Motion Builder Gap Filling Methods:
1. The default gap filling is set to “rigid body.”
The program interpolates where the marker should be in space based on the position
of the other markers in the rigid body. This can be way off, if you have more
than one marker disappearing at the same time within a rigid body. This happened
to me quite often. There were a lot of gaps at the elbows, knees, wrists, and
ankles of my dogs.
View
an example of the Left Side Elbow marker in the floor when set to fill based
on rigid body.
View the marker
at the correct position.
2. For long gaps, set the curve to "Auto-linear", which flattens out
the animation curve so that you can set “Gap Key Frames” within
it to position the marker based on human visual approximation.
3. Alternately, you can set it to “Control Curve” and set “Gap
Key Frames” along the curve, but if you don’t flatten the curve
first, using "Auto-linear", you get another curve (the one you are
setting keyframes on) over the top of the original curve. This sometimes works
to control the curve underneath. However, if you decide you don’t like
one of your key frames and delete it, your underlying curve does not
go back to its original shape. Thus, the marker data becomes way off. I learned
this the hard way.
View an example
of a control curve on top of the underlying mocap data curve. The control
curve is the white line over the top of the yellow line.
4. You can use “Sample Curve” to be able to adjust the individual
keyframes set during the motion capture. This is very tedious and time consuming,
but sometimes very effective. I had 4 keyframe squares between each “frame”
of the animation in Motion Builder. There are many keyframes set for each second
of data. I captured the data at 120 Hz. I believe this means 120 frames per
second.
View
an example of one keyframe being moved on a "Sample Curve" setting.
Note, the program ran slow with Cam Studio recording the screen at the same
time, so there is lag in the marker movement after the key frame is moved. Once
you move one key frame, you have to move the others to form a smooth curve,
or you end up with a peak or spike in the marker movement.
5. Auto-Bezier is another gap filling method that works well over short
gaps on curves that are slow changing and smooth. This filter basically smooths
out the curve within the gap.
Again, filling gaps, just like cleaning done in Workstation, involves
selecting one or two markers at a time, playing back the animation very slow,
or even frame by frame, both on a lateral view of the dog, and either an overhead
or frontal view. By checking the marker in different views, you can catch any
peaks or spikes or wobbles that occur on a different axis than the one in the
previous view. It’s all very tedious, time consuming work. It is almost
a black hole of time. I wasn’t able to finish filling all gaps in every
take for every dog. I have two dogs’ takes completely done and ready for
import into Maya at this time. One is a healthy dog (Stevie), and the other
is a hip dysplastic dog (Maddy). I’m going to complete a cranial cruciate
ligament rupture next. This way, I’ll at least have one dog of each condition
cleaned by January.
Altogether, I motion captured 2 normal gait, 2 hip dysplastic dogs, and 2 cranial
cruciate ligament ruptures. The dogs that aren’t completely done in Motion
Builder have their rigid bodies created and they are converted to .fbx format
– a start. A couple have human actors mapped to the marker data –
which I learned was a waste of time.
View the normal dog’s cleaned marker data
(Stevie).
View the hip dysplastic dog’s cleaned marker
data (Maddy).