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1. the param eters specified when DYNAVIS is started The format of the parameter configuration file can be seen in this example Platoons 2 Cars 4 Relative 0 Position_ X 1 Position Y 0 Velocity X 1 Velocity Y 0 Accel avail 1 Jerk avail 1 The values we used in the example happen to be the default values assumed by DYNAVIS if the parameter file is not supplied in the command line These values will also be used in the case that any one of the parameters is not specified in the parameter file The syntax rules are very simple The parameter name has to be at the beginning of a line followed by an equal sign followed by a space and an integer value The variable Platoons specifies the number of platoons of vehicles in the range one to three The variable Cars allows the number of vehicles in each platoon to be specified in the range one to ten The position of each vehicle may be specified as the absolute distance traveled from the beginning of the simulation or as a relative distance between vehicles The variable Relative should be set to 1if the file contains relative distances or 0 otherwise The availability of a number of state variables such as X axis position Y axis position X axis velocity Y axis velocity acceleration and jerk has to be specified in order to match the format of the supplied data file This is done by setting a parameter value equal to 1 if the parameter is available in the data file and2. 0 if there is no corresponding field in the data file Appendix B Dynamic Visualization of Two Pla toons of Four Vehicles As an example we will describe how to set up and run a visualization session in the case of two parallel platoons with four vehicles in each Let us denote the position velocity acceleration and jerk of vehicle j in platoon i by pos vel acc and jrk respectively 1 Make sure that the input data file is in ASCII format Data for each variable has to be stored column wise in the file and the variables should be saved in the exact order shown below with space delimiters between fields time posts posyyn velyy acci Jrky post posyiz Veliz accy2 Jrkiz poszi3 posyiz velig accys jrky3 posti4 posyr4 velja accia Jrkis pOosS 22 posy22 Velzz accr2 jrkz pOst23 POSY23 velzz acces Jrka3 postr posyr4 Velz4 accz4 Jjrkz4 newline character 0r0A 2 The initial positions of the vehicles in the platoons are not pre specified They are found in the data file But the parameters that define the de sired positions have default values At the beginning of a visualization session the time headway and fixed headway parameters may have to be adjusted from the menu In files with relative position data the distance is measured between the front bumper of a vehicle and the rear bumper of the leading vehicle All the vehicles in the visualization environment have been assumed to be four and a half meters long and the user shoul
3. This paper has been mechanically scanned Some errors may have been inadvertently introduced INSTITUTE OF TRANSPORTATION STUDIES UNIVERSITY OF CALIFORNIA BERKELEY DYNAVIS A Dynamic Visualization Environment for the Design and Evaluation of Automatic Vehicle Control Systems A Kanaris Zexu J Hauser California PATH University of California Berkeley November 1994 PATH TECHNICAL NOTE 94 8 This work was performed as part of the CaliforniaPATH Program of the University of California in cooperation with the State of Califor nia Business Transportation and Housing Agency Department of Transportation and the United States Department of Transportation Federal Highway Administration The contents of this report reflect the views of the authors who are responsible for the facts and the accuracy of the data presented herein The contents dono necessarily reflect the official views or policies of the State of California This report does not constitute a standard specification or regulation DYNAVIS A Dynamic Visualization Environment for the Design and Evaluation of Automatic Vehicle Control Systems A Kanaris Z Xu J Hauser Southern California Center for Advanced Transportation Technologies EE Systems EEB 200B University of Southern California Los Angeles CA 90089 2562 Abstract DYNAVIS is an interactive engineering environment developed specifically for the design and evaluation of automatic longitud
4. ample jerk data is not available from simulations in many cases Sincejerk is directly related to the comfort of passengers and the quality of the ride it is important to visualize this parameter Thus we must build a post simulation data processor to estimate the jerk from position velocity and acceleration information In order to have a good visualization of all the parameters mentioned above an effective user interface is very important It is one of the major components of the design of DYNAVIS It is also one of the main reasons why the dynamic visualization system is much more advanced than an animation system When a user uses our dynamic visualization tool to visualize the dynamics of platoons of vehicles he should be able to O set up a graphic representation of the static scene ie number of platoons number of vehicles per platoon the parameters to be visualized etc O stop at any interesting scene O run the scene backward and then forward examining how things lead up to the situation O review a particular interval of time over and over again O change the time and space resolution arbitrarily These interactive user interface abilities provide users with a comprehensive con trol over when and how to replay a given scene and the ability to home in on the precise moment of interest in a timely and effective manner At the same time the user can be hinted by the correlation between various display components for the u
