Euler Filter Algorithm?

[mcomet]

Hello,

I was wondering if anyone knew of or could point me in the right direction for what Maya 4's "Euler Filter" function does in the graph editor.

This is the routine that kind of "fixes" bad euler interpolation by moving curves + or - by 180 or 360 and stuff.... I'm curious to know how/why it works etc...

Thanks!

-comet

[ricgreen]

I am currently using this script to fix constrained rotations. Since the constrained rotations cant go higher than 360deg or lower than 0deg, the rotation skips back to 0 after 360 and to 360 after 0. This unfortunately creates sudden breaks in the baked anim curves. I think that this script looks for the sudden breaks and moves the keys between the breaks to the correct position.

[mcomet]

But it's doing stuff much more than that. For example you CAN create keys over 360 with Euler Filter..and if needed it will "raise" later keys up.

I agree it is fixing "breaks" or technical "discontinuities" but I can't seem to figure out how. Simply making a curve 180 or 181 doesn't neccesarily mean it will do anything. It seems to be related to the other 2 curves as well...ie: it requires XY & Z to work not just one.

If anyone knows of any articles/papers or where in graphics gems etc I might find info on this, I'd appreciate it!

-comet

[scotta]

I don't really understand the math involved, but I sort of know what is happening. For each keyframe, it checks for jumps of more than 90 degrees in both X and Z from the previous keyframe. When it finds this, it adds (or subracts) 180 from each of the X, Y, and Z keys and multiplies the Y value by -1. Then it adds (or subracts) 360 to any values that still have large jumps from the previous keyframe. I actually had this scripted before I knew how to use Euler Filter. There is probably more going on with the filter, but the transformation I described always seems to work just as well.

[mcomet]

Cool thanks scotta! I will give that a try. Sounds like it will work correctly.

So does this very very broad pseudoCode look right then?
note "diff" stuff is assumed to be "abs"olute already.

if (diffx > 90 AND diffz > 90) then
{
+/- X by 180
+/- Y by 180
+/- Z by 180
y * = -1;
}
if (diffX > 360) then
+/- X 360
if (diffY > 360) then
+/- Y 360
if (diffZ > 360) then
+/- Z 360