Wiley Maya Studio Projects Photorealistic Characters
Contents
1. 23 The left arm is next Use the following table to map it For the hand add an SC IK handle from wristLft_JNT to middlelLft_JNT The thumb on the motion capture skeleton is too awkward to include you can skip that joint SC IK Handle Point Constraint Orient Constraint ikHandle 8 lhumerus Iclavicle ikHandle 9 lradius lhumerus ikHandle 10 lwrist lradius ikHandle 11 lhand lwrist To check the alignment of the two skeletons go to frame 424 and compare it with Figure 1 28 To check your work so far you can compare it to mocap_v04 ma on the DVD 24 The head and neck are next 25 SC IK Handle Point Constraint Orient Constraint ikHandle 12 upperneck lowerneck ikHandle 13 head upperneck More than half of the character is constrained Unfortunately IK handles and con straints can t be mirrored You must manually assign all the bones from the right leg and arm You can continue or skip ahead to the following saved scene file MOTION CAPTURE 23 Figure 1 28 Check the align ment at frame 424 24 CHAPTER 1 CHARACTER SKELETONS 5 To check your work so far you can compare it to mocap_v05 ma on the DVD 26 Hide all the joints and handles Play the animation to check the quality of the motion Figure 1 29 shows Jack in an extreme pose at frame 550 Maintaining Performance Other than the obvious geometry collisions the data transferred pretty well The only major motion related issue is in the2. HIK MOTION CAPTURE 17 systems Until these are capable of delivering a convincing human performance we still need to rely on motion capture for the ultimate in photorealism As we mentioned at the beginning of the chapter it s important to know where your motion capture data comes from You can use material downloaded from the Internet but it often requires a lot of work and in the end produces less than adequate results To use motion capture to its fullest potential you must have complete control over every aspect from the actor to the data that the motion capture outputs With that said more and more websites offer motion capture data Using this data can save you a tremendous amount of work and the data is relatively cheap if not free Project Motion Test The Jack character is weighted but you don t know how he ll perform To test his abili ties you can apply downloaded motion capture data to his skeleton The data used in this project is from Carnegie Mellon University s Graphics Lab They have a larger motion capture database that you can access at http mocap cs cmu edu In addition they have numerous other resources like converters and documentation Follow these steps 1 Open the mocap_v01 ma scene from the chapter1 scenes folder on the DVD The scene ey contains the character s geometry weighted to his skeleton The geometry and skel eton have been assigned to respective layers A second skeleton is in
3. so the lower half of the body was neglected Again having video of the capture session can reveal where the markers were placed But videos may not reveal all them Not having their exact locations makes it difficult and sometimes impossible to determine the differential between the motion capture joint center and your CG character joint center All these reasons reinforce the need for your own personal motion capture studio Having your own setup gives you complete control over the data 8 CHAPTER 1 CHARACTER SKELETONS 5 Weighting Quaternion weighting helps skin deformations tremendously You no longer need addi tional bones to help support the volume of skinned parts you only need to add joints where your character needs them making the process far more intuitive This also helps with the weighting process Instead of the skin caving in at a bent joint the volume is maintained causing the skin to penetrate the opposing side You can coun teract the penetration by painting weight from the opposing side You can even mix the quaternion weighting with classic linear weighting to have the skin lose some volume in the area creating the illusion of collision Both options create a more lifelike fold in the deformation In the first project Jack is weighted to his skeleton using quaternion weight ing techniques Project Painting Weights Youve evaluated the geometry and built the skeleton Everything is in place for skin weight
4. To check your work so far you can compare it to shoulderFix_v01 ma on the DVD ey 9 You can work on painting the weights on the single mesh character or import the already fixed scene file weightFix_v01 ma from the chapter1 scenes folder A on the DVD 28 CHAPTER 1 CHARACTER SKELETONS Figure 1 34 Jack is now back in his default bind pose 10 11 12 13 The correctly weighted mesh is loaded into the scene The two versions of Jack over lap each other Turn off the layer visibility of the imported Jack nodes You can t copy the weights over to the animated Jack successfully until he is back into his bind pose Go to frame 13 0 on the timeline and choose Modify gt Evaluate Nodes gt Ignore All Now that everything is shut down select all of the animated Jack s joints A quick way to accomplish this is to choose Edit gt Select All by Type gt Joints You can then deselect the extra joints in the Hypergraph or Outliner With all of Jack s joints selected set their Rotation to 0 0 in the Channel Box Jack returns to his default pose without all of his IK handles see Figure 1 34 14 15 16 17 MOTION CAPTURE 29 You can turn on the layer s visibility for the correctly weighted Jack although doing so isn t necessary Shift select weightFix_v01_body1 and bodyl Using the default settings choose Skin gt Edit Smooth Skin gt Copy Skin Weights Shift select weightFix_v01_head1 and h
