VRVision it is possible to display 3D scenes in real time and to vary the conditions such as lighting orientation texturing animation during the course of an experiment This can be achieved without the need to generate large databases of images and can therefore save a lot of time and effort on the part of the researcher VRVision was designed for use with existing software such as Matlab and the Psych Toolbox which have become popular for this type of study 2 Requirements 2 1 Software Requirements The basic requiremen
9. LOU NI De EEUU MES 13 Direcional Bru EEUU 13 Joost oni Aea oi M r 13 Spot E E 14 Common Light Properties oce ter reete ret e re px OE EE HR e e E Re ere Rr dee 15 Material Properties C NEPR 15 Multiple Light SOUfGeS eerte ehe t e t tr erret b HERO or erp pir o E REPRE enee 16 B seColour Laghtmg ero redet tr ee ro reo ER REPAS UHR dere 16 Animated EE ee 17 622 Th Scene E E 17 Detault Scene Graph eere orte ertet rer ree e REPRE ODE See 17 ROtate First Sio M MM 18 6 3 The Open Inventor File Formal order tette pato repre te Feb m EEREN 18 Example 1 Creating a Cube cited I eror Rer ie erint EN ERE OR Prep 18 Example 2 Transtormations gedd 19 Example 3 Using Separ tors 5 ioco ora GrH Wisi EO eege e 20 Example 4 Complex SUrfaces io nti todos do ito potiiis 2 T Imtralisation D us rc neos in Ca nod tpi dettes t tepore prete 22 Tels Sct en EEN 22 7 2 Camera rr ione D ca adeb a t e P d Oe cr c c dee c dea 23 EE DR E dE 24 TA TrackerXFortn i reet rca nere te re c eer c ci dee c deeds 25 75 GlassesXFotm iiec te n e erectae e He cibi c code dee dg 26 E ET TEE 26 PEA ODA a E Em 29 S Hardware fot SIereoSCODy i cites tec ere ron pbi E ose Seen SRS 30 8 1 Display Devices EE 30 Shutter EE 30 eut 31 8 2 Graphics EE 31 The SD abs EE 32 The nVadia Quadro GeEorce Tat e 5 5 chee Bienes isto TE DATI Een 32 ET
10. Specifies the scene position as an X Y Z translation in metres If the AutoCentre option is enabled in the INI file this translation will be applied after the auto centre Therefore you can combine these two options However if you want to specify an absolute translation for the object in world coordinates you should ensure that AutoCentre is first disabled otherwise your translation will be made relative after the object has first been moved to the origin For example to move the object 1m behind the screen assuming that it is normally located at the origin vrvis SetScenePos 0 0 1 The origin 0 0 0 is the centre of the screen From the point of view of the user the X axis points right the Y axis up and the Z axis points out of the screen SetScale This function sets the scene scale factor This will be used in preference to the value given in the INI file For example to set an absolute scale of 1 10 normal size vrvis SetScale 0 1 The size on screen may be affected by the following e Object dimensions in the scene file e Screen size settings in the INI file e Scale factor either from INI file or the SetScale function e The viewer object position relative to the screen SetAngleX Applies a rotation about the X axis right axis given an angle in degrees The rotation angle can be positive or negative For example to rotate the scene by 45 degrees vrvis SetAngleX 45 This function is a
11. Up 0 1 0 Final notes If you are familiar with the use of field of view angles and aspect ratio settings for setting camera parameters it is worth noting that in the case of VRVision these are calculated on the basis of the screen dimensions and view position relative to the screen For example the aspect ratio is determined by dividing the screen width by the screen height 7 3 Tracker These settings are used to interface VRVision to an external tracking system to support the head tracking feature VRVision talks to this external hardware through a proprietary library called TrackLib In order to connect to a particular device TrackLib needs to know the device name the physical port that it is connected to for example COMI serial port and which tracked item is attached to the viewer or to the LCD shutter glasses These settings are provided by the Tracker section of the INI file The following section lists each key in bold text followed by a brief explanation Device This specifies the name of the tracking system that we wish to use for head tracking This is passed directly to TrackLib which searches for a match within the list of supported tracking systems If a tracking system is found by a case insensitive sub string search it attempts to connect to that system If the tracking system cannot be found an error is displayed and the tracking option is disabled Some examples are shown below which denote the Polhemus Fa
12. Y axis vector is set to the Z axis 0 0 1 and the Z axis vector is set to the Y axis 0 1 0 The position offset P in the TrackerXForm accounts for the position of the transmitter relative to screen centre In this case the transmitter origin was located 51cm right of the screen centre 38cm in front of the screen plane and 27cm below the screen centre 36 The GlassesXForm specifies the transformation between the tracking system receiver and a point that lies halfway between the two eyes of the viewer In this case the receiver was mounted on the right arm of a pair of CrystalEyes glasses facing towards the monitor with the base of the receiver mounted flush against the outside of the arm of the glasses The receiver cable was taped to the end of the arm just above the ear The viewing direction of the user was assumed to be along the X axis of the receiver but the camera in our scene looks along the Z axis Therefore the X vector in the GlassesXForm is set to point along Z axis 0 0 1 Similarly the up vector of the camera is on the Y axis whereas the up axis of our receiver is Y Therefore the Y vector in the GlassesXForm is set to the Y axis 0 1 0 Finally the Z axis of our receiver points along the X axis so the Z vector is set to the X axis 1 0 0 It s important that these three vectors form an orthogonal right handed coordinate frame There is a position offset of 7cm to account for the fact
13. convenience to the user If you want to perform more general or more complex transformations then an alternative is to use the modifier feature see SetModifier function for details SetAngleY Applies a rotation about the Y axis vertical axis given an angle in degrees The rotation angle can be positive or negative For example to rotate the scene by 45 degrees vrvis SetAngleY 45 This function is a convenience to the user If you want to perform more general or more complex transformations then an alternative is to use the modifier feature see SetModifier function for details SetBackCol This function allows the background colour of the scene to be changed The default is to use a black background The colour is specified as three values Red Green and Blue each in the range zero to one Examples vrvis SetBackCol 1 1 1 white background vrvis SetBackCol 0 5 0 0 medium red background vrvis SetBackCol 0 0 0 black background Note if you enable the underlay mode see documentation of UseUnderlay function the background colour will be ignored UseStereo This function determines whether the application should run with or without stereoscopic display for example using LCD shutter glasses Not all hardware is capable of running in stereo If stereo is not supported VRVision defaults to the normal mono display mode Examples vrvis UseStereo 1 enabl stereo if possible vrvis UseStereo
14. functions are called after VRVision has finished displaying the scene and returned control to Matlab They are used to retrieve information from VRVision such as which key was pressed to quit or the elapsed time until the user hit the key GetQuitKey This function returns the key that the user pressed to quit It will only contain a valid key if the key quit option has first been enabled with the UseQuitKeys function The key is returned as a character array string To distinguish the joystick buttons from any other key on the keyboard they are named JOYO through to JOYO Example k vrvis GetQuitKey 11 GetQuitKeyTime This function returns the time in seconds that elapsed between the first drawing that the application did onset of stimulus and the user pressing one of the accepted quit keys The resolution and accuracy are system dependent There is more information about timing accuracy on the VRVision web site If the user didn t press a key this function will return zero Example t vrvis GetQuitKeyTime 12 6 Scene Files This section briefly describes some of the effects that can be achieved by creating and editing OpenInventor or VRML scene files 6 1 Lighting In common with most real time graphics applications VRVision uses a relatively simple lighting model This is sufficient for simple lighting effects including directionality of light intensity and colour It does not inc
