Hi guys,

I was wondering if anyone has bumped into this message from mantra?

mantra: Camera has non-unit scales, which may affect certain shading (i.e. volumes)

I've imported an alembic camera from maya in this case. I'm not quite sure what this message means. Is there a way to specify units on the camera? Also, the camera is not being scaled.

I do have units set to cm in houdini (instead of the default metres) if that is of any consequence.

It's not affecting my renders, but I'm curious to know more about this.

Thanks!

I think in this case ‘non-unit’ means, ‘not equal to one’.

See here: https://en.wikipedia.org/wiki/Unit_vector [en.wikipedia.org]

ie: The camera is scaled.

G

Thanks keyframe.
That explaination helps to make sense of that message.

Since it's an alembic camera that I brought in, I wasn't able to see any rotation translation or scale changes. Is there a way to read that information?

The xform is stored as a primitive instrinsic 4x4 matrix.

You'll need to cracktransform it.

Start here:
http://www.sidefx.com/docs/houdini15.0/vex/functions/primintrinsic [sidefx.com]

… and then travel through here at some point:

http://www.sidefx.com/docs/houdini15.0/vex/functions/cracktransform [sidefx.com]

There might be another more straight forward way, but sadly, I don't know it.

G

make a null a child of the camera
turn ON Keep Position When Parenting
un-parent the null
MMB to see pre-transform scales…

arctor
make a null a child of the camera
turn ON Keep Position When Parenting
un-parent the null
MMB to see pre-transform scales…

I didn't think that worked on alembic xform nodes…

Amazing if it does!

G

Thanks guys,

That is really helpful information.

I used the method of a null node and was able to extract the transformations on a few frames across the timeline and it does seem that my scale stays pretty much at 1.0, 1.0, 1.0 throughout the frame range.

So I'm still not quite sure I understand the message about non-unit scales on the camera.

It's very common at least for me to come across this problem of a scaled imported camera.

What I usually do is to use the fetch with a null node to get the position, you can use the null technique described above to get it right, and then I use a blend node between a new camera and the null and then I disable the scale after that I manually copy reference the view parameters from the original camera to this new one so I can render with it. Works every time.

I hope that helps.