When the hand rotates upwards, it changes the orientations of ALL fingers attached to that hand.įor example if you’re calculing the angle from the tip bone of the index finger to the hand bone will change in a chain reaction when the hand bone rotates, even if the fingers don’t move. This was especially important for the hands and fingers. Using Dihedral AnglesĮven with all my efforts put into calculating the rotations and transferring it over, it worked with a simple one to one vector pair example the only thing I didn’t see coming was the fact that a rig has many joints linked and one change in the rotation of a parent bone will cause a chain reaction in all attached children bones. With this new knowledge, I started changing the way I calculate the offset angle and if you read on, you’ll see the little by little progress I make along my journey. This is more of a Houdini thing and I believe every 3D application software will have its own way of storing and manipulating this data. I also needed to use the Rig Attribute Wrangle to update the localtransform attributes stored within each joint of the KineFX rig in Houdini. You have to figure out the delta rotation and the find out the axis of the rotation, which really means where to rotate and how much to rotate. Well to the least the local transformations no longer made sense when I forcefully overwrite the positions to match the mocap. I was simply overwriting the final position of the end of the bone, which sort of destroyed the local transformations. In the above attempts to transfer the delta rotation angles, my local transformations are not moving at all! This means I am NOT rotating the joints. The white balls represent the joints of the rig and the RGB colored hats represent the local axis of each joint. Notice the little red, green and blue hats on the white balls. Other 3D software probably has their own way of maintaining the local rotation data for each joint. This is where I realized the importance of using the local transformation matrix that comes with every KineFX skeleton in Houdini.
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