5. six times 14 Choose shoulderLft_JNT Change the Paint operation to Replace and use a Value of 0 0 Paint out all the weights up to the shoulder Use Figure 1 14 as a guide Remember to do the back of the character as well 15 You should start to see some progress At this point you can use the Smooth opera tion to refine the weighting Keeping shoulderLft_JNT selected smooth the weights around the shoulder area You should end up with weighting similar to Figure 1 15 16 Go through all the other joints and continue to smooth the weights around the shoulder The shoulder will look pretty good when youre finished This is a good time to save your scene ey To check your work so far you can compare it to jackWeights_v02 ma on the DVD 17 With the shoulder basically finished let s move down the arm Select elbowLft_JNT and rotate it 30 0 units in the Y Chat Figure 1 14 Figure 1 15 The weights for shoulderLft_JNT Smooth the weights for shoulderLft_JNT 18 19 20 2l 22 23 24 ZO WEIGHTING 13 Select the character s geometry and open the Paint Weights tool options Select the following joints from the Influences list and pin the selection e clavicleLft_JNT e shoulderLft_JNT e elbowLft_JNT e radiusLft_JNT e wristLft_JNT Click shoulderLft_JNT Replace any weighting with 0 0 below the elbow Switch to elbowLft_JNT and replace all the weights above the elbow with 0 0 Repeat for radiusLf
6. CHAPTER 1 Character Skeletons Getting al character to move properly begins and ends with a good skeleton It takes proper positioning and the right number of joints The skeleton pro vides functionality and at the same time limits the ways geometry can deform In this first chapter you ll construct a skeleton and weight it to a modeled character You ll then apply stock motion capture to test the character s deformations and the skeleton s validity In this chapter you will learn to Evaluate your characters geometry Paint weights Mirror and copy weights Apply motion capture Use the FBX file format 2 CHAPTER 1 CHARACTER SKELETONS Character Pipeline The details of a character pipeline vary based on the character and change from company to company and artist to artist but for the most part the overall process doesn t change In this book the pipeline is as follows PHOTO REAL PIPELINE bt Establish the geometry Build a skeleton with basic functionality Add traditional skin weighting Create the facial anatomy Set up skin simulation Add facial hair using Fur Create and style hair Dress the character O e ce A Implement secondary character effects jt Capturing a performance jt bp Add lighting and rendering Traditional skin weighting or binding only goes so far The character in this book is fully clothed therefore his body doesn t need intense skin deformations But t
7. Handle2 Add a point constraint Shift select upperback from the motion capture skeleton and ikHandle2 Add an orient constraint To finish the spine add an SC handle from spine2_JNT and collar_JNT Shift select lowerneck from the motion capture skeleton and ikHandle3 Add a point constraint Shift select thorax from the motion capture skeleton and ikHandle3 Add an orient constraint For the left leg follow the same procedure all the way down the skeletal chain Here is a list of the constraint mappings SC IK Handle Point Constraint Orient Constraint ikHandle 4 Itibia lfemur ikHandle 5 lfoot Itibia ikHandle 6 Itoes lfoot ikHandle 7 Itoes_end Itoes Point Constraint Options Edit Help Point constraint Sp Ly Offset o awaa 0 0000 0 0000 animation Layer Mone Set layer to override w Constraint axes w All Weignt 1 0000 T Orient Constraint Options Orient constraint Edt Help Mantainoffssh a Animation Layer Mone Set laver to override w Conshraint aves w Al Wagt 1 0000 Figure 1 25 Figure 1 26 Two constraints are used to align a single bone Point and orient constraint options 22 CHAPTER 1 CHARACTER SKELETONS 22 Now isa good time to check and save your work Jack s skeleton should look like Figure 1 27 at frame 280 Figure 1 27 Check the align ment at frame 280 ey To check your work so far you can compare it to mocap_v03 ma on the DVD
8. Maya isn t good enough The data may be missing keys or the actor s physique may be the oppo site of your character As mentioned earlier it s possible to use differently proportioned skeletons but not knowing why the data moves the way it does is a huge impediment The rotation of a joint isn t a good representation of the joint s position This is especially true for incomplete data sets like hands Capturing finger motion is difficult so the hand is sometimes a single joint or made up of a hand and a thumb joint Regardless the twisting motion of the wrist and upper arm is difficult and sometimes impossible to decipher without having a video reference of the actor Remember the skeleton must be calibrated first before the motion can be applied properly If you can t align your character to the motion capture skeleton you ve already lost the battle Another issue with motion capture data is frame rate Most capture sessions are done at 60 fps or higher to help in the tracking process This is especially true for quick actions A higher frame rate helps the software accurately track the data It also helps when mark ers become obscured Having more frames allows you to interpolate through the missing track points more smoothly The third problem with downloaded motion capture is the number of joints and marker placements Motion capture is done for different reasons The downloaded ses sion may have been to get arm data only
9. Mover you track points that are identifiable in all the camera views The points in the footage are typically markers that were manually placed for the sole purpose of track ing MatchMover turns these markers into points in 3D space see Figure 1 7 The track points are then used to derive an animated skeleton by literally connecting the dots Figure 1 8 The track points are exported to Maya In Maya multiple skeletons are created and connected to each other Scale plays an enormous role no pun intended in setting up both rigs Scale is addressed in detail in Chapter 7 Performance Capture The motion capture skeleton and data aren t the critical part of the pipeline The skel eton can change and the data can change It s what you do with the data that is decisive With that said you can t use any old data For instance there is a lot of downloadable CHARACTER PIPELINE 7 motion capture data Getting such data to work on your character is possible as shown in the last two projects in this chapter but it often fails for numerous reasons ia igure 1 First downloaded motion capture data may fail due to The track points are linked together to form a skeleton unknown factors You don t know how the data came to be The actor s physique doesn t need to match your character but knowing what the person looked like is helpful Having a video of the actual performance is invaluable Seeing the motion on joints in
