Decompressing Quaternion Problem

IggyPop · 2012-07-10T18:27:29

Hi, I'm a little bit stuck with decompressing my Quaternions used in key frame animation. Angles that are close to 180 are some times negative when they should not and vise versa. Instead of -179.6 it should be 179.6 which causes a whole ~360 degree rotation when translating between say frame 5-10 since I drop certain frames. My compression code: [source lang="cpp"] if(q.w < 0) q.Flip(); // positive so i don't have to store sign double scale = sqrt( q.v.x * q.v.x + q.v.y * q.v.y + q.v.z * q.v.z + q.w * q.w); scale = (32767.0 / scale ) + 0.5; floor(q.v.x * scale); floor(q.v.y * scale); floor(q.v.z * scale); [/source] Which gives me 3 signed __int16 values. My Decompression code: [source lang="cpp"] static double scale = 32767.0 - 0.5; q.v.x /= scale; q.v.y /= scale; q.v.z /= scale; double temp = ( (q.v.x * q.v.x) + (q.v.y * q.v.y) + (q.v.z * q.v.z) ); if(temp > 1) { // wtf } q.w = sqrt(1 - temp); [/source] Also I sometimes get values of 'temp' that are > 1 which makes no sense (to me). So if anyone can spot the error that would be great, I'm still learning Results of my searching around before making a topic: I came across a post on here that seamed relevant but I'm unsure as to what extra checks are required. (Snip of post) There are a couple of issues with this. First you need an additional sign bit to distinguish between w being posive and negative, both of which are possible. You can avoid this though by checking the sign of w before compressing and if it's negative multiply the whole quaternion by -1, so w is always positive and you take the positive square root when decompressing. But this can cause problems for some data - e.g. by introducing jumps into a sequence of keyframes of an animation, requiring extra checks when interpolating them. [/quote] Original Topic: http://www.gamedev.n...ed-quaternions/ I've also read: Game Programming Gems 3: Section 2.4 on quaternion compression be to no avial. Thanks for your time.

Math and Physics Programming

Started by IggyPop July 05, 2012 02:34 AM

12 comments, last by IggyPop 11 years, 9 months ago

IggyPop

108

Author

July 07, 2012 02:06 PM

-179.9 and 180.1 are the same angle. So the angle isn't "incorrect" in any meaningful way. If the point is that it should be 179.9 and not 180.1, you need to make your code more robust.

Again, if you use quaternions during the interpolation, many problems will go away.

yes they are the same angle but Maya requires Euler angles. so the problem arises when maya translates between them.

The top is what I want but the bottom is what happens: (since it dose a whole 360 spin to get from negative 180 to postivie 180)

alvaro

21,604

July 07, 2012 02:31 PM

Can you tell Maya what the angles are at every frame, instead of letting it interpolate?

IggyPop

108

Author

July 09, 2012 07:23 AM

Can you tell Maya what the angles are at every frame, instead of letting it interpolate?

Yes I can Id need to generate the values myself tho.

I've been looking into the curve editor in Maya and wrote the basias of a c++ plugin for maya gonna have a play with that see what happens.

IggyPop

108

Author

July 10, 2012 06:27 PM

Ok After more and more time spent on google, I finaly stumble apon this:

http://download.autodesk.com/global/docs/maya2013/en_us/index.html?url=files/Keyframe_Animation_Set_rotation_interpolation_for_curves.htm,topicNumber=d30e220991

This now makes animation curves take the shortest route to the next angle, fixing the 359 degress of rotation, instead of the 1 degree intended.

Thanks for all your input alvaro

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