I've written out some simmed geo as .abc files for use in Maya. Maya will not read the UVs, but Houdini reads them just fine. The alembics have to be unpacked for them to show up in Houdini–thinking that was the problem, I ran them through an unpack node and re-wrote them, with the same results. The only Googling result I've found says that UVs have to be a point attribute for Maya to read them, but I've found no way to make that happen, as attribute promote screws them all up. How can I get the UVs to Maya? Attribute transfer (in Maya) from the original object (created in Maya) doesn't work, as the new geo is simmed and moving so the UVs would swim.

Thanks!

Okay, so I've tracked down WHERE the problem seems to be, just not sure how to fix it–

First off, I backed up a bit and wrote the .abc from a previous node, which is working, UVs going fine to Maya.

This is a tree, and I have a second scene that takes the simmed/repo'd/retimed .abc and creates another version with 3,000 tiny twigs on it. Because of the camera angle and the fact that this is more for silhouette purposes, they don't have to be perfect, intersecting geo is fine, &c., so I just scattered points on the simmed tree and copy/stamped a selection of five different twigs.

Writing this straight out to alembic worked, but going into Maya it also brought in 3,001 shape nodes–one for each new twig. The solution I found was to take the geo after the copy-stamp/merge and run it through a Boolean and Convert. This made it one shape node in Maya but also apparently is what squashes the UVs.

I've tried an attribute transfer of UVs from the merge to the convert, but that doesn't seem to work–they bounce every frame.

So is there a way I can either transfer the UVs (including the original twigs' own UVs) to this version or, more probably, is there a better way to make it one shape node in Maya instead of 3,001?

I don't know what your alembic export settings are, but you should be able to give all the twigs the same string “path” prim attribute and enable “Build Hierarchy From Attribute” in your rop and it defaults to use that path attribute. Then they should export as one shape node.

You should also build path attributes for any other pieces like the trunk, leaves, etc. Or if you're bringing in the tree as an alembic you can use the path attribute that it was brought in with (keep in mind to transfer the path attribute if you're unpacking the alembic too).

Okay, I used an attribute wrangle right on the stamped twigs, right before the merge with the tree:

s@path = “twig”;

and made sure that attribute came with the original tree unpacking–according to the geometry spreadsheet, at the end of the chain, every primitive has a path of either “twig” or the path that came with the .abc.

I must have done something wrong, as now Maya can't open the .abc–it crashes. Here is a screenshot of my ROP Alembic settings (other than motion blur being enabled, the other tabs are all default settings):

The alembic path should look similar to a folder structure, or even houdini's node paths. ie: /obj/geo1/file1

Reference the original alembic file structure and copy that for your twigs. Something at least like “/twig/twig”

This time I used
s@path = “/GEO_CACHE/twig”

(The tree .abc's path is “/GEO_CACHE/pointdeform1”.) It will import into Maya, but it's bringing the 3,000 shape nodes again–apparently there's something else on the ROP Alembic I need to do to get them into one shape node in Maya?

I tried here with a tree that has over 20,000 objects and set the path to “/GEO_CACHE/twig” and maya read it as one object. Can you post a .hip file?

Indeed!

I still haven't gotten a 100% solid approach using alembic, each situation seems to have different quirks. But you were packing the twigs then putting the path attribute on packed geo and I guess alembic doesn't like that. If you don't pack your twigs then it works as one object.

You are my favorite person. I turned off the packing on the copy/stamp and a three-frame render is working beautifully–now I'm cooking down the 500-frame version, then champagne will be imbibed.

Thanks!