[Sidefx-houdini-list] Alembic from Houdini to Maya - transfer "N" and "v" ?

Fabricio Chamon fabricio.chamon at gmail.com
Mon Feb 26 12:48:07 EST 2018


Hey Nikita, thanks for your replies and sorry for the delay.

I continue on my quest of exchanging assets back and forth between houdini
and maya (vray). While mb is still something I'd have to further
investigate, either by working on your suggestions or by using vray
proxies, I'm making progress on other stuff like normals and multiple UV
sets.

For multi uv sets, I've found out that the houdini alembic importer maps
maya's current uv set (as found in the mesh controls section) into the
common "uv" attribute, then wipes out all data from the properly named uv
attribute. So let's say your imported mesh has 3 uvs:

- uv1
- uv2
- uv3

and your current uv set in maya is "uv2". Then you'll end up having:

- uv   (with data of uv2)
- uv1 (with correct data)
- uv2 (with no data)
- uv3 (with correct data)

I tought I'd share this, as someone might need something similar in the
future. It took me some time to figure out, and I don't know yet how much
of this is by design or if there is something going on with assets inside
my production environment.

Other than that I had to make sure all uv attributes are qualified as
Texture Coordinates, by using the attribute rename node. Now the alembic
output driver writes all data nicely, and I can read back in maya.

Anyways, I'll keep posting stuff like this, because this kind of
information is somewhat scarce over the internet.

cheers



2018-02-21 3:53 GMT-03:00 Nikita Musatov <not.a.whale at gmail.com>:

> By the way, you can solve the problem with motion blur differently. You can
> export Alembic with 2 motion sample and emulate moving by velocity. For it
> before rop alembic output node put TimeShift with expression "floor($FF)"
> after that add PointAttribute node with expression:
> float tm = @Frame - floor(@Frame);
> @P = lerp(@P, at P+@v*@TimeInc,tm);
> After that look what happens between frames.
> But this solution works fine if you render motion blur with option start
> frame (not center of frame) motion blur. For example: Start 0, end 0.3. I
> think you can rewrite expression that it will work for center of frame
> motion. But I haven't tried it and don't be sure that will work correctly.
> I hope it helps you.
>
> ср, 21 февр. 2018 г. в 9:34, Nikita Musatov <not.a.whale at gmail.com>:
>
> > Hello Fabricio. You can read about velocity on the solidangle page. There
> > are use Soup plugin for remesh geometry.
> >
> > https://support.solidangle.com/display/AFMUG/Motion+
> Vector+Source?desktop=true&macroName=center
> > I hope it help for you.
> >
> >
> > On Wed, Feb 21, 2018, 08:38 Fabricio Chamon <fabricio.chamon at gmail.com>
> > wrote:
> >
> >> Hey everyone, as the title says.
> >>
> >> I have been trying for the last days...no lucky. there might be some
> >> gotchas along the way.
> >>
> >> May somebody elaborate on what is the consistent way to transfer normals
> >> and velocities from houdini to maya via alembic **for constant AND
> >> changing
> >> topology** ?
> >>
> >> I've tried to promote N to various contexts, changing "v" to various
> names
> >> (v, vel, velocity) and types (vec3flt, 4flt).
> >>
> >> I was not able to get MB working and neither normals (viewport looks
> >> terrible, altough it kind of renders correclty).
> >>
> >> here are some images to illustrate:
> >>
> >> maya viewport normals
> >> <https://www.dropbox.com/s/eyq4igpod72xxd1/tower_viewport.jpg?dl=0> /
> how
> >> they look inside houdini
> >> <https://www.dropbox.com/s/8xtqcd0te03rc96/tower_viewport_hou.jpg?dl=0>
> >> / render
> >> comparision in maya
> >> <https://www.dropbox.com/s/rpe75bakwnuwugr/tower_render.jpg?dl=0>
> >>
> >> as for the MB, could not get it to work with any settings. (btw using
> >> redshift, with deformation blur turned on)
> >>
> >> any help is much appreciated!
> >>
> >> thanks guys
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> >>
> >
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