15. here along with some examples of suitable glasses and display monitors Many of the techniques described above will function with VRVision providing that the device in question is compatible with the OpenGL quad buffer stereo format However there are some displays certain of the new free viewing flat panels for example that will not be directly compatible Shutter Glasses There are several different varieties of LCD shutter glasses available and a comprehensive review is not possible here However two suitable models that are worth considering are the CrystalEyes StereoGraphics Corp and the nuVision 60GX MacNaughton Inc These both have reasonably large LCD panels so as not to restrict the field of view of the user are relatively comfortable to wear and have good compatibility with most workstation graphics cards that have stereo support When buying glasses it is important to check for compatibility with the graphics card in question The preferred interface is the 3 pin VESA stereo DIN connector This is simply a miniature 3 pin DIN socket which provides power to the glasses and a synchronisation signal to switch the LCD panels at the appropriate moment If you have a graphics card that does not offer the 3 pin VESA stereo connector then you will need an external interface of some kind to derive the synchronisation signal from the VGA connector For example the StereoEnabler StereoGraphics Corp and the nuVision 60GX N
16. hundreds or thousands of triangles described in the same way There is also a downloadable script ivsurf which generates surfaces of this type from within Matlab 21 T Initialisation File There are many different preferences and settings that can be altered through the VRVision initialisation file also referred to as the INI file This is simply a text file that can be edited with most text editors These settings are then loaded automatically when VRVision starts Therefore if you make changes to the INI file you will need to restart VRVision for them to take effect The file is named vrvision ini It should be placed in the working directory of the VRVision plug in If the file cannot be located an appropriate error message is output to the Matlab window The format of the file is basically the same as the standard Windows INI file format It consists of a number of different sections and each section contains one or more keys For example the settings that describe the width and height of the display screen are described in the INI file as follows Screen Width 0 4 Height 0 3 In the example above the section name is enclosed in square brackets Screen and the keys are named Width and Height This describes a display monitor with a width of 40cm and height of 30cm since the values are specified in metres Each key is associated with a different setting or preference and has a particular value which can be alter
17. scene is viewed from a static viewing position The position consists of three comma separated values specifying the X Y and Z coordinates of the viewer For stereoscopic display this defines the midpoint between the two eyes The origin is at the centre of the display surface When facing the display the X axis points right the Y axis points up and the Z axis points out of the screen towards the viewer 23 For example to place the viewer position in the dead centre of the screen at 50cm distance the following settings would be used Position 0 0 0 5 Although the initial viewer position can be specified in the file it is often overridden by setting the view position from a Matlab script or by using head tracking View This defines the viewing direction vector It is a unit length direction vector that controls the direction in which the camera is aimed Since the viewer will be facing towards the screen this is normally set to 0 0 1 to indicate that the camera is aimed along the Z axis It should not be necessary to alter this setting For example View 0 0 1 Up This defines the up direction vector It is a unit length direction vector that defines the up axis of the camera Since the Y axis of the screen points up from the point of view of a user the up axis of the camera is also set to lie on the Y axis Therefore this key is normally set to 0 1 0 It should not be necessary to alter this setting For example
18. specify that item 1 is used to track the glasses by adding this line to the Tracker section of the INI file GlassPort 1 7 4 TrackerXForm When the tracking system reports the position of a tracked object to VRVision it will almost certainly use a different coordinate system to that of the display For example the tracking system origin for the Polhemus Fastrak will be located at the centre of the magnetic transmitter not the centre of our display surface Furthermore the X Y and Z axes will not usually be aligned with those of the display For this reason VRVision allows you to specify a transformation matrix which defines how to transform from the tracking system coordinate frame to that of the display This is specified in terms of the unit length direction vectors of the X Y and Z axes and a position vector P that defines the translation component For example the settings below were used for a Vicon tracking system where the tracking system X axis was aimed towards the screen the Y axis pointed left and the Z axis pointed up The coordinate axes in VRVision are completely different with the X axis pointing right the Y axis up and the Z axis pointing out of the screen The tracking system origin was also located 1 2m vertically below screen centre at 3m distance The transformation matrix given below allows VRVision to transform between these two very different coordinate spaces TrackerXForm X 0 0 1 ViconX Scr
19. that the receiver is placed some distance to the right of the eye centre 37
20. vrvis You should see that the scene is displayed in wireframe The proper use of modifiers can simplify the process of setting up several different experimental conditions without modifying the scene file itself For example in a face recognition study the scene files would contain the VRML face models and the modifiers might specify different lighting conditions Some understanding of OpenInventor or VRML nodes is needed to be able to make the best use of this feature SetViewPos Sets the default viewer position X Y Z coordinates in metres This will be used in preference to the value given in the INI file under the Camera Position key the INI file settings are explained in more detail in section 7 If head tracking is enabled the viewer position is controlled by the tracking system instead This setting will typically be used when the viewer is always in a fixed viewing position for example when seated in front of the screen or if a chin rest is used to position the head If you call SetViewPos without arguments it restores the default setting from the INI file The origin 0 0 0 is the centre of the screen From the point of view of the user the X axis points right the Y axis up and the Z axis points out of the screen For example to place the viewer 2m distant from screen vrvis SetViewPos 0 0 2 To restore the INI default setting call the function without any parameters vrvis SetViewPos SetScenePos
21. 6p5 work 3 Restart Matlab to make sure that the vrvision module is loaded VRVision itself is a standard Matlab MEX file which consists of a Windows DLL This DLL must be in the Matlab MEX search path so that it is found when vrvis is typed at the Matlab prompt The ZIP file includes a number of other DLL files that are needed by VRVision as well as an initialisation INI file and a sample scene It is important that all the files are installed otherwise VRVision will not load The INI settings file must be placed in the same working directory as the VRVision DLL However the remaining files can be placed anywhere in the Windows search path For example you can place them in the Windows system directory or create a new folder and add it to the Windows search path After changing file locations and search path settings it might be necessary to restart Matlab for the changes to take effect 4 Getting Started For those who dislike reading lengthy instructions here is a very brief introduction to get you started il 2 Install VRVision as described in Section 3 Obtain an OpenInventor or VRML 1 0 model file extension iv or wrl There are some sample files provided on the web site http www hive hull ac uk software vrvision Note that VRML97 VRML 2 0 are not currently supported by SGI OpenInventor Your scene may be too big or too small to display by default or it may be positioned far away from the origi
22. SR emitter MacNaughton Inc both connect to the VGA port of a graphics card You will need to check that your graphics card and drivers are compatible with these devices before buying 30 Technical information on the glasses and compatibility issues is available from the following sources http www stereographics com CrystalEyes glasses http www nuvision3d com nuVision glasses http www stereo3d net reviews information http www stereovision net forum links news Monitors The shutter glasses function by alternately blocking the left and right eye using liquid crystal shutter panels in synchronisation with the display The left and right eye images are displayed alternately so that each eye will receive a different image resulting in a stereo effect For this to work the image must persist on the display for a very short time which in practice means that only CRT monitors are suitable Unfortunately LCD flat panel monitor and plasma displays are currently too slow to be compatible with shutter glasses If the image persists for too long there will be no stereo effect or at least a very severe ghost image this term means that the left eye image can be partially seen on the right eye and vice versa Therefore you should select a good quality CRT monitor preferably one with a short persistence phosphor The second problem is that the vertical refresh frequency of the monitor is effecti