5. ce is implemented using the OSF MOTIF widgets and gadgets In the current stage of development DYNAVIS is already equipped with most of the basic functions required by a dynamic visual ization system We have already used it to analyze the dynamics of vehicle platoons The data sets came from both simulations and experiments We have also used it to evaluate vehicle control laws and had some very useful results For example we have used it to compare two automatic control laws One control law was using acceleration information from the leading vehicle and the other did not use this in formation By monitoring the position speed acceleration and jerk we easily found that both controllers achieve similar position and speed performance but the one without knowledge of the leading vehicle s acceleration resulted in smaller jerk These actual application tests show that dynamic visualization is a very useful tool for the analysis of the complex and highly coupled dynamics of vehicleplatoons Inthe future we anticipate using these and other forthcoming enhancements in DYNAVIS to design even better controllers for vehicle platoons 4 Desirable Enhancements We have thought of many further enhancements that are possible for DYNAVIS which will make the environment a more powerful and flexible tool O Enhance the support for lane change maneuvers through the already avail able lateral position specification The objective is to allow the user to b
6. d Interactively modify the zoom factor by selecting the length of the road to be displayed This allows the viewer to focus on a section of the platoon instead of getting an overall helicopter view In the current version of DYNAVIS we have the leading vehicles appear in fixed positions in each platoon and use the movement of road markers and the relative motion of the following vehicles to visualize the changes in vehicle velocity This enables us to visualize the platoons with good space resolution e Change the spacing between the road markers This gives the user a reference point by which he can sense and even measure distances with ease unparalleled in the real world e Change the program configuration by modifying a parameter configuration file This file is a plain ASCII file where the user can specify the desired traffic configuration in terms of number of platoons displayed and number of vehicles in each platoon DYNAVIS must be aware of the format of the data file been supplied to it for visualization This is achieved by specifying which fields of information are available from the data file and which fields are not available but have to be estimated instead All this information can be specified in the parameter file otherwise DYNAVIS will assume some meaningful defaults The description of the parameter file and the default parameter setup can be found in the user manual in the Appendix In DYNAVIS the effective user interfa
7. d observe this specification when generating the data file 3 Note that since we typically use two or more lanes to compare different control schemes the position and the dynamics of the leading vehicles in each platoon are assumed to be the same Hence we do not require and do not expect to find data for the leading vehicle in the second or third lane i e we do not save the data for posta velz accy jrko1 posts vels etc If the positions and other data for the leading vehicles in the other lanes are not the same the program code and associated data structures will have to be modified 4 To start running the program type dynavis datafile parameterfile 10 at the UNIX prompt After a few seconds the outline of a window will appear Use the mouse to move the outline window to any point on the screen Click the left mouse button to open the window at the desired position Use the middle button to adjust the window s position after it is opened At this point you should see the initial scene of a section of highway and the vehicles on it along with the meters corresponding to each vehicle The top row of meters indicate velocities Colored needles in the meters Red green and blue correspond to the cars of the same color The middle row of meters indicate acceleration and the bottom row of meters indicate the jerk 5 To stop the program move the mouse pointer to the menu section and click on the Command option then highl
