Simple Tracking of 3D RigidBodies in FluidsHarper Langston

MotivationAbility to track objects moving in fluids may provide insight into properties of the fluidVerify numerical simulationsStudy aquatic dynamics (current work in Math Department for example)Create nice animations, recreate scene with moving camera in 3D, etc.

Simple SetupTwo cameras with sloppy calibration (front view/side view)One cheap fish tank bought at PetcoMulti-colored balls, sliced open to allow desirable amount of water in and a cardboard ramp

First ExperimentsTrack a single ball, using Lucas-Kanade tracker and see how it looksPretty good as can be seen from video (slowed down 10 times on bottom good way of faking higher viscosity or heavier object)

Getting More ComplicatedWith the single ball, there was very little movement in the x-direction of camera #2, or in the global z-direction. Once we add the ramp, it gets more complicatedSloppy calibration: Use 1-in marks on side of fish tank as well as knowledge of camera location and size of tank. Further, measure radii of spheres in both camera views to find a scale factor. Choose camera #1 as true values, and scale camera #2s measurements accordingly.

Multiple Objects ContinuedSimply using Lucas-Kanade doesnt cut it. It would be good to use Condensation, but lets see if we can get away without it.To distinguish colored items, use Skin-Color Tracker, computing HSV to isolate the layer for each color.

ContinuingNow, it is easier to use Lucas-Kanade iteratively to track each object. Of course there is some degradation and noise, so use a Kalman filter to clean it up! May takes time for each motion to find right parameters but is smooth.

Lets put it togetherFirst, view the animation I captured from the front

ResultWith Skin-Color Tracker, Lucas-Kanade and Kalman Filter (Without purple ball)

How the Animation is ProducedTreat each ball as a single-jointed object and create a biovision format file (http://www.cs.wisc.edu/graphics/Courses/cs-838-1999/Jeff/BVH.html)Allows us to consider extensions to multi-jointed dynamic setups possiblyThe Bvh file is imported into Maya using Mayas MEL scripting language to create key frames for the skeletonPhysical geometric object is created in Maya and bound to the one-jointed skeletonWater effects and lighting, etc.!

Continuing OnSpent time working on adding Lucas Kanade with rotations [Bergen et al. 1992, Three-Frame Algorithm for Estimating Two-Component Image Motion]. Like we discussed in class, this allows us to find any affine transformation

Is Lucas-Kanade with Rotations, Scaling and Shearing Worth ItClearly, the last animation had many obstructions. Putting aside the clear need for a less crude setup, the Condensation algorithm would be a better choice for scenes cluttered with potentially many particlesExtension could also include [Koller-Meier, Ade, Tracking Multiple Objects Using the Condensation Algorithm]

collaborators Jarek Rossignac and Andrzej Szymczakpostdoc at GVU Center dealing with 3D surface and volume meshestriangle meshes in Pixars A Bugs Life