10. ONS Figure 1 24 The captured char acter squats down with Jack s root node connected and perfectly aligned Click Play to see the constraints working Figure 1 24 shows that the two skeleton roots are nicely aligned Tyr Wy p To check your work so far you can compare it to mocap_v02 ma on the DVD Let s take a moment to review what you ve just done You point constrained Jack s root node to the motion capture root node You only point constrained the root node none of the other joints are directly constrained Then you created an SC IK handle from Jack s root to his first spine joint You point constrained the SC handle to the motion capture s second spine joint upperback Doing this locked the Y and Z rotation of Jack s root joint to the pitch and yaw of the motion capture skeleton Next you applied an orient constraint to the SC handle effectively locking the X rotation to the twist of the motion capture skeleton The formula is to point constrain the SC handle to the top of the bone and orient the handle to the root of the bone Figure 1 25 illustrates 14 I5 16 17 18 19 20 2L MOoTION CAPTURE 21 Return to frame 13 You can now begin adding handles and constraints to the rest of the joints For quick reference Figure 1 26 shows the point and orient constraint options Add an SC handle from spinel_JNT to spine2_jnt Shift select thorax from the motion capture skeleton and ik
11. The shoulders at frame 1 UPDATING CONSTRAINTS When you move the clavicle the arm moves away from the motion capture skeleton it s con strained to The constraints aren t broken they simply don t update To force the constraints to update move to a different frame and then move back to frame 1 the arm will now be in the proper position 5 Even without a rotation on the clavicle it s too high based on the position of the arm Rotate it to 7 0 units in the Z You can see the results in Figure 1 31 26 CHAPTER 1 CHARACTER SKELETONS Figure 1 31 The shoulder has been rotated in the Z by 7 0 units 6 Shift select lclavicle and clavicleLft_JNT Choose Constrain gt Orient Add the con straint with the settings from Figure 1 32 Figure 1 32 Orient constraint T Orient Constraint Options Edt Help options Maintain offset Animation Laver Set laye Lonstraink axes Weight 1 0000 MOTION CAPTURE 27 7 After evaluating the shoulder again with its new orient constraint it becomes evident that there are weighting issues compounding the problem You can see in Figure 1 33 that clavicleLft_JNT is too strong of an influence Figure 1 33 ClavicleLft_JNT weights 8 You don t want to paint the weights on this model Doing so would break the smooth blending between the head and body Instead return to the single mesh weighted character to perform the fix Before proceeding save your scene file
12. ase also demands a more intricate setup In this book the character you ll create is clothed Most of his skin is covered only his hands and face are exposed As a result his body can have basic deformations while his face is complex Figure 1 1 shows the geometry of the character named Jack who is the focus of this book Figure 1 1 Jack s geometry The geometry s density is consistent across the entire surface Using predominantly quadrangle polygons funnels the edge flow from the body and arms up into the head The head which is significantly smaller than the overall body benefits from compact ing the incoming geometries into less space Therefore you have a good balance of geometry to support simulated clothing over the body and detailed deformations on the exposed face You use a muscle based rig to drive the face Blend shapes or morph targets are often used to animate facial expressions However they generate unnatural motion between each target and cause the development artist to generate hundreds to thousands of shapes to counteract the effects of the process Muscle rigs make sense Real muscles move in a linear fashion and replicating this motion in computer graphics CG is simple The 3 4 CHAPTER 1 CHARACTER SKELETONS Figure 1 2 The interior of Jack s mouth combined motions of groups of muscles create a facial expression Tweaking this expres sion is a matter of moving a muscle a little up or a lit
13. ck Save Preset and call it mocap You can call the preset anytime you need to export another motion 14 Click Close to exit the Edit Export Preset window The Export All Options window is still open Click Export All to save the file It s a good idea to create a directory named FBX in your project directory to keep things organized ey 15 Open the shoulderFix_v02 ma scene from the chapter1 scenes folder on the DVD 16 Choose File gt Import and change File Type to FBX Also deselect Use Namespaces and use the settings shown in Figure 1 43 T import Options Edt Help General Options Group Remove duplcate shading networks File Eype FBR ka gare Version Y Referencing Options Preserve references Load Settings Load al references Y Name Clash Options T e strongy recommen to resoke Mame Clashes EEE por ame Functionality will rat be OF may mat work File Type Specific Options Edit preset Import Save and dose Cancel 17 Click Import to go to the Import browser window Select the boxing fbx scene from the chapter1 FBX folder on the DVD As soon as you select the file the FBX options appear at right in the window 18 Under Include change File Contents to Update Scene Elements Make sure Animation is selected and use the settings from Figure 1 44 Y Animation Animation w Extra Options Animation Take Take O01 Fill Timeline a Bake Animation Leyers Optical Merkers Quatermion Interpo
