This ASSIGNMENT is in two parts. Part 1 due 10/7 (before class) and Part 2 due 10/14 (before class).  Be warned the 1 week difference in due dates for part 1 and part 2 does not mean that part 2 is expected to only take 1 week. Work on part 2 before part 1 is due to make the DUE date.

Part 1: Motion blending and warping, due 10/7 (before class)

Motivation:

When an animator wants to create an animation using motion capture, rarely is the entire sequence captured in full. It is much more practical to gather a variety of short clips and blend them together in sequence. The ability to merge clips together allows clips to be reused which reduces time and resources spent during the often laborious motion capture process.

In this part of the assignment, you will blend and warp motion clips together. For example, if you have a walking clip and a running clip, can you interpolate the end of the walk with the beginning of the run in order to create a smooth transition from a walking clip to a running clip?

Background material:

• Witkin , Popovic, Motion warping, SIGGRAPH 1995 [ACM|PDF]

• Bodenheimer, B., Rose, C., Rosenthal, S., and Pella, J., "The Process of Motion Capture: Dealing with the Data'', Computer Animation and Simulation '97, Eurographics Animation Workshop, Sept. 1997, D. Thalmann and M. van de Panne, eds., Springer-Verlag, Wien, pp. 3-18. [PDF|PS|Bodenheimer's Web Page]

• Arikan and Forsyth, "Interactive Motion Generation From Examples", ACM Transactions on Graphics (TOG) , Proceedings of the 29th annual conference on Computer graphics and interactive techniques, 21(3), (SIGGRAPH 2002) July 2002 [PDF]

• Rose, C., Cohen, M., and Bodenheimer, B., ``Verbs and Adverbs: Multidimensional Motion Interpolation'', IEEE Computer Graphics and Applications, v. 18, no. 5, Sept. 1998, pp. 32-40. [PDF|PS|Bodenheimer's Web Page]

• Kovar , Gleicher , Pighin, "Motion Graphs" ACM Transactions on Graphics (TOG) , Proceedings of the 29th annual conference on Computer graphics and interactive techniques, 21(3), (SIGGRAPH 2002) July 2002 [PDF]

In particular, pay attention to the last two on how they do their transition selection. String together several clips of data and see if you can smoothly blend between them.

What you need to do:

You will need to choose a variety of clips of motion from

/net/dvfx/CA/Data/Mocap/ (in directory BVH)

(see http://www.cs.wisc.edu/graphics/Courses/cs-838-1999/Jeff/BVH.html
OR http://www.biomechanics-inc.com/software/data/bvh/index.html OR http://www.okino.com/conv/imp_bvh.htm for info on BVH format OR Working with Motion Capture File Formats)

(See other sources of data below)

More data is available from MoreBVH/directory from the above directory.

Combine data from these file to make longer sequences.

For this part of the problem set, You will write code to read in two or more .bvh clips and output a .bvh clip of the merged data. You may manually specify some parameters to guide your merging if necessary. The emphasis will be on your blending and warping algorithm -- that is, on the form of interpolation and other techniques you apply.

You must combine at least 2 sets of 2 motions together. That is, you will create 2 sequences, each of which is comprised of 2 merged clips.

In order to choose your clips and gather information to inform your algorithm, you will obviously need to look at the data.

Viewing MoCap DATA (and your results)

There are many options to view MoCap files.

1) Using MAYA

To view the data simply run Maya.

• Open the script editor
  Window | General Editors | Script Editor

• and do a
  File | Open Script

• and point it to the
  bvhimport.mel script. (in /net/dvfx/CA/Data/Mocap/MEL/)

• Once the script is loaded into the window, press Ctrl+Enter  to execute the script.

• It will open up a window, and you should point it to some mocap data.

To ensure smooth playback,

• go to
  Window | Settings/Preferences | Preferences.

• Click the Settings Category on the left-hand side and make sure that Time is set to NTSC (60 fps).

• Click on the Timeline category and make sure that Playback Speed is set to Half (15 fps).

• NOTE: These settings are for data captured at 120Hz (15fps/60fps = 1/4 sampling). Motion Capture can also come at 250Hz or other rates.

Let's take a look at some motion data. Click on a particular joint and periodically hit stop and start. Notice how the joint angles (the rotation values for the joint) change over time. Also note how the translation  values do NOT change. In order to define a pose for a 3D character at time t, we only need to specify the translation for the root joint (in this case, the hips), and traverse down the skeletal hierarchy, adjusting joint angles. (Note that if you wanted to write a retargeter, this would be useful to observe. This is mainly here for your own knowledge and experience.)

