I was working with pyro in houdini, converting it to vdb and importing it into ue after exporting. But as you can see in the gif, this volume was moving on its own, it looked like it was moving every time the bounding box got bigger.

After hours of trying to figure out why, I realized that this behavior coincided with the timing of the transform matrix value of intrinsic on a volume created in houdini.

When I forced this value to identity matrix in houdini, I was able to see the same behavior I was seeing in UE5.3.

So far, my theory is that the vdb I exported from houdini doesn’t recognize or ignores the transform matrix in UE5.3 for some reason.



Here is a vdb with the same pyro solver, but the difference between them is the use of
'gas resize fluid dynamic dop'.
The first gif is a bounding box that has not been re-dynamic resized but is fixed in sufficient size, and the second gif is re-dynamic resized.

When I checked these two vdb in the geometry spreadsheet, this issue was occurring at the UE depending on whether the transform attribute of the intrinsic was fixed or not.




Just in case, I forcibly changed the transform attribute into a unit matrix, but it was meaningless, and even if I newly configured the bounding box through the vdb combination, the transform attribute was still moving in flux.


In the end, Houdini needs a way to determine whether pyrovdb cannot be sent to UE using a sparse solver, or how to modify the transform intrinsic to come out as intended.



(This issue is the same question that was posted on UE dev forum)
https://forums.unrealengine.com/t/openvdb-is-moving-around-on-its-own-on-ue5-3-transform-forcibly-recognized-as-a-identity-matrix/1322031?u=dsharp_k [forums.unrealengine.com]