14. e between the default weight maps and the colored ones 9 10 CHAPTER 1 CHARACTER SKELETONS Figure 1 11 The black and white based weights maps are on the left and the colored heat maps are on the right 8 10 GRADIENT WEIGHT MAPS There are two ways to display a joint s influence grayscale shading and color ramps also known as a heat map The grayscale shading is straightforward black is zero and white is one Heat maps increase the amount of visible contrast by displaying weight values as colored intensi ties They facilitate the ability to paint without knowing the actual value of the weight In other words you can paint with greater accuracy You can also see variants in the weighting that wouldn t normally be noticeable in traditional grayscale maps such as values in the hundredths The first objective in the weighting process is to remove all the unnecessary weights You could begin by choosing Skin gt Edit Smooth Skin gt Prune Small Weights but this can also remove some necessary weighting Instead using the heat map you can easily paint out what you don t need Select radiusLft_JNT from the Influences list The radius shouldn t have any effect on the skin past the elbow Using a Replace value of 0 paint out all the blue weights up to the elbow Select elbowLft_JNT from the Influences list and remove all of its blue values up to the elbow as you did for radiusLft_JNT in step 8 Do clavicl
15. eLft_JNT next Remove all the weights except a large area around the upper shoulder Use your own body as reference Place your hand over your heart and then raise your shoulder Feel the skin move Slide your hand down and around the bottom of your ribcage Keep raising your shoulder to feel how far the effects of the clavicle go Figure 1 12 shows the remaining weight values I1 12 WEIGHTING 11 Don t worry about getting the weights perfect or taking away too much The weights are far from being finished and it s much easier to come back with the Smooth Paint operation to fine tune the results Spine2_JNT is a little out of hand Its influence spreads across most of the body Instead of trying to paint this out it s easier to flood the weight to 0 and paint it from scratch Change Paint Operation to Replace set Value to 0 0 and click Flood All of its weights are removed Change Value to 1 0 and change Brush Profile to the Solid brush Paint from the bot tom of the breast to just under the collar bone Go from the center of the chest to the center of the back Use the edge flow of the geometry as a guide There is no need to paint the right side because you ll eventually mirror the weights Use Figure 1 13 as a reference Figure 1 12 Figure 1 13 The weights for clavicleLft_JNT The weights for spine2_JNT 12 CHAPTER 1 CHARACTER SKELETONS 13 Switch the Paint operation to Smooth and click the Flood button
16. ead1 Choose Skin gt Edit Smooth Skin gt Copy Skin Weights Turn all the nodes back on by choosing Modify gt Evaluate Nodes gt Evaluate All Jack snaps back into place with new shoulder weights see Figure 1 35 To check your work so far you can compare it to shoulderFix_v02 ma on the DVD ey Figure 1 35 Jack looks bet ter with his new weighting 30 CHAPTER 1 CHARACTER SKELETONS 5 FBX The FBX file format has a long history of exchanging hands It s ironic because it s labeled as a universal data exchange format The name is from its original owner Filmbox After numerous ups and downs Filmbox eventually became MotionBuilder now owned by Autodesk Its current version is now supported by Maya 3D Studio Max Softimage LightWave and others including a QuickTime format Project FBX Import In this project you ll use the FBX file format to export and import a motion onto Jack Here are the steps 1 Open the boxing_v01 ma scene from the chapter1 scenes folder on the DVD The scene file Figure 1 36 contains The skeleton takes a skeleton i alin with boxing motion The timeline has been set to the beginning and end of the motion The skeleton was derived from the same actor who provided the motion for the exercise routine in Project Motion Test You can see the skel eton taking a punch in Figure 1 36 2 Select root from the Outliner and group the skeleton to an empty gro
17. erformance capturing is an important element in the photoreal character pipeline Part of this process is cre ating a capture skeleton You want the skeleton to match your character s skeleton as closely as possible The more it deviates the harder it is to transfer its motion There will inevi tably be some difference but it s possible to calibrate to different skeletons Figure 1 4 After testing several positions the locations of the hip and knee are determined Figure 1 5 Joints are positioned based on the shape of the hand and fingers 5 6 CHAPTER 1 CHARACTER SKELETONS Figure 1 6 The interface for Autodesk MatchMover Figure 1 7 Markers from the imported foot age turn into track points in 3D space To maintain the freedom to design and build any character you need a system for calibrating the two rigs The better your calibration process the greater your freedom The capture skeleton is based on the actor whose performance youre capturing For this book the capture skeletons are generated using Autodesk s MatchMover program see Figure 1 6 Many other tracking applications are available that you can use in place of MatchMover Autodesk s MatchMover program offers the benefit of compatibility Because it s an Autodesk product files can be exchanged between Maya and MatchMover easily After you import multiple angles of video or film footage of the same action into Match
