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ArnoldUsdChaser seems to affect camera film back size

Message 1 of 7
82 Views, 6 Replies

ArnoldUsdChaser seems to affect camera film back size

Hi there, I'm having a weird issue exporting a camera from maya to USD using the Arnold plug in configuration and I was hoping someone here might be able to nudge me in the right direction. So far I have been testing using:

  • maya-2024.2
  • mtoa- and mtoa-
  • maya_usd-0.27.0
  • Rocky Linux 8.7

To reproduce this issue I have been:

  • Opening maya.
  • Creating a new camera.
  • Running this code snippet:


import os
import maya.cmds
selection =
maya.cmds.mayaUSDExport(selection=True, file=os.path.expanduser("~/arnold.usd"), jobContext=["Arnold"], worldspace=True)
maya.cmds.mayaUSDExport(selection=True, file=os.path.expanduser("~/no_arnold.usd"), jobContext=[], worldspace=True)


  • Loading the two usd files back into maya in the USD Layer Editor.

When I do this, the aperture dimensions of the two cameras appear to differ; on my end the no_arnold camera is 36x24, and the arnold camera is 51.429x38.571. The original camera in my scene has film back dimensions matching the no_arnold scene, 36x24. This is problematic for my workflow because it changes the field of view of the camera and the framing of my scene when I export a camera using arnold. 


I've had a go at stepping through ArnoldUsdChaser.ExportFrame with the python debugger and as far as I can see the camera in the USD stage initially has the correct film back dimensions (matching what I have in my maya scene) until this call


cmds.arnoldScene('', usd_cache=self.stageId.ToLongInt(), usd_mask = mask, options = _optionsNode)


after stepping over this line my camera in my USD stage seems to have the aforementioned incorrect film back dimensions.


I've not yet had any luck finding information about cmds.arnoldScene, I'm guessing this might be an internal bit of the API? Does anyone know why I am seeing this behaviour?

Message 2 of 7

I've just tested with mtoa- and I'm observing the same behaviour here.

Message 3 of 7

This is logged as MTOA-1951
USD export sets wrong vertical and horizontal aperature values

// Stephen Blair
// Arnold Renderer Support
Message 4 of 7

Ah, thanks for confirming Stephen!

Message 5 of 7

Oh, and arnoldScene is a Maya command implemented by MtoA. It gets the Arnold nodes for a scene.
Mostly used internally. You can get quick help in the script editor to find out what flags it takes.

// Stephen Blair
// Arnold Renderer Support
Message 6 of 7



Thanks for the tip. I think I may be missing something here, if I run (python)




I get 


Help on function arnoldScene in module maya.cmds:

arnoldScene(*args, **keywords)





help arnoldScene


gives me a bit of a more detailed result


// Result: 
// Synopsis: arnoldScene [flags] [String...]
// Flags:
//    -l -list       String
//    -m -mode       String
//    -o -options    String
//    -q -query     
//    -s -session    String
//   -uc -usd_cache  Int
//   -uf -usd_frame  Float
//   -un -usd_name   String
// Command Type: Command


is there any way I can get a bit more info about what these flags do, do you know?


Message 7 of 7

No, there's no more information, except possibly some example usage in the Python files that ship with MtoA. 

// Stephen Blair
// Arnold Renderer Support

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