Forums Technical Discussion DOP Not following alembic object animation.

DOP Not following alembic object animation.

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Arakismo
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Hey,

I'm pretty new to Houdini and I got a problem with one of my simulation: I imported an animated alembic object and want to do a water sim that follow the animation. I searched a lot and the only thing I found partially working is the Rivet node, so I imported the same object 2 times and used one as the rivet parent.

The problem is that the child don't follow the orientation, only the translation because it's on a point. Is there any simple way to solve this?

It's weird that everything (Collision, isooffset,velocity volume) follow perfectly excepte de DOP Network, if anyone can give a reason behind that I'm interested.

Thanks in advance!
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Arakismo
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Here is a quick preview of the problem:
It's supposed to follow the translation AND orientation like the blue outline show.
Edited by Arakismo - Nov. 14, 2018 08:52:32

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Houdiniproblem02.PNG (374.6 KB)

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Arakismo
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okay so apparently I can rivet it to multiple point so it follow the orientation too, but I only see one point on my mesh (0), probably because it's an alembic, anyone got an idea on how to fix that? Oo
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jsmack
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You don't use a rivet with alembic, you have to unpack it first. Normally you don't need to unless it is deforming, as transforming geometry should have it's transforms stored in the alembic. You can access the transforms using the Alembic Transform object node.
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Arakismo
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Thanks for the reply, is the ‘'Alembic Transform’' you're talking about = Alembic Xform? I don't see any node with the same name as that at object level.I unpacked the alembic used in the rivet and now I see the points but when I select all of them it doesn't match at all, so yep rivet is probably not the way there. Here is what the node look like inside:




And outside:

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Houdiniproblem04.PNG (72.1 KB)
Houdiniproblem05.PNG (93.0 KB)

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jsmack
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Yes, ‘Alembic Xform’. Xform=Transform, I don't even see them as different words anymore.
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Arakismo
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okay I'm going to try it. Thanks!
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Arakismo
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After many try it's still not working, Tried to import with the alembicXform and then using ch(“../alembictransform/fetchworldxform”)on location and rotation but the DOP is still not following. (If the alembicxform have the translation/rotation stored in it, why do ch(“../alembictransform/tx”) is not available? This problem is insane, if only it worked with a simple parent link…

Here is what it look like:

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houdiniproblem.PNG (63.1 KB)

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Arakismo
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Blue=follow the alembic animation perfectly
Red=don't follow

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jsmack
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The alembic transform stores the transform in a matrix, it's not accessible as trs that way. You can use python to get the matrix and crack it, but wouldn't it be easier to parent your object to the alembicxform node (that's what wires do in object land).

http://www.sidefx.com/docs/houdini/basics/objects.html#parenting [www.sidefx.com]
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Arakismo
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Thanks for the reply, good to know that the xform are stored this way. I already tried a simple parent link and fetch/blend/extract transform but nothing work. When I parent it with a simple link everything inside the graph follow except the DOP, it look like the DOP take his transform from another source than any other node. Mayby with python like you said? But I'm not a vex/python expert so if you could provide an exemple that would be really helpful! Recreation of my scene with an animated box included
Edited by Arakismo - Nov. 28, 2018 11:45:45

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HoudiniDOPProblem.hipnc (617.0 KB)

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