18. formed Models Deformed Models Figure 1 40 The Deformed Models section of the FBX options 32 CHAPTER 1 CHARACTER SKELETONS 11 The rest of the Animation options should be turned off Curve Filters and Constant Key Reducer are useful for cleaning up animation curves but at this point you aren t interested in cleaning the curves Geometry Cache Files and Constraints the next two sections have no bearing on the scene because none of these objects exist in the scene Figure 1 41 shows all the settings Figure 1 41 The remaining Curve Filters Animation options Curve Fibers Constant Key Reducer Constant Key Reducer Tracslacion Preceion Geometry Cache File s Geometry Cache File s Constraints C r saints FBI Definitions 12 The only other parameters that need mentioning are under Advanced Options the Units and Axis Conversion sections shown in Figure 1 42 Figure 1 42 The Units and Axis ones Conversion sections Sq SPS of the FBX options Automatic Fie units converted fo Centimetr Asis Conversion Fk UT 7 FBS File Format Type Binary version FES 2011 Compatible with Autodesk 2011 applications and 2011 Fes plug ins None of these need altering but they re important if you re exporting to a different software package or want to convert the units through the export You can also set the file format to ASCII giving you the ability to edit the output by hand 13 Cli
19. he charac ter needs to act He needs to be able to speak and be convincingly expressive To achieve this level of realism it s crucial to match the real world as much as possible Driving the character s face is an anatomically correct muscle system The muscles squash and stretch and push and pull on the skin like real muscles Replicating human anatomy is half the battle The muscles may move perfectly by themselves but it s a different story when you need all of them to work together to form a smile or a frown In comes performance capture The term was coined by James Cameron while working on Avatar Performance capture is the recording of every movement made by an actor Well maybe not every movement but enough motion to identify speech expressions and of course full body activities Skin Evaluation Prior to adding joints you should always evaluate your character s geometry or skin It should have proper edge flow and enough faces for detailed deformations Computer speed is constantly on the rise Thanks to more RAM and accelerated GPUs software has been able to increase production complexity In the past numerous techniques were used to push as much of the character s geometry as possible off until render time This is still practiced today but you can add more geometry to the character s actual bind The CHARACTER PIPELINE increase makes it possible to have deforming wrinkles and folds with accurate collision This incre
20. in already If they aren t check the scene and enter the appropriate numbers see Figure 1 39 Resample All is optional Selecting it redoes all the keyframes Ultimately you aren t using any of the keyframes on this skeleton youre only copying its motion so the keyframe positions don t matter But if you like or possibly foresee the need to look at the animation curves this option is very useful The original boxing motion was captured at 120 fps and reduced in Maya to playback at 30 fps This forces the keys into fractional frame numbers Resampling the animation through the FBX export puts a keyframe only on integer frame numbers You can deselect Deformed Models in the Deformed Models section The parameter doesn t apply because there isn t any geometry in the scene see Figure 1 40 5 Figure 1 37 Set the Export All options to export FBX ioj xi T Export All Options Edt Halp General Options File type FRR export ha Defaut fle extensions Preserve references Export unloaded references File Type Specific Ophions Edit preset Save and Jose Export All Animation Snmeton w Extra Options Use Scere mame Remove sn ge ke y Quabermion Interpolation Mode Resample 45 Euler Interpolation Figure 1 38 The Extra Options section of the FBX options Bake Animation Bake Animation tert 2 Figure 1 39 The Bake Animation section of the FBX options De
21. ing All of Jack s weights are done with quaternion weighting The geometry to be weighted is one complete mesh Ultimately the mesh is divided into two pieces but it s easier to weight a single mesh and then copy the weights to the final broken up mesh The following tutorial takes you through the entire process 1 Open the jackWeights_v01 ma scene from the chapter1 scenes folder on the DVD The scene contains the character s geometry as a single mesh and his skeleton The geom etry and skeleton have been assigned to respective layers 2 Open the Outliner and Ctrl select the root_JNT node and the jack node Choose Skin gt Bind Skin gt Smooth Bind tool options 3 In the default settings change Skinning Method to Dual Quaternion Use Figure 1 9 to confirm your settings Click Bind Skin to accept the options The default bind does a decent job of weighting the character It s far Edt Help Bind bo Joint hierarchy from perfect of course but it pro a vides you with a clear path Most of Skinning method Dual Guatsmiom Mormalize Weights Past the needed corrections center on the R sie Mex influences 5 l gt torso Figure 1 10 shows the torso s SE ae Cropotfrebe 4 0 ci deformations w Remove unused influences w Colorize skeleton 4 Select clavicleLft_JNT and rotate it to 15 0 in the Z Select shoulderLft_ Apply JNT and rotate it to 45 0 in the Z Figure 1 9 Change the Smooth Bind o
22. ion You can feel a similar effect by trying to stand still All of your muscles fire to maintain your position A single muscle applying force to a bone causes a chain reaction of hundreds of micromovements Some go unnoticed but when they re missing we instantly recognize that something is wrong It s extremely difficult to calculate all those small motions and apply them in an animation However that s not the hard part The real trick is finding the tim ing and patterns that exist among those motions Look at Figure 1 20 it shows an excerpt of a motion captured actor doing jumping jacks The top curve is the Y axis of the wrist The middle curve is the X axis from the radius and the bottom is the X axis of the humerus bone Jumping jacks produce strong deviations in all the curves but pay attention to how each curve has a relationship to the other Even though they share the same peaks and values how they get there isn t the same Jitters and hiccups along the way indicate one bone supporting the other You can see how the motion becomes seemingly more erratic as you go from the larger parent bone on top to the smaller child bone on the bottom aa Someday computer generated rigs will have this f d motion built into them allowing animators to choose key l positions and synthetic anatomy to fill in the rest We re a j not far from having this technology Maya has a precur l sor with full body IK FBIK rigs and human IK
