extract SOP animation to object level

[Dries]

Hello all.

The exact project I'm working on is this: a piece of fruit is animated through Realflow as an RBD. I can export the animation to an SD file. The only way to import it in houdini as far as I know is throug Mark Story's SD import plugin which is a SOP. Every frame the object has a different rotation and position. What I want is to bake out position and rotation in world coordinates, so I can apply those transformations at object level, rather than SOP level to any object I want: a keyframe for every frame. This would make the channels exportable to Maya where it need to be rendered. (well, it really needs to, can't help it ;-))

Basically Maya expects a transformation matrix for every frame in world coordinates, which you only get in Houdini when using object level transformations and thus not when your animation is at SOP level. So can I extract SOP level animation (remember this is a non deforming object) in world coordinates?

Actually I can do what I'm asking here with translation, but how do I work out rotation? There is probably several ways. I might need to do this often in the future. So what's best?

I know I posted this on the sidefx forum as well, just trying to find out which would work best for me. If you forgive me for once.

DRie.s

[FrankFirsching]

Hello Dries!

Here is a scene for you, that might solve your problem. I don't know Mark's realflow plugins, so I have emulated this by animating a simple polysphere in SOPs on my own. The VEX-operator inside the scene is calculating the appropriate object level animation parameters, that can easily be referenced using a point(...) expression. The whole stuff is a bit tricky, because I encode the transformation parameters within the coordinates of 3 points. the first one stores the translation vector, the second one the rotation angles and the third one the scale factors. Additionally I needed to move the local origin of the shape to lie on a specific point on the mesh. The file has included some comments on each node.

hth

Frank

rigidXForm.hipnc.gz

[edward]

Hey Frank, I haven't opened up your file but did you see Jeff Willette's (sp) post on the SESI forum? He suggested using the Rivet OBJ which might also work.

[Dries]

Yes Jeff's Rivet thing works, but then if I want to do it accurately I have to construct an exact triangle in the geometry, which is doable but almost comes down to Frank's VEX solution. I'm busy on several jobs but I want to pin this one down. I'm close to a final hda which I'll post on the exchange website together with the export to maya script. Thanks to both.

Dries.

[edward]

Perhaps I'm asking a naive question but doesn't realflow export to maya directly?

[Dries]

It does, but I wanted to do some SOP level hocky pockery stuff in Houdini of which I have no idea how to do in Maya. Not that I would totally deny Maya potential maybe, but I just prefer Houdini so much more. It's just what I know best, I know, but still, it's a damn lovely piece of software. And on top of that, having this asset makes the method of exporting houdini animation to Maya a straightforward thing, as Maya doesn't generally use vertex transformations for non deforming objects.

D.