23. StereoGraphics Corp and nuVision 60GX MacNaughton Inc However they are relatively expensive workstation class graphics cards For detailed specifications and reseller information please visit the manufacturer web site http www 3dlabs com In order to use stereo support on these cards you must select a Frame Sequential Stereo display mode using the Display Settings dialog The nVidia Quadro GeForce family The nVidia Quadro family is targeted at professional workstation market and offers excellent OpenGL performance and stereo support at a competitive price The nVidia GeForce is based on the same chip set but targeted at the consumer market and lacks some of the features of the professional card such as quad buffer stereo support In both cases driver support is excellent with a good OpenGL implementation The Quadro cards are available with 3 pin VESA stereo connectors making them compatible with most stereo shutter glasses including CrystalEyes StereoGraphics Corp and nuVision 60GX macNaughton Inc For cards that do not feature the 3 pin VESA stereo connector it is still possible to connect stereo shutter glasses by using an external interface box such as the StereoEnabler StereoGraphics Corp which attaches to the VGA connector of the graphics card and converts this to a 3 pin VESA output This is only possible if the graphics driver is able to place the appropriate stereo synchronisation signal on the VGA p
24. VRVision User Manual Version 1 07 James Ward University of Hull UK 20 May 2003 Last updated 1st August 2004 All trademarks acknowledged TABLE OF CONTENTS Mwst 1 EN nunc 2 2 1 Software Requirements sses ORO NORD EAE A E 2 2 2 Hardware Requirements eere HIE E OA SERA EE YEERUR SES UNE Fe EREER ERE T SEP E BEY A 2 Se Installation icis ODDO ENIM 3 dE Ee Le E DEER 4 9 Function Reference soie nth Dee DOCTI n SIDE LIE 5 Stee DD eg 5 SEELEN 5 SE EE 5 Set Vie wPOs usos E ii on ODORE tie 6 SEENEN H EE EE Ee H e H e EE H e EE 7 LOES P 8 UseH ad Track C 8 UseTime LINE is be 8 round m 8 rdi c C E 9 HEU T E X 9 LR RE c 9 Use FUS CHEM T 10 OR LOEn E E T X HH HO 10 Record TORU eseon PUE 11 Ertrag EE e a E OE E E r EE EEEE RAE PAEO TEER ERGS 11 MUTI POS neer te DR EE IUNGERE IARE P oencetasdeyaosassanieaacteguuseseeeeviaases 11 29 2 Query FUNCH ODS 352055235505 reee ronca Ev EE PEPPER PNE EERSTEN DER EE PURUS ieis 11 EEN est HUE E 11 EE RT Re EEUU 12 EEN UE 13
25. and gt gt vrvis This will start the main VRVision application and display the current 3D scene However before doing this you would normally need to set up some parameters for example to specify which scene file to load There are a number of functions provided for this purpose Every function consists of a call to VRVision with the name of the function passed as a text string followed by an optional list of parameters For example to call the SetFilename function gt gt vrvis SetFilename myscene iv Functions fall into two main categories 1 Setup functions that set parameters before running VRVision 2 Query functions that retrieve data or results after VRVision has finished running 5 1 Setup Functions These functions can be called before the application runs to configure various settings such as which scene file to load or the viewer position Most of these settings will persist between successive runs of VRVision unless stated otherwise Many of them are also configurable from within the INI file in which case the INI file setting acts as a default that is overridden when you change the setting from within Matlab SetFilename Specifies which 3D scene file should be loaded when VRVision runs If no file is specified the filename given in the INI file will be used instead The current version directly supports files with the following formats VRML 1 0 OpenInventor 2 1 ASCII or binary Examples
26. aphics industry moves very quickly it is likely that the cards described here will soon be replaced by a new generation The general requirements are as follows 1 Must support hardware accelerated OpenGL 1 2 or above 2 Must support quad buffer OpenGL stereo that is to say it must be possible to create an OpenGL window with a stereo pixel format In general these tend to be classed as workstation graphics cards 3 The graphics card must be compatible with your choice of stereoscopic display hardware For example if your LCD shutter glasses have a 3 pin VESA stereo 31 connector then you must use a graphics card that features this connector or you must use an external adaptor When selecting a graphics card be aware that many consumer class graphics cards support a specific type of stereo 3D that is designed for use in games This does not necessarily mean that these cards support true quad buffer stereo in OpenGL which is required for VRVision At time of writing there is an excellent summary of compatible 3D hardware available on the StereoGraphics web site http www stereographics com support boards brd chrt htm The 3DLabs Wildcat family The 3Dlabs Wildcat 3 6110 6210 and Wildcat 4 7110 7210 are workstation class graphics cards that offer accelerated OpenGL support and feature a 3 pin VESA stereo connector These cards are directly compatible with most stereo shutter glasses such as CrystalEyes
27. d This option can be used to turn the head up display on and off which displays statistics about the rendering performance Currently this is limited to a simple display of the frame rate indicating the number of frames per second that can be achieved for a particular scene You will normally want to leave this option disabled but it can be useful to know the current frame rate when setting up an experiment or to see what effect a particular feature such as stereo or anti aliasing has on performance ShowHud 0 hide head up display ShowHud 1 show head up display IVCacheMin This is used with a customised version of the OpenInventor graphics library to set the IV AUTO CACHE MIN environment variable This affects the caching policy of OpenInventor and can improve performance in some cases by allowing it to cache complex scenes by constructing an internal display list for more efficient rendering For example IVCacheMin 1000 alter OpenInventor cache limit CaptureMouse This option determines whether VRVision uses mouse capture within Windows to capture mouse messages CaptureMouse 0 don t capture mouse default CaptureMouse 1 capture mouse input 28 7 7 Joystick This section contains settings that affect the behaviour of the joystick or game controller These settings influence the sensitivity of the joystick when it is used to manipulate objects The following section lists each key in bold text followed b
28. d VRVision will still raise itself above other windows but in a less forceful way which is the default ForceTopMost 0 vaise window to top politely ForceTopMost 1 force window on top ForceStereoPF When using stereoscopic display in OpenGL VRVision automatically creates a window with a stereo pixel format If the ForceStereoPF option is enabled this will cause VRVision to always use a stereo pixel format regardless of whether the stereoscopic display is enabled For example in an experiment this will ensure that the LCD shutter glasses are enabled i e flickering even when displaying monoscopic images This means that an experimental participant can wear the glasses in both monoscopic and stereoscopic conditions and will therefore experience similar flicker and display brightness in both cases ForceStereoPF 0 use stereo only in stereoscopic mode ForceStereoPF 1 always use stereo even for monoscopic Note that there is a performance cost associated with the use of a stereoscopic pixel format since it is necessary to render the scene twice once for the left eye and once for the right eye Therefore this option is only recommended for special cases such as the example described above ShowCursor This option determines whether the mouse cursor is visible when VRVision runs in fullscreen mode The mouse cursor is hidden by default ShowCursor 0 hide mouse cursor default ShowCursor 1 Show the mouse cursor ShowHu
