CGTalk - BVH/Skeleton Scaling Question?

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tvining

06-22-2008, 08:01 PM

I'm creating BVH files using the NaturalPoint Arena system to be used in Cinema 4D via the InterposerPro plugin for Poser. The motions I create in the Arena software look pretty good in the Arena editor, but when I export to BVH and import the BVH into Poser or C4D it looks jittery in places. The guys at NaturalPoint suggested that it might be a problem with improper scaling of the BVH to the Poser skeleton.

So I guess my question is: does BVH have a native "size" associated with it? I notice in the Arena software there is the option to scale the BVH upon export, but what does that really mean? And if there is a native size to the BVH or Poser skeleton, is there any way to find out what that is? And is there more to it than just size? Is it a question of proportion as well?

Also, one more question: is there any utility out there that might help me better scale the BVH file to a specific skeleton (like the Poser skeleton)?

A lot of questions--sorry--but I'm really scratching my head over this stuff!

Thanks--Tim

S-S

06-25-2008, 12:14 AM

I don't think there's anykind of additional "size" option in this sense in BVH, as it's just basicly a description of hierarchy, starting with "HIERARCHY" with joint locations and axis order.

This part of biovision file creates the hierarchy of your skeleton.

Then "MOTION" part contains rotations for each joint of skeleton, in every frame of animation, if there is animation.

I think you should just check the BVH file with text editor, see:

ROOT Hips
{
OFFSET 0.0000 0.0000 0.0000
CHANNELS 6 Xposition Yposition Zposition Zrotation Xrotation Yrotation
JOINT Chest
{
OFFSET 0.0415 6.2451 0.0203
CHANNELS 3 Zrotation Xrotation Yrotation
JOINT Chest2
{
OFFSET 0.0118 22.5192 -0.7792
CHANNELS 3 Zrotation Xrotation Yrotation
JOINT LeftCollar
{

... what kind of OFFSET values you have. These are just positions in space for joints. Then it's just a matter of finding out, how big distance this is in your 3d package? What size is your "typical" rig in your package? It might be that it's not suitable fo your needs. Then it would be nice to have some sort of "scaling" option for import. But you might be able to do it afterwards with your software.

In my file for example "ROOT" is located at 0,0,0 in setup frame and "CHEST" at 0.04 6.24 0.02.

I've myself written a simple BVH importer, which also has "scaling" option. This makes it possible to use BVH data in different scale scenes. This was for 3ds Max.

Hope this helps!

tvining

06-25-2008, 12:59 AM

Thanks! I think that points me in the right direction. I'll take a look into my BVH files and see if I can learn anything from them.

Thanks again--Tim

eek

06-26-2008, 11:08 PM

OFFSET is just a direction, it can be used as a length in theory, its the offset position from it parent.

With scaling you would just multiply this value, by a variable.

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