View Full Version : Volume Preservation with Biped Guide

01 January 2007, 10:10 PM
I'm new to XSI coming from Maya and I don't quite understand the volume controls that come with the biped rig. It looks as if the nulls that are made are part of the enveloping group and therefore will control the mesh, but how do I use the volume spheres that are created? One of the other things that happens is that the null that is created at the back of the thigh that I assume is meant to control the skinning at the butt jumps up to the front of the thigh when I move the foot control up too high. I try to read through the docs, but it didn't give me a whole lot. XSI looks to be the animation godsend from what I've been able to do with it thus far, and all these attributes look as if they will take my skinning to another level if I can only figure them out. Any help or direction will be much appreciated!

01 January 2007, 10:49 PM
The Volume spheres are implicit objects and the nulls use these objects as Constraints. ie the nulls cannot enter the sphere.
If you select a null and click on the constraint property (in kinematics) you will see 'bounding volume contstraint' applied
The purpose is to aid deformation in areas such as the back of the leg around the knee to stop intersecting to some degree and add the effect of the calf muscle squashing the thigh.

just out of interest, these constraints can be reversed. you can have a null stay inside a bounding volume.

01 January 2007, 12:45 AM
Okay, that makes sense as what I see happening. The question is how do I go about making the volume sphere the size I want? I've played around with the volume controls in the guide and I can't seem to find what makes which go where. For example; on the back of the lef leg there are primarily two splines and one in the front; the rear, the knee and the hip. It seems as if the placement for the nulls is based off of the center of the spline, which cannot be moved by itself. The spheres then are based off of the endpoints of the splines. I've tried adjusting the back of the knee spline; ie., LThighBack1 & 2, to go from the back of the knee to mid thigh, so that my nulls are placed in those specific points. Then I placed my rear spline; ie., LRear1 & 2, to go from the back of the hips to the bottom of the rear so the null is placed mid rear to control the rotation and volume of the buttocks. The my hip spline; ie., LHipTop & Bottom, along the outside of the hip so the the null would be placed there control the collapsing volume of the hip as the leg raises up. This is what I get

01 January 2007, 12:51 AM
I guess the bottom line I'm searching for is what controls the size of the volume sphere and the nulls.

01 January 2007, 01:42 AM
Well, I played around eniugh to get the volume sphere in a position that looks good, but I am still getting the null roll when I move the leg too far up.

Aside from this problem how do I use the volume sphere to control the volume of the model.

Just FYI I am simply using the default man model to try to keep everything at the defaults to learn from.

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01 January 2007, 01:42 AM
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