29. dard game controller within Windows should be compatible with this option This function supports the same rotation angle limits as the UseJoyMove function including the ability to lock an axis by specifying an angle limit of zero When using the joystick for movement you can also use the joystick buttons Please see the UseJoyQuitKeys function for details Examples vrvis UseJoyMove 1 enable joystick movement vrvis UseJoyMove 0 disable joystick movement vrvis UseJoyMove 1 45 0 allow 45 rotation about X vrvis UseJoyMove 1 0 45 allow 45 rotation about Y vrvis UseJoyMove 1 15 15 allow 15 rotation about X Y Joystick rotation can be recorded to file and replayed later Please see the RecordToFile and PlayFromFile functions for further details UseJoyQuitKeys This function allows you to specify which joystick buttons keys can be used to quit from the application When the application quits it will return to Matlab The default is to disable quit keys You can specify a character string listing the acceptable button numbers or you can specify the special string any which will accept any button press on the joystick Button numbers range from 0 to 9 inclusive with O being the first joystick button The numbering of buttons will vary from one joystick to another Some joysticks provide a utility for reassigning buttons at driver level Examples vrvis UseJoyQuitKeys 01 quit if bu
30. e Scene Graph Internally VRVision builds an Open Inventor scene graph that describes the scene to be displayed and determines the order in which various transformations such as rotation scaling and translation are applied to the scene This section illustrates the typical structure of this scene graph and how it is affected by various options given to VRVision Default Scene Graph The figure below shows the scene graph in the default state without any options specified in the INI file Note that the X and Y rotation nodes are immediately before the Scene This means that any rotation for example using the SetAngleY function will take place about the origin of the scene itself i e as it appears in the Inventor or VRML scene file Root Separator Camera Light Translation Scale Translation X Rotation Y Rotation Scene scene pos auto centre You can select this behaviour by specifying the following options in the INI file before starting VRVision Scene RotateFirst 0 this is the default This is the default behaviour if the RotateFirst option is not specified in the file it is assumed to be zero disabled 17 Rotate First Option There is an option in the INI file that can be used to force the X and Y rotation nodes to be inserted before the Translation auto centre This means that if both the auto centre and the rotate first options are enabled in the INI file the scene will be automatically repositioned at th
31. e below R G B Colour 0 0 0 Black 1 0 0 Red 0 1 0 Green 0 0 1 Blue 1 1 O Yellow 0 1 1 Cyan 1 0 1 Magenta 1 1 1 White The light can be turned on and off by setting the on property to TRUE or FALSE respectively This feature is probably not very useful for this application Material Properties The material properties of objects within the scene must be carefully considered to achieve the desired appearance For example it is possible to achieve gloss or matte surface qualities to control object self illumination glow emissive lighting and rudimentary transparency effects In some cases the material properties might already be contained within the scene file particularly when it has been exported from a 3D modelling package It is possible to specify custom material properties by adding the following text to a scene file or modifier However bear in mind that your settings might later be overridden by settings within the scene file itself 15 Material ambientColor diffuseColor specularColor emissiveColor shininess 0 transparency 1 The ambientColor value is a simple colour value that simply adds to the apparent brightness of the object and does not consider the lights within the scene It is specified as three values in the range 0 to 1 representing the Red Green and Blue components of the colour The diffuseColor determine
32. e light is aimed in see Directional Light above The cutOffAngle is the angle in radians measured from the direction vector where the cone of light will be cut off This can be considered as the angle of the lampshade in the diagram above In the example above the angle is set to the default value of 45 PI A 0 785 14 The dropOffRate is the rate at which the light intensity drops off decreases as the angle between the ray of light and the direction vector increases The value must be between 0 where the cone of light has equal intensity throughout and 1 which specifies a narrow beam of light Common Light Properties There are some common properties that apply to all of the light types described above These allow the intensity and colour of the light to be adjusted and allow a particular light to be turned off and on The following example illustrates the default settings for the three common properties on a directional light source They are equally applicable to point and spot lights DirectionalLight on TRUE intensity 1 color 1 1 1 The intensity value allows the brightness of the light source to be adjusted The valid range is from 0 no light to 1 maximum brightness The color value specifies the colour of the light source in terms of three separate components red green and blue Each component ranges from 0 minimum to 1 maximum Some typical colours are listed in the tabl
33. e necessary to rename the file after saving When you have saved the file you can try loading it into VRVision from the Matlab prompt as shown below gt gt vrvis SetFilename cube iv gt gt vrvis To ensure that the cube is visible it is suggested that the automatic scaling feature is enabled in the initialisation file Otherwise the SetScale command can be used from within Matlab to adjust the scale In the example above the first line is a special header that indicates that this is an Inventor file including a version number and that it uses the ASCII plain text format All the examples shown here will include this header The remainder of the file describes the scene graph In this case the scene graph consists of just a single node which is a cube You will notice that after the name of the node Cube there is an open and closed curly bracket and H Every node has a number of fields which are usually parameters such as width height depth or radius You can set these fields to a particular value by listing the field names and values between the curly brackets For example the cube node has width height and depth fields You can set them as shown below Inventor V2 1 ascii Cube width 1 height 0 5 depth 0 25 Try modifying the file with a text editor so that you can see the effect of these fields Note that if you don t set a particular field value the default values will be used
34. e origin based on the scene bounding box and then rotated The resulting scene graph is shown below Root Separator Camera Light Translation X Rotation Y Rotation Scale Translation Scene scene pos auto centre These options are very useful if the VRML or Inventor scene file has an origin that does not lie near the centre of the object You can select this behaviour by specifying the following options in the INI file before starting VRVision Scene AutoCentre 1 enable automatic centre option RotateFirst 1 rotate before translate Note that this is only a small extract from the INI file There are many more options detailed in section 7 6 3 The Open Inventor File Format This section contains some background information about the Open Inventor file format as used by VRVision This is too large a topic to cover in detail here but after reading these few examples it should be possible to construct and edit some simple scenes and to have a basic understanding of the structure and capabilities of Open Inventor files The Open Inventor 2 1 file format Silicon Graphics Inc supports a plain text ASCII format as well as a binary format which is more compact and loads faster This section will concentrate on the plain text format which makes it relatively easy to edit and create Open Inventor files manually It is also possible to create them automatically from within a Matlab script and an example of such a script ivsurf m
35. e strips Each triangle strip consists of one or more triangles connected in a continuous strip and defined by a number of vertices corner points Within a strip each triangle shares one edge and two vertices with its immediate neighbour The vertices points and triangle strips are listed separately in the file We start by listing the X Y Z coordinates of each point and then declare the triangle strip set Within the triangle strip set we list the index number of each vertex This is much easier to demonstrate with an example Inventor V2 1 ascii Separator Coordinate3 point 000 100 ql d IndexedTriangleStripSet coordIndex Oy ly 27 I In the example shown above the file begins with the Coordinate3 node whose point field lists the X Y Z coordinates of each triangle vertex In this case the vertices are located at 0 0 0 at 1 0 0 and at 1 1 0 The next node in the file is an IndexedTriangleStripSet which defines a single triangle in this case Within this node the coordIndex field defines one triangle strip consisting of vertices 0 1 and 2 The end of the triangle strip is marked by the special value 1 Note that the vertices are specified by a number which indicates their position within the vertex list starting from zero This is more efficient because a single vertex can be used within a number of different triangle strips You will find more examples on the VRVision web site which include
