A summary of my programming
assignment. The source file for the main animation is available: motion.c, as well as the executable
Part 1: Reading in Motion Capture Data
My program is capable of reading in specific files in .bvh
(Biovision Hierarchy) format, with certain restrictions: I assume that all
limbs are fixed length (or remain attached) (i.e. there are no
translational components), except for the root node, which is allowed to
translate. I also assume that all joints can make rotations, and that
these rotations are Euler angles, and in zxy order (which they were for
the 4 files I looked at the most). The bvh file should be given as a
command line argument.
I wrote several files that helped with this. They are:
- Bone.h and
Bone.c: The tree structure which stored all of
the joints read from the file. Fields included space for: the name of the
joint; which node we are looking at; the parent node; the child nodes;
the number of children; Vectors for rotations (root and non-ends) and
translations (for the root. This field stored end-effector locations
for ends); a pointer to a set of quaternions; the offset of this joint
from the one above it; how many frames there are, and how often those
frames should be displayed.
- Vector.h:A 3-d vector
- MCWString.h and
MCWString.c: Used to parse individual lines
from the file (a combination of the StringTokenizer and String class from
Java).
- BVH.h and
BVH.c: The driver to read a bvh file.
Part 2: Displaying the Data
My program used OpenGL do display the motion. I represented all of my
limbs as sticks, with orange boxes at the joints, and lavender spheres as
the end effectors. I made little effort to control the frame rate: using
certain parts of the program features seemed to eliminate the need for
this (at least on the cool Intel machines in 1351 and 1363). The user can
pause the animation by clicking the left button in the window. Once the
motion is paused, the user can then use the middle button to go back one
frame, and the right button to advance one frame.
The sequence always looks at (using gluLookAt()) the root node of the
image.
The user can choose to pan and tilt the camera around the figure (4 and 6
on the keypad to pan, 2 and 8 to tilt). The user can also zoom in by
hittng +, or zoom out by hitting -. The user may return to the
default view by hitting 5.
Part 3: Computing the Forward Kinematics
The program computes the forward kinematics of the end effectors. It does
this by using the transformation matrices provided by OpenGL, and caching
them. To view the end effectors, the user need hit t (for toggle end effectors, obviously). To stop
viewing end effectors, hit t again.
Part 4: Convert to Quaternions
There is an option to view all rotations as quaternions: the user needs to
hit q to begin this feature.
Part 5: Compare Interpolation
The user can also compare the view the motion using interpolation of
angles. The user must first specify a start frame by hitting s, and then an end frame by hitting e. To view the effects of interpolation, the user
should hit i. Interpolation done using slerps for
the quaternions, and linear interpolation for the Euler angles.
User interface summary
| Key | Effect |
| Camera
Control |
| 4 | Pan left |
| 6 | Pan right |
| 8 | Tilt up |
| 2 | Tilt down |
| 5 | Restore original view |
| + | Zoom in |
| - | Zoom out |
| Quaternions, end
effectors, and interpolation |
| q | Use Quaternions |
| s | Beginning frame for interpolation |
| e | Ending frame for interpolation |
| c | Clear beginning and end frames |
| t | Toggle viewing of end effectors |
| Frame
Advancement |
| Left Mouse | Pause (or restart) the animation |
| Middle Mouse | Rewind animation one frame |
| Right Mouse | Advance animation one frame |