Plotting Optical Data to a Prop

#1

Hi Gang,

Is anybody familiar with the process if applying data from optical markers (c3d) to a character holding a prop?

I have a model set up where he is holding an object in one hand. We recorded the mocap of a real actor holding a prop (both actor and prop were dressed with optical markers).
But when I define my markerset in motionbuilder, there is no place to assign the extra nodes of the prop markers.
I’ve been digging around the net but haven’t been able to find any concrete info on this. It seems like it should be a widely utilised feature in motionbuilder but no documentation anywhere.
The closest I’ve found was a pdf that states:
[left] [/left]
[left]2. Extract the props animation from the source markers to the target object using the appropriate constraints.[/left]
[left] [/left]
[left][size=2]That one line is the instruction for getting the motion onto a prop.[/size][/left]
[left][size=2]Can anyone shed light onto this? What constraints do I use? Rigid Body?[/size][/left]
[left]My character model is much smaller that the MB actor and c3d markers. If I use contstraints, do I need to scale my model up so that the optical markers for the prop are proportional to the prop model?[/left]
[left][size=2]I am using MotionBuilder 6.0 Pro and the mocap data is c3d.[/size][/left]
[left][size=2][/size] [/left]
[left][size=2]Currently, I have the object parent constrained to the models hand but I want to use the optical data from the mocap session.[/size][/left]
[left][size=2]The optical data for the character works fine. I am just stuck on how to apply the prop animation.[/size][/left]
[left][size=2][/size] [/left]
[left][size=2]Thanks for any help and advice,[/size][/left]
[left][size=2][/size] [/left]
[left][size=2]Art[/left]
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#2

A little update.

With the Help of Brian Windsor, I was able to get the motion from the optical data onto my prop using a 3 Point constraint and Rotation constraints. I simply used a Parent/Child constraint to attach the prop to the character’s hand.
The 3 Point constraint linked rotational data from 3 of my 5 markers to a null object. The null object then passed on the rotational values to my prop joint using the rotation constraint. I did it this way beacuse my model was much smaller than the actor and I used the null to zero out the rotations in world space.

Art

#3

you can get a similar effect with a rigid body constraint.

#4

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