36. ed by the user The names of the sections and keys are predefined and cannot be altered However the values can be changed and it is not necessary to include all the supported keys If a particular key is missing the default setting will be used for that key If a section or key appears more than once the last value to appear in the file will be used We do not recommend that you do this because it is redundant and because it will be confusing for anyone reading the INI file later It is also possible to include comments in the INI file which are useful to explain the meaning of a particular key and to document why a particular value is used for a given key Comments are denoted by using the semi colon character at the start For example we might document the screen settings with the make and model of the monitor so that a user will know which monitor the INI file relates to Screen Iiyama Vision Master Pro 452 This is the width and height of the display in metres Width 0 365 Height 0 275 The remainder of this section lists the supported sections and keys explains which values are acceptable for each key and what effect this has on the behaviour of VRVision 7 1 Screen The Screen section contains settings that describe the physical size of the display screen This should be the width and height of the visible image on the display surface in metres rather than the outer dimensions of the monitor The monitor should fi
37. eenZ Y 1 0 0 ViconY ScreenX Z 0 1 0 ViconZ Screeny P 0 1 2 3 1 2m on Y axis 3m on Z axis If the tracking system axes happen to match those of VRVision and only a simple position offset is required the X Y and Z vectors would be specified as shown below 25 X 1 0 0 Y 0 1 0 Z 0 0 1 Then the P value can be used to specify the X Y and Z position offset 7 5 GlassesXForm If a tracking receiver or target is attached to a pair of LCD shutter glasses or perhaps to a headband it can be used to track the position of the viewer However the tracking system will report the position and orientation of the object being tracked whereas VRVision requires the position and orientation of a synthetic camera located at the midpoint between the eyes of the viewer The GlassesXForm section allows you to specify the transformation from the tracked object to the midpoint between the eyes As with the TrackerXForm the transformation matrix is specified in terms of three unit length direction vectors of the X Y and Z axes and a position vector P For example when the Vicon system reports the location of the glasses the X axis is aligned with the viewing direction the Y axis points left and the Z axis points up However our synthetic camera is arranged so that the viewing direction is along the Z axis towards the screen the up vector is the Y axis and the X vector points to the right For this example the origin of
38. en disabled the fixed viewing position is used this is read from the INI file by default and can be overridden by the SetViewPos function from Matlab When using a tracking system most of the configuration settings are read from the INI file since they are not usually changed during the course of an experiment These settings include information about which communication port the tracker is connected to and calibration settings that account for the placement of the tracker relative to the screen and the glasses 9 1 Supported Tracking Systems At present the following tracking systems are supported 1 Ascension Flock of Birds electromagnetic 2 Vicon Real Time Server 3 Polhemus Fastrak electromagnetic 4 Logitech 3DMouse ultrasonic We have access to all the systems listed above and are prepared to support them If problems are reported with any of the systems above and can be reproduced locally then we will try and provide a solution This is done as a courtesy and does not constitute a guarantee The following systems are partially supported or unsupported That is to say they have either not been extensively tested with VRVision or they are still under development In some cases we do not have access to the system so continued development and testing is not possible 1 Image Guided Technologies Flashpoint 5000 optical 2 Northern Digital Polaris 3 Qualisys Track Manager Real Time 4 Intersense various
39. erlay is enabled the screen is captured just before VRVision appears Therefore you should do your drawing just before running VRVision The underlay feature only really makes sense when VRVision is running in fullscreen mode otherwise the screen contents will be displayed in a much smaller window VRVision uses one of two methods to display the underlay 1 Texture map method 2 Blitter method The quality and speed of the two methods will vary between different graphics card and driver combinations In fact the texture map method may not work at all if your graphics card cannot create texture maps at full screen resolution Therefore you should pick the method which works best on your card You can do this by modifying the INI file as described below Under the Scene section of the INI file use either of the following keys UnderBlit 0 use texture map method OpenGL texturing UnderBlit 1 use blitter method OpenGL glDrawPixels If this option is missing from the INI file the default is to use the texture map method 10 RecordToFile This option causes the camera movement and or mouse movement to be recorded to file so that it can later be analysed or replayed It is typically used in conjunction with head tracking For example the data could later be used to examine the motion of the users head during a particular task The function takes a single parameter the filename to record to If the file already exists i
40. he object or the centre of the bounding box Also refer to the RotateFirst option RotateFirst This option forces the X and Y rotation nodes to be inserted before the Translation node that is used to implement the auto centre feature This means that if both the AutoCentre and RotateFirst options are enabled the scene will be automatically repositioned at the origin and then rotated This is explained in more detail in section 6 2 For example RotateFirst 0 rotate after translation RotateFirst 1 rotate before translation UnderlayBlit VRVision is able to automatically capture the contents of the screen before it starts see the UseUnderlay function for more information and to display this as a textured background behind the objects that it renders VRVision implements two different methods to achieve this since the performance and quality of each may vary from one graphics card to another This INI file option selects which implementation is used UnderlayBlit 0 Use texture mapping method UnderlayBlit 1 Use blit block transfer method If a particular method does not perform well on your chosen graphics card you can try changing this option to see if it improves the speed or quality 27 ForceTopMost If enabled this option causes VRVision to force itself on top of all other windows on the desktop On the Windows operating system it does this by applying the top most window property If this option is disable
41. hould see your Graphics Processor identified as a Quadro if not then you are unlikely to have stereo support Plug and Play Monitor and N IDIA Quadro2 MXR EX Properties 2 X General Adapter Monitor Troubleshooting Color Management E Quado2MXR EX A aen Display Adapter Information Graphics Processor Quadro2 MXR EX Bus Type AGP A BIOS Version 3 11 00 18 33 NVIDIA On Board Memory 32 MB e IRQ n WC System Information System Processor Intel Pentium r III with SSE Total Physical Memory 261 620 KB Free Physical Memory 73184 KB Driver Version Information Filename D Version nv4 disp dl Display driver 5 13 10 3140 nv minisys Display driver miniport 5 13 10 3140 nvogint dil OpenGL installable client driver 6 13 10 3140 nvcpl dll Display Properties extension 5 13 10 3140 nvqtwk dll Taskbar utility library 5 13 10 3140 zi NVIDIA on the Intemet gt gt Figure 2 Advanced Properties Dialog Click on the Additional Properties button to proceed and you should then see the additional properties dialog Figure 3 You will need to click on the tab for OpenGL settings to see the options shown below 33 Additional Quadro2 MXR EX Properties EET Use unified back depth buffer V Enable quadbuffered stereo API D Enable Overlays Use desktop colour depth Auto select Off by default Disabled Figure 3 Additional OpenGL Pr
42. i Cube Translation Translation 2 0 0 Scale scaleFactor 0 5 0 5 0 5 Cube Note that the Scale node takes a vector of three values These specify the scale factor on the X Y and Z axes respectively Similarly the Translation node takes a vector which specifies how far to move the object on each of the X Y and Z axes Example 3 Using Separators There is a special node called the Separator which allows nodes to be grouped together in such away that any transformations materials or other attributes are only applied to that group and will not affect other nodes in the scene graph An example of this is shown below Inventor V2 1 ascii Separator RotationXYZ axis Y angle 0 785 Cube Cube In the example above we create a Separator node which contains a RotationX YZ node and a Cube node The rotation will be applied only to the first cube in the scene The second cube is not affected since it lies outside the separator 20 Example 4 Complex Surfaces Here we provide a brief example of how more complex surfaces are represented within the Inventor file You would not normally edit the structures described here by hand but this information may be of use if you intend to write a script or program to generate such surfaces automatically Complex surfaces are described with a mesh of interconnected triangles which define the surface of the object Usually these take the form of a set of triangl
