alembic particles from houdini, UV mapping. ?

[super gnu]

i can export a particle cloud from houdini as alembic, and tell it to include the UV attribute. however when i check with ply2vrmesh, it says "uv channels:0" "colour channels: uv"

so i did some reading, and it seems that uv mapping on points rather than vertices is a houdini specific thing, and other applications cannot read it?!

they recommend using an "attributepromote" to convert the uv point data to vertex data.. but that was for geometry. i dont have any vertices...


please tell me there is a way to get vray to read and use the UV point attribute?


particularly important as if its a houdini solution, there is a slim to none chance ill get a reply on their forum.. its a ghost town. which is odd for such a mindblowing bit of software.

[super gnu]

hm. nobody? vlado? i can send you an alembic with point uv coordinates if it would help?

[kagemaru]

Apparently there's something not reading correctly with the uv attribute per se once exported, but you can hack it in this way:
- in houdini after you have your uvs, create an attributevop and plug the uv in the Cd.
- export the alembic.
- you should have now 2 channels, in the vrayproxy under "compatibility" check the "force first map channel" and set it to 0: in this way it'll use the Cd attr as vertex color.
- set your texture mapping to Vertex Color Channel et voilà, you have your uv transferred.
Hope it helps.

[super gnu]

thanks a lot for the reply, im quite a noob in this whole houdini thing. seem to be a lot of us around at the moment.. its an amazing bit of software but rather hard to get your head round!

anyway, your advice sounds good.. although, im using the Cd attribute to get individual particle colours out.. i need the uvs for a texture i wish to blend over this. i assume that means i cannot use the Cd attribute for my UV data.

[kagemaru]

Ok so no worries, apparently i don't know why but if the attribute is set to vector3 as [0],[1],[2] vrayproxy doesn't recognize it as vector color, so instead of using Cd create your own attribute, let's say "myUv" with an AttributeCreate, set it to Vector and plug your uvs in there. You should see it in Houdini as [x],[y],[z].
Use this channel in the "force first map channel" and it's going to work.