question

This is what I did:

• In CINEMA 4D, I create an Arnold Procedural object
• That Arnold Procedural object loads the abc you provided.
• I create an Arnold shader.
• I create an Arnold Operator that uses Set Parameter to assign that Arnold Shader to a selection of the objects in the abc file.
• On the Arnold Procedural > Overrides tab, I set Mode to operator network and select the operator that I created.
• I render and it works.
• From the Operator Network, I export the operator to file
• In Houdini, I create an arnold procedural and the abc file you provided
• In the out context, I create an include graph and load the operator ass file I exported from CINEMA 4D
• In the arnold procedural node, I set Operator Graph to the include graph node.
• I render and it works.
• I go back to CINEMA 4D, and in my operator, I put in an Include Graph and load the operator ass file. That works too when I render.

Thanks for your response @Stephen Blair,

When you say: "Both these work for me (when they are in the ass file exported from CINEMA 4D and used in Houdini)"

We talk about same? I mean add .abc inside Arnold Procedural object in C4D and Houdini correct?

Both these work for me (when they are in the ass file exported from CINEMA 4D and used in Houdini)

"/objects/*Sp*_geo/*"
"/objects/Tube_mesh/*"

 selection "/objects/*Sp*"

Thanks for your response !

If you apply a selection expression without restrict it a group in the alembic, works properly in C4D and Houdini. The problem is when you want to restrict this *here_geoShape selection to works only inside /object/ group in this case (think about you have same name objects in two differents groups in alembic file /objects1 and /objects2 but you only whant to select objects inside /objects1 group)

Seems like in C4D you need to specify Arnold Procedural object ("assets" in this example), to found /object group. But in Houdini this step seems not be necessary, with /object/*here_geoShape all works correctly in Houdini. The BIG problem is when you try to solve in C4D adding /assets/objects/*here_geoShape , now C4D found /object/ group, but Houdini not...

Then, How to restrict object selections in an alembic group that work in both softwares correctly?

(to avoid false positives when you try it please, start and stop IPR everytime that you change selection expression to refresh)

Thanks!!

The attached worked for me. It puts a Utility shader on the two spheres.

Selection string is *here_geoShape (to match Sphere and Spehere in the abc file)

In Houdini:

- An arnold_procedural node that loads the abc file

- Operator graph is an include_graph

I did not try with an alembic node, and probably won't until tomorrow when it's supposed to rain...today I will be out in the yard or napping ;)

Arnold Operators.ass

In previously attached abc file you can see that objects are inside group calle "objects". Here I attach 3 look files exported:

Number 1 - Export with Selection mode "expression" and write for select spheres: /objects/*Sp*

This work ok in Houdini but no in C4D

Number 2 - Export with Selection mode "procedural" select procedural object called "assets" with abc inside and write for select spheres same expresion: /objects/*Sp*
This work ok in C4D but no in Houdini (in exported file you can see that path is really wrote as /assets/objects/*Sp*)

lNumber 3 - Export with Selection mode "expression" and write for select spheres: /*Sp*

This work ok in both C4D and Houdini.

If number 3 works on both Is very strange that number 1 only works in Houdini and not in C4D,

Thanks!

3.ass

1.ass2.ass

The problem seems be related with selection mode when you create a collection.In C4D i need select mode "Procedural", select arnold procedural element and the write expression to see changes in IPR. But when I export this look to Houdini I see nothing in Houdini IPR.

Otherwise if In collection I choose selection mode "expression" and write same expression I see nothing in C4D IPR but when I export look file to Houdini I see correclty there.

It's make no sense for me, How I can create collections to work properly in both applications?