43. ill make the stick more responsive Some joysticks may offer similar parameters within the control panel and device settings For example Scale 0 1 29 8 Hardware for Stereoscopy This section outlines some of the hardware requirements if you wish to use the stereoscopic feature within VRVision Stereo support has improved considerably on graphics cards but can still be problematic in some cases However with the right choice of equipment it is possible to achieve a good quality stereoscopic display on relatively inexpensive PC based commodity hardware 8 1 Display Devices There are many possible methods for displaying stereoscopic imagery some of which are listed here briefly 1 CRT monitor with LCD shutter glasses Stereo capable CRT video projector with LCD shutter glasses Stereo capable DLP video projector with LCD shutter glasses CRT LCD DLP with Z Screen polarizer and polarised glasses 2 3 4 Pairof LCD DLP projectors with polarising windows and polarised glasses 5 6 CRT LCD Plasma monitor with surface mounted lens array 7 CRT LCD Plasma monitor with grating Barrier stereo method This list is by no means comprehensive and the range of commercially available stereo display systems continues to expand However arguably the most commonly used display system for stereoscopy on the desktop is the combination of LCD shutter glasses and a CRT monitor This is the solution that we will describe
44. instead Example 2 Transformations It is possible to move rotate or scale objects within the scene graph This is achieved by inserting one or more transformation nodes Some examples of transformation nodes are listed below RotationXYZ rotate a node about the X Y or Z axis Scale change the scale of a node Translation move an object change the position You can apply multiple transformations to an node for example to change both the scale and position of an object The transformations will be listed in the Inventor file in the order that you wish to apply them The node or object that you wish to transform should appear after the transformation node s 19 For example we can modify the cube iv file seen in example 1 so that the cube is rotated by 45 degrees about the Y axis This involves adding a RotationXYZ node immediately before the Cube node However the rotation angle is specified in radians rather than degrees so we must first convert our rotation angle into radians 45 x PI 180 0 785 The rotation node is then added to the file as follows Inventor V2 1 ascii RotationXYZ axis Y angle 0 785 Cube Note how the rotation axis and angle are specified in the rotation node and that the cube node appears after the rotation node The scale and translation node are used in a similar way The example below shows two objects one of which has a combined scale and translation applied Inventor V2 1 asci
45. ish to display complex 3D scenes thousands of polygons texture maps etc then a reasonable minimum specification is Pentium III 1GHz CPU 256Mb RAM nVidia GeForce 2 MX graphics card note does not support stereoscopic display If you wish to use the stereoscopic display feature then you will also need a graphics card that supports quad buffer OpenGL stereo and an appropriate display device For more details please refer to Section 7 which covers the topic in more detail Similarly if you wish to use the head tracking feature then you will need access to one of the tracking systems that are supported by VRVision which are listed in Section 9 3 Installation The VRVision software can be downloaded from the web site as single ZIP file which contains all the files needed to get you started You can download the software from the following address http www hive hull ac uk software vrvision Having downloaded the software you can unzip all the files into the Matlab work folder and restart Matlab If you don t want to place these files in your work folder you can create a new folder and alter the Matlab search path accordingly The following is a step by step installation example 1 Download the complete VR Vision software as a ZIP file 2 Unzip the files into the Matlab working directory You can install them in another directory if you wish but make sure that it is in the Matlab search path For example c matlab
46. lude effects such as shadows at present VRVision supports three different types of light source e Directional Light e Point Light e Spot Light As a special case it is also possible to disable lighting so that the object colour and photo texture are used directly For example if a texture map already includes natural lighting and shadows this can be displayed directly without use of an additional synthetic light source Directional Light The directional light source is considered to be at an infinite distance from the subject so that the rays of light can all be treated as being parallel Therefore the light source is specified only as a direction vector The closest real world analogy would be the sun illuminating an object on the earth Light The light source is defined in the Inventor iv file as follows DirectionalLight direction 0 0 1 The direction of the light source is specified by a vector consisting of three values These represent the X Y and Z components of the vector In the example above the direction is set to the negative Z axis which causes the light to point into the screen This will cause the scene to be evenly lit from the front The three components of the direction vector allow the light to be aimed in any direction you wish Preferably the direction vector should have unit length That is to say the sum of the squares of the three components should add up to one
47. material In this case it can be desirable to use the texture map colour values directly and to disable external light sources This can be achieved by inserting the following into the scene file LightModel model BASE COLOR When specifying this lighting model there is no need to specify any additional light sources or to enable the headlight in the INI file since the texture map colour will be used directly Instead of modifying the original scene file it would be better practice to create a separate modifier file containing the light model settings An example of a typical modifier file called unlit iv is shown below 16 Inventor V2 1 ascii LightModel model BASE COLOR From within Matlab you can then specify the original scene file and the modifier as follows vrvis SetFilename YourScene iv vrvis SetModifier mod unlit iv When the VRVision viewer is next started the chosen modifier will be applied before loading the scene file so that lighting will be disabled This technique makes it possible to apply any number of different lighting conditions to the original scene file Animated Light Sources It is possible to animate light sources by using the OpenInventor engines such as the ElapsedTime and Calculator nodes For example 1 Vary light intensity as a function of time 2 Turn lights on and off in sequence 3 Move lights along a predefined path 6 2 Th
48. n Also if your scene doesn t contain lights you should turn on the headlight For these reasons when running VRVision for the first time you might want to use a text editor e g notepad to edit some of the settings in the vrvision ini file to match the ones shown here Scene Headlight 1 turn on the headlight Scale auto use automatic scaling AutoCentre 1 automatically move scene to origin Start Matlab normally Instruct VRVision to load the scene and display it gt gt vrvis SetFilename yourscene iv gt gt vrvis If that was successful you will find the other supported functions documented in Section 5 The best way to understand what is possible and how to use the supported functions is to work through the different commands in the function reference at a Matlab command prompt In this way you can immediately see the effect of the different options on the behaviour of VRVision 5 Function Reference This section lists the functions supported by VRVision explains their parameters and provides some examples of how they can be used in practice All the examples shown here are typed at the Matlab prompt or called from within a Matlab program M file There are two ways that VRVision can be called The first one is to call the main function without any parameters You can either use the full name of the function vrvision as shown here gt gt vrvision Alternatively you can use the shorth
