In January 2009 I had to give a presentation about Motion Retargeting, which I want to share with you now. I created it due to me attending a seminar about the latest developments in Computer Graphics at university and my presentation was about the Siggraph ’08 paper “Real-time Motion Retargeting to Highly Varied User-Created Morphologies” from Chris Hecker et al. You can check it out on Chris Hecker’s homepage - his website also contains a bunch of other really cool articles and presentations from various conferences, so it certainly is worth taking a look at it.
I’ve also sifted through quite a lot of IK papers and lectures for my presentation to understand the later part about the IK solver and the gait system in Spore and I’ve found a few links that are a nice read:
Chris Hecker’s talk about IK is a nice introduction (you can also download an audio stream, too).
Chris Welman’s Master Thesis is nice for reading about some of the common methods to solve IK problems.
Steve Rotenberg’s Computer Animation course is awesome - the slides about IK are nice, but the ones about locomotion are just awesome[[:they really really are!]]!
Particle IK and particle physics in games are related a lot (the constraint solver is pretty much the same) and for a nice read I can recommend Thomas Jakobsen’s Advanced Character Physics.
Pixar’s Physically Based Modelling course from 2001 is also nice to get going with physics again - it also explains everything you need to understand the idea behind ODE solvers in rigid body simulations and also has a very nice explanation of stiffness in ODEs.
Principles of Animal Locomotion is a very neat book that is about, well, the principles of animal locomotion, which I have read a bit thanks to Google books and it certainly is quite interesting.
Numerical Robot Kinematics Based on Stochastic and Molecular Simulation Methods is interesting, too, just to see what’s possible with particle IK.
Ive created a huge PowerPoint presentation for my seminar :-) It includes a few videos (thanks again to Chris Hecker for uploading them and replying to my emails incredibly quickly 1) and two awesome IK solvers that I’ve implemented with VBA macros 2 to show how CCD and Particle IK solvers work.
You can find a zip with all the videos and high resolution images here(includes both a PPT 2003 file and a 2007 file). I’ve also uploaded a small version without videos, macros as PPT 2003 file here, if you don’t feel like downloading the 23 MB .zip file.
Here’s a YouTube vimeo video of the two IK solvers:
The CCD solver usually works by solving one bone per inner iteration - I only added a max delta angle to create smooth animations to show how it works (same for the max delta length in the Particle IK solver).
It seems as if the CCD solver could converge faster if it randomly chose the first joint instead of starting with the end effector joint in every outer iteration.
I’ve exported the code into an additional IK Playground presentation which contains just one slide and the two IK solvers with the setup you see in the video above. You can find the PPT 2003 version of it here and the 2007 one here.
I’ve zipped up the macros here if you want to use them in your own slides. I’ve also written a handy VBA form that allows one to edit everything more easily (the macros are hardly documented though, but if anyone really wants to use them and runs into problems - you can always drop me a line or two in a comment :))