23. it Smooth Skin gt Copy Skin Weights The weights successfully copy over to the two separate pieces as if they were weighted together You can now delete the jack node To check your work so far you can compare it to jackWeights_v06 ma on the DVD ey 16 CHAPTER 1 CHARACTER SKELETONS Figure 1 20 Three axes from motion captured data Motion Capture Even the best animated characters still fall short of captured motion You just can t beat the real thing There are reasons why but current hand keyed animation isn t as convinc ing Movie producers like to say it s because animators make characters do things that aren t natural Animators say they needed more time or better direction The truth is the problem lies in the intricacies of the human body and the inadequacies of the current tools To put it another way it s bad timing When people and animals move each bone is influenced by the one before it This of course is inverse kinematics IK However when one bone moves the others counteract Imagine typing on a keyboard Your palms are resting on the desk and it seems as though your fingers are doing all the work with your wrist keeping things stabilized In order for your wrist to keep your fingers on the key board your elbow shifts periodically To sup port that elbow motion your shoulder compensates It doesn t stop there every time you peck at a different key different muscles are called into act
24. lation Mode Flesamole As Euler Interpolation Probeck Driven Keys Beforming eements bo joints w Update Pivots from Mule w Geometry Cache File s 19 Click Import in the browser 20 The motion loads and the Jack character is updated He now moves with the boxing motion capture Figure 1 45 shows him in action at frame 87 FBX 33 Figure 1 43 The Import Options window 5 Figure 1 44 The Animation Import Options section 34 CHAPTER 1 CHARACTER SKELETONS 5 Figure 1 45 Jack taking a swing To check your work so far you can compare it to boxing_v03 ma on the DVD For free and instant access motion capture the results are pretty good If you were to make extensive use of a motion capture library you could start with one of the skeletons provided by the library and build your character around it Summary Libraries are limiting At some point you ll need an animation they don t have or some type of transition between captures MotionBuilder by Autodesk is ideal for handling this type of work but it adds more to your pipeline In an ideal world you d have your own motion capture studio Keep reading and you ll get there
25. ould still be close enough It s difficult to state whether you should scale the character in its default pose or its first frame of animation If the first frame is a crouching or lying down position then you have to go with the default skeletal pose You don t want to go immediately to the default skeletal pose because it isn t a true representation of the actor it s rigid and unnatural If you have control over the motion capture session it s ideal to have the actor pose in the same position as your CG character to obtain a suitable default skeletal pose MOoTION CAPTURE 19 6 Select mocap_GRP and go to frame 13 Turn on Snap To Point Press D and snap 10 l1 12 13 the group s center to the root node of the motion capture skeleton With Snap To Point still on snap mocap_GRP to Jack s root_JNT The two skeletons are now collocated To get the skeletons to stay collocated you need to add a point constraint l Figure 1 22 Shift select root and root_JNT and choose Constrain gt Point Reset the settings and a ae Add an IK handle to choose Add root _JNT Orient constraints would be the logical choice 9 to align Jack s skeleton with the motion capture skeleton but the likelihood of the motion f an capture skeleton being oriented with your skel ey eton is slim to none The logical step is to apply Th the orient constraint and maintain its offset You 4 now have the tedious task of tr
26. ptions WEIGHTING CLAVICLE ROTATION In the final rig the clavicle will rotate only a little in the Z axis To achieve a proper shoulder shrug most of its motion will come from the joint s local X translation Rotations are being used here simply for convenience All the rotate values are at 0 0 making it easy to return the joint to its original position Otherwise you d keyframe the joint s translation to retain its original value Figure 1 10 5 The spine and left shoulder joints are the first to tackle The torso requires Getting these deformations along the spine correct makes the most extensive fixes it easier to add the appendages Select the skin and choose Skin gt Edit Smooth Skin gt Paint Skin Weights Tool 6 Knowing the target area to fix lets you customize the Paint Weights tool Ctrl select the following joints e root_JNT e spinel_JNT e spine2_JNT e clavicleLft_JNT e shoulderLft_JNT e elbowLft_JNT e radiusLft_JNT e collar JNT Choose the tack icon in the upper right corner of the Influences list The selected joints are now isolated 7 Open the Gradient section and select Use Color Map The weight maps go from black and white to color Select clavicleLft_JNT Toggle the check box for Use Color Map a few times and notice the difference in the display The information is identical for both but your eyes can t perceive the subtleties in the grayscale shading Figure 1 11 shows the differenc