49. operties At this point you should make sure that quadbuffered stereo API is enabled and overlays are disabled Your settings should match those shown in the upper white box in Figure 3 Having made these changes you should be able to run VRVision in stereo Note that it may be necessary to restart Matlab and VRVision before the changes take effect While you are in the Display Properties dialog you should change the vertical refresh frequency to the maximum that your monitor can safely support for the current display mode This is changed using the Monitor tab as shown in Figure 4 Please check which modes are supported by your monitor before changing this setting and test the display mode before applying changes Plug and Play Monitor and N IDIA Quadro2 MXR EX Properties lid ES Figure 4 Monitor Vertical Refresh Frequency 34 9 Tracking Systems VRVision supports head tracking if a suitable tracking system is available and has been properly configured This feature can be enabled and disabled as required by the UseHeadTrack function When head tracking is enabled the tracking system is used to measure the position of the shutter glasses and the approximate position of the left and right eyes is calculated from this The display is dynamically updated to provide an appropriate projection based on the head position of the viewer This feature is available in both monoscopic and stereoscopic display modes Wh
50. ort for example the blue line code that is used by StereoGraphics products There is more information available on the StereoGraphics web site http www stereographics com When installing the card you have the choice of either installing the drivers that came with the card or downloading the latest drivers from the manufacturer In our experience the best option is to download the latest nVidia Detonator drivers from the nVidia web site http www nvidia com Having installed the drivers you will find that quad buffer stereo is disabled by default In order to use stereo you must enable the option in the display settings dialog There follows an example of how to configure an nVidia Quadro card to enable stereo under Windows 2000 First open the display properties dialog Figure 1 either by right clicking on the desktop and selecting Properties or by opening the control panel and double clicking on Display 32 Display Properties 2 xl Background Screen Saver Appearance Web l Effects Settings Display Plug and Play Monitor on NVIDIA Quadro2 MXR EX lt Figure 1 Display Properties Dialog In the display properties dialog Figure 1 click on the Advanced button to open the advanced properties dialog Figure 2 You should click on the tab that lists the name of your graphics card which in this example is a Quadro2 MXR EX Under Display Adapter Information see Figure 2 you s
51. rst be set to the chosen display mode and refresh frequency since this can affect the image size and proportions on screen Any adjustments to the monitor settings such as width height position should then be finalised When a satisfactory image is 22 obtained the image size can then be measured using a ruler Please note also that the ratio of the width and height specified here will determine the aspect ratio used for rendering The width and height are then specified in metre units using the Width and Height keys Screen Width 0 365 Height 0 275 In the example above the displayed image is 365mm high and 275mm wide 7 2 Camera The camera settings control the position of a synthetic perspective camera which represents the viewer This is the camera that will be used when a static view position is used When head tracking is enabled some of the camera parameters are modified automatically to account for the head position of the viewer The following section lists each key in bold text followed by a brief explanation EyeSeparation This specifies the distance between the eyes in metres This setting is also termed IPD or inter pupillary distance It is only used for stereoscopic 3D rendering and has no effect on monoscopic perspective display When stereoscopic rendering is enabled two separate views are rendered by displacing the view position laterally from the camera centre position by half the eye separation to the lef
52. s the diffuse surface colour of the object when lit It is specified as three values in the range 0 to 1 representing the Red Green and Blue components of the colour The specularColor determines the specular colour when lit It is specified as three values in the range 0 to 1 representing the Red Green and Blue components of the colour The emissiveColor determines the colour of the light emitted by the object It can be used to cause an object to appear to be self illuminated without external lighting It is specified as three values in the range 0 to 1 representing the Red Green and Blue components of the colour The shininess value controls the appearance of specular highlights on the object It ranges from 0 which gives a dull matte appearance to 1 which produces glossy looking surfaces The transparency value ranges from 0 completely opaque to 1 completely transparent When completely transparent the object will be invisible Intermediate values will make the object semi transparent Multiple Light Sources It is possible to specify multiple light sources within a scene file and these can be of different types The number of supported lights and the resultant performance will vary significantly from one machine to another depending on the graphics card Base Colour Lighting It is possible to apply a texture map to the scene that includes lighting and or shadows perhaps from digital photographs or pre rendered
53. strak the Logitech 3D Mouse and the Vicon Real time system respectively Device fastrak Device 3dmouse Device vicon 24 Port This defines which port should be used to connect to the tracking system It is a string of text prefixed with port to denote a local connection or net to denote a network connection and followed by the specific port number or network address For example a tracking system connected to a local serial port such as COM2 would have the following INI file setting Port port 2 For a system such as the Vicon Real Time server this would be the network address of server For example if the server was running on a machine named nemesis the following port would be specified Port net nemesis Finally if you know that the device is connected locally but aren t sure of the port number or if the device is frequently moved around you can ask TrackLib to attempt to detect it automatically Port auto GlassPort Most tracking systems are able to track more than one item at any one time For example the Polhemus Fastrak can have four separate receivers each of which can be used to track one object It is therefore necessary to specify which of the available items is used to track the head position of the viewer for head tracking For example if we have a pair of LCD shutter glasses fitted with a Fastrak receiver and that receiver is plugged into connector 1 on the front panel of the Fastrak we would
54. t will be overwritten If the PlayFromFile option is also specified then it will take precedence over recording This function applies only to the next run of VRVision after which recording is cancelled Therefore if you want to record every time you must specify this option prior to each run which would be necessary in any case to avoid overwriting the last file Examples vrvis RecordToFile filename PlayFromFile This option is used to play back camera or mouse motion that has previously been recorded to file using the RecordToFile function The function takes a single parameter the filename to play back This function applies only to the next run of VRVision after which playback is cancelled If head tracking was enabled as well the file playback will take precedence Optionally you can specify out to make the application close at the end of playback Examples vrvis PlayFromFile filename vrvis PlayFromFile filename quit DumpPos This option forces the position and orientation data received from the head tracker to be dumped to the text console within Matlab This function is only really useful for a developer it is useful for debugging or calibrating the tracking system For example to calculate the TrackerXForm or GlassesXForm parameters for the INI configuration file Examples vrvis DumpPos 1 enable vrvis DumpPos 0 disable default setting 5 2 Query Functions These
55. t and right of centre For example we can specify an eye separation of 65mm as follows EyeSeparation 0 065 NearDist This is the distance to the near clipping plane It defines the position of the front face of the viewing frustum nearest to the viewer Any objects placed between the viewer and this plane will not be visible since they will be clipped The near and far clipping planes will affect the accuracy of the depth buffer a mechanism in OpenGL which is used to determine whether each pixel rendered is visible or occluded by another surface in the scene The depth buffer has a fixed resolution which depends upon the graphics card and drivers This resolution is divided over the entire viewing frustum between the near and far clip planes Therefore choosing clipping planes that tightly bound the scene will improve the depth buffer accuracy See also the FarDist key which is used to set the distance to the far clipping plane An example to set up both clipping planes NearDist 0 1 FarDist 100 0 FarDist This is the distance to the far clipping plane It defines the position of the back face of the viewing frustum far from the viewer Any objects placed beyond the far clipping plane will not be visible since they will be clipped Please refer also to the NearDist key description for more detail about the influence of clipping planes on depth buffer resolution Position This specifies the initial position of the viewer when the
