Maya Alembic camera

[Stefan Andersson]

As promised, here is a alembic camera exported from Maya. And I included a small gaffer scene. You can view the alembic camera in the viewport, if you in-click "view cameras", so I guess that's why it refuses to render even though it's set in the render options as a camera.

Maya 2015 sp6, "maya-native" alembic version

Gaffer 0.26.0.0

Arnold Arnold-4.2.14.0

best regards

stefan

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Stefan Andersson, VFX Supervisor

Important Looking Pirates - ILP

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[john haddon]

Thanks Stefan,
I've attached an updated file, showing how to use the Set node to get the Alembic camera into the right set. With that I can execute the ArnoldRender node and get the image I think you expect. Let us know if that is working for you...
Cheers...
John

[Stefan Andersson]

Kind of works, it reads the device aspect a bit wrong. But it renders and it has keyframes.

regards

stefan

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[clem...@themill.com]

Hi Stefan,

Did you find a way to fix that aspect ratio ?

Clement.

[Brian Meanley]

I think I'm seeing some similar things here at the moment (incorrect FOV's from alembic cameras). It isn't exactly clear to me if this is always happening though, as I thought that some of our cameras were coming through fine. I'll have dig a bit deeper tomorrow. 

For clarification, the FOV seems to be set correctly as far as I can tell (it has the correct value in there), but the resulting view is off. Out of curiosity, how is the screen window parameter calculated? Seems like this parameter might be the culprit?

-Brian

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[John Haddon]

The short answer here is that Gaffer's camera representation, as inherited from Cortex, is deficient. Rather than model a camera with film back etc, and deriving a screenWindow from that, Cortex models a camera "baked for rendering" with a screenWindow explicitly set already. If the aspect ratio of the render resolution doesn't match the aspect ratio of that screenWindow, then you'll get squashing. Instead we should be using a "film fit" rule to fit the resolution/screenWindow into the film back without distortion. The good news is that this is finally near the top of the pile for getting done...

In the shorter term, it might be useful to know that the screen window for the Alembic camera is taken directly from Alembic's own calculation :

https://github.com/alembic/alembic/blob/master/lib/Alembic/AbcGeom/CameraSample.cpp#L146

And it might also be useful to know that you can manipulate the screen window in Gaffer by using a Parameters node and adding a Box2f parameter called "screenWindow".

Cheers...

John

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John Haddon - R&D Programmer

Image Engine

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[Brian Meanley]

Thanks for the added info John.  Seeing that the screenWindow calculation is incorporating the overscan data, seemingly cleared things up pretty quickly.  In our case the screenWindow was getting extra padding because the Maya camera had extra overscan data set under the "display" section of the camera attributes. Resetting this value to 1.0 prior to publishing our cameras seems to have fixed things. 

Thanks again!

-Brian

[Stefan Andersson]

Love old threads :) 

I was was wondering if there is a “new” way of working with Alembic cameras ? I can’t get the Alembic cameras to be visible at all right now.

Regards

Stefan

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[Daniel Dresser]

I'm not sure why cameras wouldn't be showing up currently.  This is with cache files that previously worked?  ( Aside from having to muck about with the set ).  I'll double check when I'm back at the office.  What do you see in the Scene Inspector?  Are there visibility attributes in your Alembic cache?

It might interest you to know that I'm currently in the middle of an overhaul of how Gaffer handles camera parameters, particularly focalLength/aperture - this will hopefully make it more natural to work with Alembic cameras once I get that out - though I don't think this will affect visibility of cameras.

[Stefan Andersson]

This is testing a camera that has been exported from Houdini. It works in Maya but doesn't show up either in the viewport or anywhere else. I'm importing is through the SceneReader.

While on the camera subject, any suggestions on how I would had aperature_size to the gaffer camera so that I can test dof in arnold?

regards

stefan

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[Stefan Andersson]

never mind the DOF question. Works great with using the parameter node (found a old posting)

regards

stefan

[John Haddon]

Hi Stefan,

Can you post the file that isn't working for you? I've tested with other Alembic files and it is working fine...

Cheers...

John

[Stefan Andersson]

Hello John,

I don’t have internet access on my workstation,  but I’ll see if I can replicate it at home.

With 99% certainty it is a user error and not a gaffer error :)

Regards 

Stefan

[Stefan Andersson]

This is the error that the camera throws out

animCamera_take18: ignoring scaling component in camera matrix

It's bad that the camera is scaled, but shouldn't it render anyway? Maybe this is a arnold problem.

regards

stefan

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[Stefan Andersson]

never mind.... user error. The camera renders fine :) It's just a warning

regards

stefan