8. decide what needs to be visualized and how to visualizeit After some study we focused on a basic set of capabilities that a dynamic visualization system should have In this section we describe these specifications and discuss the issues involved in the design of a dynamic visualization environment for automatic vehicle control systems These specifications have served as the guidelines during the design phase of the dynamic visualization system The dynamic visualization system is required to display the dynamics of individual vehicles or platoons of vehicles Therefore the following basic parameters should be visualized Parameters representing the dynamics of individual vehicle namely position ve locity acceleration and jerk Parameters directly related to the performance of the controller such as the de sired position of the vehicle and the position error Parameters representing the dynamics of the platoon or a group of vehicles for example the string stability Parameters directly related to human factor issues such as the quality of ride etc Typically we get explicit data for vehicle position and velocity and sometimes acceleration from the simulations or the experiments However data for some other parameters may not be directly available Thus the dynamic visualization system should include some data processing algorithms to estimate the missing parameters from the data set provided by the simulation or experiment For ex
9. e necessary information we can also visualize acceleration and jerk This is done by looking at the heads of the driver and passenger in each car through the glass sunroof of the car The driver holds the steering wheel so his head is straight during constant acceleration but it moves if it is subjected tojerk We assume that the passenger cannot anticipate any changes in vehicle velocity The passenger s head moves backwards when the vehicle is accelerating and forward when the vehicle is braking like a mass suspended from a spring This assumption allows us to get a feeling of what it would be like if we were inside the vehicle we are observing For a more accurate reading of vehicle velocity acceleration and jerk there are analog and digital meters associated with each vehicle The position of the meters is such that identifying the meter corresponding to each vehicle 5 can be done at a glance The rightmost meter corresponds to the rightmost vehicle in the platoon Each analog meter has three pointers each one of which corresponds to a car in each lane The color of the pointer is the same as the color of the vehicle it corresponds to This facilitates making quick comparisons of the performance of the controllers in different lanes of traffic Evaluate the performance of the controller by indicating the desired position of each vehicle The ideal or desired position is a function of the control law chosen for example time headway or c
10. e reviewed in real time or slower or faster than real time as chosen by the user Also it can accept data with non uniform time steps To help the user better understand the complexity of the dynamics of platoons of vehicles the dynamic visualization system must offer the ability to magnify the behavior of interest This is another reason why this system is far beyond basic animation systems To explain this let us consider the dynamics of a given vehicle in a platoon Assume that this vehicle is automatically controlled and denote the position of vehicle i at time by 2 the desired position of the vehicle by s t and the error by e t s t z t DYNAVIS can be used to visualize e t but since e t may be very small compared to other geometries on the scene its visual impact would be limited and detecting its presence may not be easy Instead one can visualize ae t where is a on line changeable number and thus facilitate the observation of position errors in controller performance the effects of nonlinearities or any other relevant system characteristics with the appropriate resolution 4 Since DYNAVIS is designed to visualize numeric data describing the dynamics of vehicle platoons it mainly accepts and processes data from off line simulations and experimental data captured during in vehicle tests However on line simulation in DYNAVIS is also desirable If the dynamic visualization environment has on line si
11. ensional with provision to specify the viewpoint and the viewport Extend the system with scenery files in order to allow for the highway to have turns and uphill and downhill sections Extend the format of the data files to include vehicle position in the vertical direction O Study the possibility of integrating some limited simulation capabilities in the visualization environment and its negative impact on visualization speed and flexibility Appendix A DYNAVIS User Manual Make sure that dynavis the current version of DYNAVIS is in your current path or directory and start execution by typing dynavis datafile parameterfile The first argument is the user supplied data file If it is not provided dynavis will refuse to run and instead will print the correct syntax for invoking DYNAVIS The second argument is the name of the optional but recommended parameter configuration file The data file provides all the position velocity acceleration and jerk information for each vehicle in each time step All the data for a single time step has to be in one line since the program searches for the newline character to parse the data file The first item on each line must be the current time step value followed by the data fields The only delimiter allowed between data is one or more spaces The visualization program makes very few assumptions about the data itself The parameter file is not strictly required but it is preferable to have all