27. s project You can try them on your own or continue to the next project Mirror and Copying Weights Symmetrical characters are great because you only have to build half of them You can mirror just about every aspect Skin weighting is no exception mirroring significantly reduces the amount of redundant work Perhaps an even greater tool than mirroring is the Copy Skin Weights tool It allows you to copy weights from one skin to another regardless of the skeleton It works on entire meshes as well as components Copy Skin Weights is very flexible and a time saver Project Mirror and Copy Weights Half of the character is weighted In the next project you ll mirror the weights and then clean them up In the latter half of the project you ll copy the single mesh weights over to the divided mesh with the head separated from the body Follow these steps ey 1 Open the jackWeights_v04 ma scene from the chapter1 scenes folder on the DVD The scene picks up where the previous project left off Half of the character is weighted 2 10 l1 WEIGHTING 15 Select Jack s geometry Choose Skin gt Edit Smooth Skin gt Mirror Skin Weights Use Figure 1 18 Figure 1 18 to set the mirror options Click Mirror to apply the settings Mirror Skin Weight options The Mirror Skin Weights tool is highly effective but _ EOE you can still have a few stray vertices Rotate shoul Edt Help derRght_JNT to 50 0 units in the Z A single ver
28. shoulders they look too high Your first thought might be to adjust the animation or offset the IK handle Both those solutions can cause major headaches Adjusting the IK handle only throws the timing off for the rest of the arm Adding keyframes over the top via a layer or secondary rig has the potential to do the same thing More impor tant doing so changes the performance Your goal is to use the data as is It s the performance you want Altering it even a little destroys the actor s intentions and worse the timing of the captured motion Maintaining its integ rity is paramount In the next project you ll address the shoulder issue without altering the performance Project Shoulder Fix In the previous project you relied solely on SC IK handles to drive Jack s skeleton They worked for 90 percent of the character However using them on Figure 1 29 Check the align ment at frame 550 the shoulders has forced the shoulders into a higher constrained position that isn t natural for Jack In this project you ll remove the handle and use only an orient constraint 1 Open the mocap_v05 ma scene from the chapter1 scenes folder on the DVD It s the same scene that Project Motion Test ended with 2 Go to frame 1 and look at the shoulders see Figure 1 30 3 Select ikHandle8 and delete it MOTION CAPTURE 25 4 Select clavicleLft_JNT Change all of its Rotation values to 0 0 Figure 1 30
29. t hierarchy that has been properly oriented Its construction is simple but its joint placement is meticulously arranged Joints in the human body aren t always centered within the skin s volume For instance the bones along the spine are pushed to the back of the torso with the ribcage protruding from the front On a CG character it s best to position the spine joints cen tered within the body doing so makes the deformations function more naturally The reason is that the human body is filled with bones organs and fluid all of which play a factor in motion A CG character is an empty volume and its anatomy is implied Figure 1 3 shows the CG character s spine placement Most often what works best when placing joints is old fashioned trial and error You can bind the joints to the skin and test their rotation Choosing Skin gt Edit Smooth Skin gt Move Skinned Joints Tool lets you make rapid changes to a joint s location The tool works great for determining the position of the hip and knee see Figure 1 4 CHARACTER PIPELINE Figure 1 3 Jack s spine is positioned almost centered in his body and is vertically aligned The arm joints are positioned in a similar fashion to the leg However their joints are located based on the shape of the character s skin You want to pay close atten tion to the angle of the fingers to ensure proper rotation Figure 1 5 shows the hand and the joint placement Performance Capture P
30. t_JNT Switch to wristLft_JNT and replace all the weights with 0 0 down to the wrist joint itself Figure 1 16 The elbow weights have been smoothed and cleaned up Select the Smooth Paint operation Toggle back and forth between the elbow and shoul der joints smoothing the weights until they re blended nicely When youre satisfied clean up the smaller weights by painting them with a 0 0 value The weights of the two joints should only bleed over the elbow area by a couple of edge loops Figure 1 16 shows the finished results The radius and wrist joints work together the radius rotates in the X while the wrist handles the Y and Z axes The radius weights are good except where they influence the wrist Follow the same procedures you used for the previous joints to remove the unnecessary weighting Rotate wristLft_JNT to 40 0 units in the Z After you smooth the weights around the wrist joint use the Scale Paint operation on both wristLft_JNT and radiusLft_JNT to reduce the weights and create a tight crease in the skin A Value of 0 9 works well Figure 1 17 shows how the wrist and the wristLft_JNT weight map should look 14 CHAPTER 1 CHARACTER SKELETONS Figure 1 17 Scale the weights to get a crease around the bent wrist ey To check your work so far you can compare it to jackWeights_v03 ma on the DVD 26 Do the hip leg and neck using the same procedure you ve followed for the other joints in thi
31. tex a A ms i Crechonm Positive to negative X ba x3 from the torso is attached to the upper arm see ae Figure 1 19 ee Tose component Influence Association 1 Cosest jant Stray vertices like these are easy fixes Select the ae Influence Association 2 Mone r problem vertex and choose Skin gt Edit Smooth Skin gt Normalize Weight Hammer In an instant the vertex is averaged with the surrounding vertices and deforms naturally A closer inspection reveals a second vertex just above the armpit Select it and use Weight Hammer to fix it Rotate the rest of the joints to make sure they all look good The weights are finished you can now transfer them to the separated head and body ey geometries Choose File gt Import and open the jackParts ma scene file from the chapterl1 scenes folder on the DVD The head and body nodes are now in the scene The two new Figure 1 19 One vertex under the arm didn t mir ror properly pieces are assigned to the layer named PARTS Turn off the visibility for the JACK_MESH layer Shift select root_JNT head and body Choose Skin gt Bind Skin gt Smooth Bind In the tool options set Skinning Method to Dual Quaternion Click Bind Skin Turn on the visibility for the JACK_MESH layer Shift select jack and body Using the default settings choose Skin gt Edit Smooth Skin gt Copy Skin Weights Shift select jack and head Choose Skin gt Ed
