Overall

A close up

CS 838 Animation Project 2 Prof. Gleicher   Min Zhong Jake Kretz April, 2000

Overview
This is a self-directed motion capture system. Many buttons have warning/help to guide the user through correct usage of the system. With the knowledge of different mouse
functions, one can learn to use the system without reading other parts of the user manual.
 

• References
• Features and Implementation discussion
• User Manual
• code and exe

• Quaternion
Referred to the paper "Quaternions" by Ken Shoemake.
• Exponential map
Referred to the paper "Parctical Parameterization of Rotaitons Using the Exponential Map" by F. Sebastian Grassia.
• Quaternion slerp
Referred to this site.
• Quaternion Spline interpolation
Implemented a rational berzier quaternion spline constructed in Eucleadian space and converted back to S3 space.  Algortithm developed by J.K. Johstone and J.P.Williams,
"A rational quaternion spline of arbitrary continuity", August, 1999.
• Berzier curve (for constructing quaternion spline)
Used the definition on P327 of text "Computer Graphics" by Hearn and Baker.
• Camera angle change in OMIN mode
Copied Gleicher's cs638 code.
• Camera movement in FOLLOW mode
With helpful advice from my friend Brian Ostergren.
• RunButton.cpp, .h
 Modified Gleicher's cs638 code.
• Debug.cpp, .h
Modified Jerome Heckenkamp's code from our cs640 project, originallly from his cs564 prof.

• Interpolation
• Euler Linear and Cardinal interpolation.
• Quaternion: Slerp, rational berzier spline

In the spline case, I didn't take measure against the "ill conditioning near the pole" case, this may attribute to the unstable behavior in some interpolations, e.g. the quaternion spines jumps wildly about the pole.  The authors point out (pg.14) that the mapping of the into Euclidean space is un stable if any of the data is close to the pole, or the angle formed by p (in S3) and (1,0,0,0) is less than 30 degrees.
• Exponential map:

Linear: straight forward interpolation of emap 3-vectors.
Slerp: quaternion slerp, then convert back to emap 3-vector.
Assumptions
Frames before the first key and after the last key and other non-interpolatable frames* are not interpolated.   They are copied from the original data.
* Non-interpolatable frames:
    For the case of Berzier (interpolates between every 4 keys), if (key count % 3 + 1 != 0, frames between some of the last 3 keys are not interpolatable).
    Cardinal (interpolates between middle two of every 4 keys), frames from the second to last key on are not interpolated.
• Camera
• Ominicient (attemp to be) mode

The inital look at point is set at the mid point between the motion's starting position(A) and end position(B).  The eye point is taken to be a point 1.5 |AB|, on AB's perpendicular bisecting line.  This obviously doesn't work well for looping motions with two ends close to each other.  So this mode is really only enabled when it's initially set to OMIN at file loading time.  When fine toning the camera in the FOLLOW and going back to this mode, it's really just changing to a fixed camera.
Zooming in and out in the mode is done by changing field of view.
• Follow mode

LookAt point is set to be the center of the motion.  Call L a vector from the LookAt to the Eye point.
There three user control knobs for adjusting the camera:
    Lag distance: how far the Eye lag behind LookAt, i.e. |L|.
    Theta: angle between L's xz plane projection and x-axis, the horizontal adjustment for Eye.
    Phi:    angle between L and xz plane, the vertical adjustment for Eye.
• Keyframing:

Automatic key every nth and manual keying options, with delete specific frame
and clear all frames options.  All keys are automatically clear upon loading a new motion file.
 
• Stage

2 optional lights, shadow, and optional floor.
 
•   Parser Assumptions:

      -It's a bvh parser
      -It assumes max of MAX_CHILDREN joints from a root
      -It assumes the following channel ordering:
          for 6 chan: (xt, yt, zt, zr, xr, yr);  for 3 chan: (zr, xr, yr).
 