56. the object was located at the midpoint of the eyes so that no position offset is needed We can specify a transformation between these two coordinate systems as follows GlassesXForm X 0 1 0 CameraX ViconY Y 0 0 1 CameraY ViconZ Z 1 0 0 CameraZ ViconX P 0 0 0 No position offset needed in this case 7 6 Scene This section contains various settings that determine which scene file is loaded by default and how it will be displayed within VRVision For example it is possible to enable a default light source to scale the scene and to automatically centre the scene at the origin The following section lists each key in bold text followed by a brief explanation File This specifies the name of the scene file to load by default It can be any suitable OpenInventor 2 1 or VRML 1 0 format file When VRVision is started from within Matlab without any parameters this is the file that will be loaded For example File scene iv Headlight This option can be used to enable a simple directional light source aimed along the Z axis into the scene If you wish to specify your own light sources within the scene file it is recommended that you disable this headlight For example Headlight 1 nable the light Headlight 0 disable the light 26 Scale This specifies the scale of the scene for display purposes If the object size is carefully defined and the scale and screen size are specified correctl
57. ts are as follows Operating System Windows 2000 recommended or Windows XP Matlab Version Matlab 6 1 or greater Optional Software Psychophysics Toolbox PsychToolbox The current version of VRVision has been developed on Windows 2000 and has also been used successfully on Windows XP Other versions of Windows such as 95 98 ME NT have not been tested and are not recommended The VRVision software is reasonably portable and we plan to develop versions for other operating systems MacOS X Linux in the future The development work was carried out in Matlab 6 1 and the software has also been tested in Matlab 6 5 Later versions of Matlab are probably compatible but are untested at time of writing It is recommended that you download and install the excellent PsychToolbox since this will give you the most flexibility when constructing experimental programs It is then possible to use PsychToolbox to display 2D images and user interface displays then use VRVision to display 3D scenes and for stereoscopic display as appropriate It would equally be possible to use the Matlab windowing system to construct user interfaces but you might find PsychToolbox more suitable for example it is difficult to make true full screen windows with Matlab 2 2 Hardware Requirements The hardware requirements are highly dependent upon which features of VRVision you wish to use The program should be usable in its basic form on most PCs However if you w
58. tton 0 or 1 pressed vrvis UseJoyQuitKeys any quit when any key pressed vrvis UseJoyQuitKeys 0 disable joystick quit If the user quits by pressing a key it is possible to find out the elapsed time and the key that they pressed using the following two functions GetQuitKey GetQuitKeyTime To distinguish the joystick buttons from any other key on the keyboard these functions return special names for each button ranging from JOYO through to JOYO UseFullScreen This allows you to select either full screen mode or to display in a window which can be moved or resized The default is to run full screen When running in full screen mode VRVision will force itself on top of all other windows Examples vrvis UseFullScreen 0 run in a window vrvis UseFullScreen 1 enable full screen UseUnderlay This function is used to enable a special underlay mode which causes the entire desktop contents to be screen captured as VRVision starts This screen capture is then used as a background image when drawing the 3D scene For example you can use the SCREEN function in PsychToolbox to draw some background graphics then enable the underlay mode and start VRVision When VRVision starts the 3D scene will appear superimposed on top of the drawing that you did previously Examples vrvis UseUnderlay 1 enable underlay mode vrvis UseUnderlay 0 disable underlay the default When und
59. vely halved so that flicker might be perceived by the user This can be avoided by increasing the vertical refresh frequency of the monitor However the maximum frequency available will depend upon the display resolution For example a monitor may support 100Hz refresh at 1024x768 but only 75Hz at 1280x1024 Therefore you will need to decide what resolution and refresh rate you need before selecting a monitor Increasing the vertical refresh rate will decrease the flicker The maximum vertical refresh rate is usually limited by the monitor rather than the graphics card You should aim to have a vertical refresh rate of at least 100Hz preferably 120Hz if possible Also it is not recommended to drive a monitor outside the limits recommended by the manufacturer since this can result in permanent damage Finally you will see a reduction in brightness when viewing stereo images when compared to mono images This is due to the attenuation of the LCD shutter which does not become perfectly transparent when open and since each eye will be exposed to the image for only 50 of the time the LCD shutter is opaque for the remaining time In an experimental study that compares mono and stereo viewing this will need to be considered 8 2 Graphics Cards This section describes some of the graphics cards that are suitable for use with VRVision and attempts to address some of the technical issues involved in using these cards Please note that the gr
60. y a brief explanation Deadzone Most joysticks are sprung so that the stick will return to a zero or centre position when released However they do not always return exactly to centre and may report a small non zero position value even when the user is not applying any pressure to the stick The Deadzone parameter allows you to specify a lower limit value below which the joystick movement will be ignored Increasing the Deadzone value means that the user will have to push the joystick further from centre before the scene will begin to move The acceptable range of the Deadzone value is between 0 and 1 but is typically a very small percentage of this range such as 0 1 This is because the full scale for the joystick movement is in the range 1 to 1 Therefore a Deadzone value of 1 would disable the joystick completely For example Deadzone 0 1 Some joysticks already implement this method at a driver level in which case a Deadzone value of zero can be specified to disable this feature in VR Vision Scale The scale parameter allows the sensitivity of the joystick to be adjusted Increasing the scale will cause the scene to move faster in response to the same amount of stick movement After clamping the joystick values within the Deadzone limits described previously they are multiplied by the Scale parameter to determine the rate of scene movement Therefore reducing the scale will make the stick less responsive and increasing it w
61. y in the INI file it is possible to display an object at actual size For example if the screen size is 40cm by 30cm and our scene file contains a 20cm cube then the scale can be set to 1 to display that object on screen at actual size Scale 1 However if scale is not important and you want the object automatically scaled to fit on the screen you can set the scaling mode to automatic Scale auto The scale factor is also commonly used to scale between units such as imperial and metric or to scale an object relative to the original size in the scene file for example Scale 0 5 AutoCentre If an object described in a scene file is to appear at the centre of the screen it should be located at the origin 0 0 0 since the origin in VRVision is located at screen centre However not all scene files will necessarily be defined to lie at the origin The AutoCentre option can be used to automatically move the scene to the origin when it is loaded This works by calculating the centre of the bounding box of the scene the smallest axis aligned box that completely encloses the scene and translating or moving the scene by that amount so that it is relocated at the origin For example AutoCentre 0 don t move the scene AutoCentre 1 move the scene to the origin Note that the scene will also rotate around the origin when using joystick or mouse movement functions This option can then affect whether an object will rotate about the origin of t

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