32. the scene it s significantly larger than Jack s skeleton and has captured motion of an exercise routine It s assigned to a layer called MOTION_CAPTURE 2 Open the Outliner and select the root node Group this to an empty group node by pressing Ctrl G Rename the group node mocap_GRP 3 Select mocap_GRP and scale it uniformly to the approximate size of Jack 0 03605 is good see Figure 1 21 Make a note of the scale you end up using it can be used for all the motion cap ture done with the same actor Later in the chapter you ll apply different motion from the same actor 4 Turn off the visibility on the body layer 5 The group node is mainly needed for scale You can also use it to offset the skeleton You want to match the root joint of the motion capture skeleton to Jack s skeleton Before you can do this you need to make sure youre at the default skeletal pose for both skeletons In the Outliner select the root node on the motion capture skeleton The timeline should fill up with red keyframes Change the start time to 100 Go to frame 100 and then click the Step Forward One Key button on the timeline con trols Doing so reveals that the first keyframe is at 13 Change the timeline to match the beginning and end 18 CHAPTER 1 CHARACTER SKELETONS Figure 1 21 Scale the motion capture group to match the size of Jack GROUP SCALE At this point you may want to reevaluate the character s scale It sh
33. tle down The geometry of the head is attached to the muscles The muscles drive the geometric skin using nCloth for both the muscles and face geometry This creates very complex defor mations It also makes it necessary to isolate the head from the rest of the body You use basic weighting to control every thing but the face Detaching the head from the body allows the head to be nCloth Ultimately the head is a hybrid of nCloth and traditional weighting The seam where the head and body connect is hidden by the character s clothes but it s nevertheless held together by the basic weighting It s also important to mention the mouth Having a char acter realistically express emotion and speak places a signifi cant emphasis on the teeth tongue and rest of the mouth Modeling these parts isn t as critical as modeling the exterior skin but it s essential that they exist Figure 1 2 shows the interior of Jack s mouth Base Skeleton Building the skeleton is more of a technical achievement than an artistic one The skele ton s functionality in the overall pipeline is primary You must name the joints and orient them properly You need to establish layers to toggle a joint s visibility as well as its selec tion status These things are important above all however is joint placement In the final setup the character has two skeletons a base skeleton and a motion capture skeleton The base skeleton is nothing more than a join
34. up node Use Ctrl G for the keyboard shortcut 3 In order for FBX to update a scene element the names must be the same for all the nodes you want to update Rename the group node to mocap_GRP exactly as you did with Project Motion Test 4 Scale the group node to 0 03605 match ing the scale of Jack again referencing the motion capture project you did earlier in the chapter This was the scale used in step 3 10 FBX 31 Select mocap_GRP and snap its pivot point to the root joint You can hold D and V on the keyboard to do both actions simultaneously This is a good time to save your scene To check your work so far you can compare it to boxing_v02 ma on the DVD Choose File gt Export All Change File Type to FBX Export and click Edit Preset see Figure 1 37 When you click Edit Preset the Edit Export Preset window pops up The FBX file format has numerous settings you can adjust You only need to concern yourself with the options related to animation We ll go through each section ignoring the ones that are irrelevant to this export Open the Animation section it has seven subsec tions Make sure Animation is selected Under Extra Options make sure Use Scene Name is unchecked You don t want to alter the name of anything in the scene doing so would prevent the identical nodes from being updated see Figure 1 38 Select Bake Animation The Start and End times should be filled
35. ying to align the Tees ieee iN ee ee cata RoR Ol J ee No en tO BR oe h l w x Si A ae ad De rs yo a Be Se A better solution is to use single chain SC IK Ve IA A TA aie handles You can snap the IK handle to the end of PEAN M A i the bone you need to align with Adding a point on afl ay constraint forces the handle to follow along An SNEL MLA added benefit of the SC handle is that you can EF AN also constrain its orientation allowing you to ig replicate a bone s twisting motion r 4 fp The best place to start is at the root Turn on f A Y Reference for the MOTION_CAPTURE layer l EF i Choose Skeleton gt IK Handle Tool Click Reset EX Tool at the top of the toolbar to return the set HEE ee tings to their defaults Current Solver is set to ikSCsolver In Perspective choose root_JNT and then spinel_ EE orient Constr ar JNT Figure 1 22 shows the results avila Maintain offset w Turn off Reference for the MOTION CAPTURE ott Animation Layer Mone layer and turn on Reference for the SKELETON layer Set layer to ovenide v Constraint axes w Al Shift select upperback and ikHandlel Choose Weight 1 0000 Constrain gt Point Reset the tool to use the defaults and click Add Select lowerback and ikHandlel and choose Figure 1 23 Orient constraint selected and use the settings from Figure 1 23 options Constrain gt Orient Make sure Maintain Offset is 20 CHAPTER 1 CHARACTER SKELET
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