If you read through the BVH file you will actually see the BVH hierarchy defined in the first half of the file. The second half describes the joint angle data. For more information on the BVH format please see http://www.cs.wisc.edu/graphics/Courses/cs-838-1999/Jeff/BVH.html OR USC ICT's Motion Capture File Format Documentation OR Working with Motion Capture File Formats)

2) Some other viewer

If you can get a handle on the various MoCAP file formats (see Working with Motion Capture File Formats, OR USC ICT's Motion Capture File Format Documentation) then you can devise a simple viewer or also find one on the web that may help with viewing.  We have one of our own.  As with all free viewers, they are NOT perfect. See the following links for some examples (Not in order and with NO gurantees!)

• http://www.cse.ohio-state.edu/~parent/classes/888/Mocap/ (See  BVH utilities (Section 1) and the  Java Viewer at the bottom.)

• http://accad.osu.edu/~bwatkins/

• http://acabar.cafwap.net/~zier/anim/

• http://www.upl.cs.wisc.edu/~aselle/moview/

• http://bioviewer.sourceforge.net/index.html

• http://www.metamotion.com/mocap/BVH-player.zip

• http://mrl.nyu.edu/~hertzman/mosey/manual.html

• http://graphics.cs.cmu.edu/software/asfamcview.exe

IMPORTANT NOTE

When viewing the data, pay attention to aspects of the motion that might influence your ability to blend clips together. You will probably need to record some numbers (e.g. frame numbers) for your program to use when merging the clips. Better yet, implement a general algorithm for aligning, warping, and interpolating clips.

What to turn in:

You will need to turn in the .bvh files containing the merged clips as well as a write-up describing your approach. You will be graded on how smooth and natural the transitions look as well as the variety of the animations merged.

Submit in /net/dvfx/CA/2004/Submit/P2/<username>/
(Include a README.txt file to say which files are which)

Part 2: Skinning a character and interaction, due 10/14 (before class)

(A) In the directory /net/dvfx/CA/Data/Models/ is a 3D model of a stick figure, our beloved Woody (woody.mb). Load your clip into Maya and see if you can animate Woody with your mocap data. You will need to scale Woody to fit your skeleton and you will need to put him into the initial pose of your mocap data. Finally, you will need to skin the model to the skeleton in order for the model to be driven by the skeleton. See the Maya tutorial on Character Setup for more information. For your convenience, we have provided a tutorial showing a quick and dirty way to skin a character for this assignment.

Now that you know the basics, create a character using maya or find a character on the web and skin it. Your character must have different dimensions from Woody.

Using your new character, create animations for all your clips from part 1 -- that is, the input clips as well as the output clips.

(B) Try adding some object(s) into the scene and figuring out how to make your character interact with them. For example, put a ball in the way and have your character kick it or simply build a wall and have your character run through it. Yes, this means dynamics. But if you're clever, it may not be as difficult as you think.

What to turn in:

You will need to turn in videos (mpg/mov/avi) corresponding to each of your clips. Also turn in a short write-up discussing what you learned and observed from the character setup and animation. In particular, you may notice some peculiarities in the animation quality when your character is of quite different scale or shape from the original mocap skeleton.

Submit in /net/dvfx/CA/2004/Submit/PS2/<username>
(same directory as part 1).
(Include a README2.txt file to say which files are which)

HINTS: I'M LOST! WHERE DO I START?

Code:

Startup code (Windows-based) is located in the ProblemSets/PS2/code directory. Included are the header files and a .lib file (for Visual C++).

Start a Visual C++ Project and include the headers and library file in your project.

The code is what you will need to get started, and does reading and writing of BVH data. For example, you can do something like:

int main( int argc, char *argv[] )
{
    BVH myBVH;
    // read in command line argument as bvh file
    myBVH.read( argv[1] );
   
    // munge some data
   
    myBVH.write( "somefile.bvh" );
}

The data is stored in a structure called (of all things) "data", while the joint names and offsets are stored in an array. Look through the provided .H files for details. To access the joint angle data, you would do something like

    myBVH.data[frame#].body_parts[bodypart#].data[0] = 23.56;

note that the ending data element is an array of size 3 holding the XYZ values, e.g., data[0] = X, data[1] = Y, data[2] = Z. Again, read through the .H files for more information.

Motion blending:

How do you start blending data? Well, read through the papers mentioned above and you should get an idea of the naive approach. Essentially, the naive approach will find similarities towards the end of clip 1 and the beginning of clip 2 and do a smooth linear interpolation between the two. Naturally, a linear interpolation isn't the best way to do it - can you think of other ways? Cubic splines, perhaps?

Other Sources of MoCap Data

• http://mocap.cs.cmu.edu/

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