12. etter visualize the lateral dynamics of the vehicles during lane changes QO Devise a mechanism to obtain acceleration and jerk information for purpose of visualization when the data set does not provide such information This may be achieved by appropriate filtering of available vehicle data O Enhance user friendliness and interaction by adding help screens parameter input menus and dialog boxes OQ Add MAX and MIN memory capability to the meters Extra pointers on the meters can indicate the maximum and minimum data value reached during a visualization session The feature can be turned on and off by a radio button selection O Add the ability to set the limits beginning and end of a time period of in terest and repeat this interval over and over again to allow the user to choose different speeds and magnification to study a particularly interesting portion of the animation Currently the user has to pull back the Time Index slider knob every time he wants to review a specific time period Q Address some human factor issues in the visualization such as devising indica tors for the comfort level and quality of the ride and some appropriate means of displaying them O Provide some means of choosing interactively the scenarios for visualization The user should be able to specify and load a new data file at any time during a visualization session without having to stop and reload DYNAVIS Make the visualization environment three dim
13. hich best brings out the subtleties associated with the dynamics Since the time resolution is determined by the time step used in simulations or experiments in order to increase the resolution we have to know the data information at other time instances between the time interval in the original data In this case an interpolation technique has to be used Employing an interpolation technique is also crucial when the data provided to the environment has non uniform time steps This may happen when automatic step sizing is used to find the solutions of a set of differentialequations by some simulation software package like Matrix X Simulinkor MATLAB Furthermore sometime steps in a non uniform time step case may be too large to generate real time graphics Consequently without interpolation visualization would not convey the appropriate time dependent properties of the system to the user The interpolation technique to be used could be linear quadratic or any other nonlinear technique Using linear interpolation is well justified when the time step in the original data is small enough since parameters of the dynamics of vehicles can be considered to be differentiable and differentiability in effect says that locally parameters change linearly To summarize we have to use an interpolation technique in the dynamic visu alization system By employing this technique and considering the capabilities of the graphic workstation the dynamics can then b
14. ight Stop and release The vehicles and the meters will freeze 6 To restart the animation move the mouse pointer to the menu section click the Command option highlight Start and release the button 7 Use the scales at the bottom of the window to adjust the time step speed of animation shuttle to another point in time change the road length zoom factor magnify the position errors change the spacing between the road markers 8 To exit from DYNAVIS go back to the menu and choose the Quit option under the Command menu Appendix C Video Tape Demonstration We have created a video tape which shows an overview of the capabilities of the current version of dynamic environment and a sample session of using and interacting with DYNAVIS For a copy of this video tape please contact the authors at the University of Southern California Center for Advanced Transportation Technologies 11
15. inal and lateral vehicle control systems It can be run on any Silicon Graphics Workstation The capabilities of DYNAVIS go far beyond simple animation systems by providing a set of tools to perform inter active visualization with on line modification of many visualization parameters such as time and space resolution The capabilities of this program greatly facilitate de tecting undesirable phenomena in automatic vehicle following platooning designing and evaluating vehicle control systems and comparing the performance of different control strategies In this report we present the desired specifications of a dynamic visualization system discuss the issues involved in its design and describe the dy namic visualization system that we implemented A user manual has been included in this report We anticipate that our dynamic visualization system will be a valuable tool to designers of automatic vehicle following and platooning systems 1 Motivation Conceptual Overview When we do simulations or experiments we need an efficient method to analyze the generated data For example consider the simulated or experimental data for a platoon of four vehicles over a period of five minutes denoted by T with sampling time of 0 1 second denoted by t To study the qualitative characteristics of this system one might plot the position velocity and possibly acceleration and jerk of each vehicle versus time 16 plots overall Because of the high rati
