Hi,

I've cached out a low-res fractured geometry and was wondering is there any way I could read it back into houdini with a file sop and use it as a transform for my hi-res geometries?
Basically I just wanted to avoid doing my sim with hi-res geos to save time. I've tried using dopimport with “transform input geometry” but that doesn't seem to save much time for me.

As long as you have an equal number of pieces in the hi rez what iv always done is sim using the low res. Then use a dop import bringing in that low res' sim set to transform input on the hi rez geo and cache that out. Hope that makes sense, if not il make an example file


Edit: oh didnt realize this was your post boon ahaha

Hey, this sounds like a pretty nice idea. An example file would be great if that's possible?

there is an example of how to do this in the docs. http://www.sidefx.com/docs/houdini12.1/nodes/sop/dopimport [sidefx.com]

Ah great. Thanks, will take a look …

Or you can apply the transforms directly to the pieces. (Same thing happens when doing delayed load instancing). You need two things for this:
A) the pieces geometry (initial state of pieces) with a “piece” attribute (can be turned on to be kept from the voronoi sop - or create your own with the connectivity sop)
B) the points from the sim, coming from the dopimport (as points to represent objects)

1) Bring in the points with the dopimport. (-> B)
2) Attribprmote a “piece” attribute on your pieces geometry to points. (-> A)
3) use this piece attribute as a lookup in a vopsop to apply the orient, P and scale attributes coming from the dopimport (this gives you really fast transforms, much faster than the copy sop). (A to look up in B)

Now here is the cool bit: You can replace the pieces geometry (A) with whatever geo you want (C), as long as you make sure the piece attribute is transferred, because eventually that is what is used to look up the transformation attributes (in B). (C to look up in B, using the piece attribute from A).

The C geometry can be clusters of other geometry, as long as they all have the same “piece attribute” they will look up the same transformation from the points (B). This is useful to simulate with lower resolution convex geometry, but then create high resolution clusters of pieces.


In order for this to work, you need to learn how you can recreate the transformation behaviour the copy sop does. Use vops ( learn to apply orient, P and scale to build the transform that is then applied to the points), as it is the fastest way.
-> the main thing is to extract the rotations out of the orient quaternion. I generally go import(orient) -> quaternion to matrix3 -> matrix 3 to matrix 4 -> extract rotations -> build transform (also plug the P and scale into this).

Hope this makes sense.

djwarder
Hey, this sounds like a pretty nice idea. An example file would be great if that's possible?

Peters solution above is much better and more proper but this is a quick solution for simple situations

Nice Peter!!! Thank you!!

Anyone have a simple working example file of the vopsop method for transforming high res geo - as described by pclaes? I am having trouble creating it.
Thanks
Stephen

+1

Whats really cool about the method pcales mentioned is that you can smooth out the Quat -> matrix values with an attrib blend. So if your pieces are constrained together their edges stick together giving a cloth/metal vibe to them.

As of 12.5, the Transform Pieces SOP will do exactly this transformation.

http://www.sidefx.com/docs/houdini13.0/nodes/sop/xformpieces [sidefx.com]

johner
As of 12.5, the Transform Pieces SOP will do exactly this transformation.

http://www.sidefx.com/docs/houdini13.0/nodes/sop/xformpieces [sidefx.com]

yay, thnx man, everything just got a lot easier.

I think this kind of solutions should be more prominently mentioned. I know this node skipped under my radar for almost a year

Netvudu
I think this kind of solutions should be more prominently mentioned. I know this node skipped under my radar for almost a year

Fair point. I've attached a simple example of transforming hi-res fractured geo from a low-res RBD simulation. This will be an example for the Transform Pieces help for tomorrow's build.

By the way, Transform Pieces actually shows up in the Point Replicate SOP: all the points are created and sampled at the origin then transformed by the template points using Transform Pieces. POP Replicate is also based on Point Replicate, so Transform Pieces gets a fair bit of use, just somewhat hidden.