• Discussion

   So how do different interpolation methods compare?
    Overall, in the rank of worst to best aprroximately,    Linear -> Euler Cubic -> QuatSplin * -> Slerp.
    *Note, QuatSpline seems to work better than any Euler for more dynamic motions (e.g. dance01.bvh), while Slerp seems to be the best formost other situations.  This is probably due to the fact that in the QuatSpline implementation, I did not take measure to avoid pole. According to the paper, this interpolation becomes unstable when the inverse mapped (S3->R4) quats are less than 30 degrees.

Usage

Mouse
    The two mouse buttons manuvers the camera movement.
    In OMIN mode
        CTRL+LMB: the horizontal dragging motion enables zoom in and out
        LMB:    dolly and rotates the world.
    FOLLOW mode
        CTRL+LMB:  the horizontal dragging motion enables zoom in and out
        LMB:    Horizontal dragging rotates the view horizontally.  The horizontal angle is restricted to 0-360, so drag the other direction when it stops responding to mouse movement.
        RMB:    Vertical dragging rotates the view vertically.  The vertical angle is restricted to 0-90, so drag the other direction when it stops responding to mouse movement.

Motion file loading
    upon loading a new .bvh, all keys and markers are cleared and interp and marker browsers are reset to default setting.

Display
    It is capable of displaying three rotations (Euler, quaternion, and exponential map) simultaneously for visual comparison.
    On each rotation interpolation type browser, choose "hide" to hide the motion from that rotation, "None" to show the non-interpolated motion for that rotation type, or
    others for appropriate interpolation type.

    Viewing range can be changed by specifying new "begin" and "end" frames.

Markers
-loading marker placement file
    Marker request files can be loaded using the "Load Marker Request" button any time during the animation. As new marker file is loaded, old markers are erased.
    Each invalid marker (non existing parent joint) is automatically ignored with a warning message displayed.
-display
    Markers are displayed for the choosen rotation on the "marker type" browser if that rotation is currently on display ("Hide" not selected).
    The last 20 frames of each marker trace are displayed.
-export
    Marker information exported is for the choosen interpolation type (rotation interpolation browser) of the choosen rotation type (Marker type browser).

Endsite markers
    Choose the endsite(s) want to be traced in the endsite browser, set "marker type" browser to the desired rotation type,
    and make sure that rotation type is not on "Hide" selection from its interpolation browser.
    This is an after-thought add-on after everything else is implemented.  So only one type of rotation trace is shown at a time.
    It would have been neat to be able to compare traces for differenct interpolation type.
    Endsite browser: hold down CTRL or SHIFT key to select multiple or toggle.

Keyframing
    Two modes are available: automatically key every nth frame or manually select each key frame.
    For complex motion, it is recommanded that key nth for a reasonable value of "nth", then customally key the missing important frames to achieve good effect.
        "Key this frame": first drag the slider to the desired key frame, and then click the button to key it.
        "Un-key" works similarly. It removes the key frame the time slide is pointing at.
        "Display keys" button displays all keys keyed so far on console.
        "Clear keys" clears all keys.

back to Overview.

Source Code and the end product

    proj2.exe    (585KB)
    proj2.dsp
    proj2.dsw
    some sample bvh motion data files in this directory

     proj2.h        has includes and some defines.
    main.cpp     pops up the UI, starts the even loop.
    debug.cpp, debug.h:    for debug prints.
    3DUtils.cpp:    callbacks and related.
    RunButton.cpp, RunButton.h:    Play button and slider related.
    viewer.cpp,  viewer.h:    Gl_Win class methods
    parser.cpp:    reads in the .bvh motion data and fills a MotionCapturer object.
    MotionCapturer.cpp, MotionCapturer.h:    defines the structure for parsed data, most related functions in parser.cpp.
    RotConverter.cpp, RotConverter.h:     converts between Euler, quaternion and exponential map representations.
    interpolater.cpp:    handles interpolation.
    quatSpline.cpp:    quaternion spline related.
    stage.cpp:    camera, lighting and shadow related.
    Marker.cpp  Marker.h:     marker trace related
    vector.cpp, vector.h:    3D and 4D vector manipulation library.

That's all folks! back to Overview.