16. mulation capability then the user can interactively specify the speed profile for the leading vehicle and create various scenarios and disturbances 3 The Dynamic Visualization Environment DYNAVIS was developed to aid in the design and evaluation of longitudinal and lateral vehicle control systems The current version of the program offers the user the following capabilities oO Q Visualize the dynamics of one to three platoons with up to ten vehiclesin each platoon The platoons are displayed side by side This parallel platoon envi ronment provides a convenient way of comparing the performance of different control laws For example we can easily compare the performance of an auto matically controlled vehicle platoon to a platoon driven by human drivers It also provides a convenient way of comparing the performance of two implemen tations of the same control law with different controller parameters DYNAVIS can easily be reconfigured to visualize one platoon only or two or three platoons with any number of vehicles up to ten in each platoon Visualize each vehicle s position velocity acceleration and jerk simultaneously The position of all the vehicles is displayed graphically on a simulated section of freeway with accurate scaling of their positions relative to the freeway lanes and vehicle size The velocity of the vehicles can be identified by the relative velocity of road markers Provided that the data set contains all th
17. n derlying cause of a given behavior In fact without an effective user interface visual engineering as discussed above would be an awkward task if one had to change and compile the program when a certain parameter had to be changed To develop this interactive user interface the programming paradigm had to be carefully chosen The development of an environment with the characteristics men tioned above depends heavily on the mode of programming chosen For example in procedural programming with a character based interface the application program is always in control while it is running In this case the application allows the user to give input only at certain pre specified sections of the program where multiple levels of menus should be traversed before a certain action can be taken Clearly this 3 programming paradigm is not suitable for development of a dynamic visualization environment In fact an event driven framework is necessary for this development where applications are embedded in an environment which prepares them to respond to many differentevents at any time In this paradigm the user is in control most of the time The application starts by setting up a static scene and then enters a loop from which different functions can be invoked when a designated event is queued As mentioned above an effective user interface should offer users the ability to change the time resolution arbitrarily Thus we should provide an environment w
18. o of T t and the lack of an explicit connection between these 16 plots it will be difficult and time consuming to understand the nature of the dynamics and to detect the undesirable system characteristics In a situation like this an efficient method is needed to analyze the data The dynamic visualization is such a method The main idea of dynamic visualization is to take advantage of a humans spatial intuition When we see some curves on paper we may not fully appreciate if the system behavior is good or not Some system characteristics may not be visible by looking at the plots However when we see a moving picture we can easily recognize the system performance based on our intuition Thus by transforming the numeric data into an animation we can examine large amount of data with better comprehension and efficiency This can be very helpful in the control design and evaluation Another reason that makes a dynamic visualization system not only useful but absolutely essential is the evaluation of system performance under worst case scenarios In fact by employing simulation and dynamic visualization costly and dangerous experiments can sometimes be avoided Next we are going to present the specifications of this dynamic visualization system and some details about the methods used 2 Development of the Specifications In the development of the dynamic visualization system we first had to determine the specifications of the system We had to
19. onstant headway It can be easily changed from the menu to implement different rules like California safety rule automatic control safety distance rule etc Start stop and replay the graphic simulation of the platoon dynamics at any point of interest The time step is adjustable over a wide range thus allowing the playback speed to vary from slow motion to fast forward Frame by frame advance is also available The time step of the animation can be changed by adjusting a slider knob on a logarithmic scale The data set does not need to include data points for every frame that can be displayed Data sets typically consist of only a few hundred frames and the time step does not have to be uniform DYNAVIS can display animations with apparent resolution of thousands of frames and with any chosen time step It achieves that by employinga linear interpolation technique to estimate data for time instances that fall between existing frames This in effect can reduce or increase the speed of animation since DYNAVIS updates the screen at a fixed frame rate regardless of the chosen time step This enhances the illusion of continuous motion as well as the apparent time resolution Change the scale by which any position deviations are magnified When the controller algorithm is nearly perfect the position error may become very small By magnifying any remaining errors the user can evaluate the performance of his design and iterate until he is fully satisfie
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