Alembic mesh with velocity causing distortion in v-ray proxy.

[3d@binyan]

Hi Everyone.
We've got an animated Alembic mesh with changing topology and velocity applied (made in Houdini) for rendering with motion blur in Max+Vray.
Unfortunately when we load the object in a vrayproxy the mesh seems to distort, with the distortion being stronger or weaker depending on the velocity attribute value.
If i load the same alembic file from file-import in max, or if i export the mesh again from Houdini without velocity, there is no distortion, so i guess it's the vrayproxy doing that?
I wonder if there is anything wrong i'm doing or if it's a known issue.

p.s. Normal particles seem to work perfectly fine with no "distortion" on their position.

[3d@binyan]

Here you can see the vrayproxy with the alembic file loaded in: to the right the one without velocity which has no distortion, and to the left the one with velocity attribute which shows motion blur is working, but distorting the mesh.

[^Lele^]

Sending all the appropriate data (the ABC file, in this case, i suppose) to Support would be of huge help.

[3d@binyan]

will do. I suppose it's not a well known issue then.
I believe it's a problem of how the mesh is exported from Houdini as if i tweak some alembic settings it actually works differently.
thanks

[^Lele^]

It could indeed be some sort of flavour-related issue (think for an analogy of the TIFF format and all its sub-formats, called flavours) in the way the ABC is saved out and read back in.
Houdini being Houdini, it could write anything anywhere making it appear as nigh anything else, so hey, i'm guessing that's what may happen (say, velocity X somehow going into position Y for the mesh verts. Or some such.).
But yes, it doesn't often happen.
At least in my experience, which is by no means exhaustive on the subject matter.

Would it happen the same if you saved V-Ray proxies out of houdini, instead of ABC files? (you may need to install VfH to do that. Maybe with a demo license,but i'm not sure.)
Does the ABC with velocities load fine back in Houdini, btw?
And does the same ABC imported in max work fine with motion blur too? Or does max discards the velocities entirely on import?

[3d@binyan]

Thanks a lot for your help. We've done a few tests.

We have successfully exported a V-Ray proxy from Vray for Houdini which worked well with no distortions.
The Alembic with velocity works fine when loaded back in Houdini and renders as expected.
Max's native Alembic import doesn't support velocity for motion blur even though it's visible in the import settings.

I guess we'll stick to the vrayproxy solution then, but i'd still love to find one for the Alembic format.

[^Lele^]

Thank you for the time spent!
We'll need tests of our own then, to see why that mesh was bonkered.
Would you be able to send one frame of it to me, or support (if to support, please mention this thread.)?

Also, excuse me for taking up your time like so, but how was the performance of the ABC versus the Proxy, both for export time, size on disk, and memory occupation?
I have done my tests, but i dread my own bias, hence me asking.

[3d@binyan]

These are all tests that would help us too. I've forgot to mention, we are using 3dsMax 2020.1 and V-Ray Next 2.1 for now.
I didn't have the chance to try on big files, so the size, time and memory used seem to be very similar with a slightly smaller size when using the proxy (50Mb Proxy instead of 55Mb ABC).
Another issue I've observed, which is no big deal as it's only related to the interactive render, is that in 3dsMax you need to move the keyframe in order to see the vfb updating with the changes to your camera settings (in this case, the shutter speed value).

I will send the file soon, happy to send it directly to you. How do we do this?
In the meantime, have a happy new year!

[^Lele^]

I will send the file soon, happy to send it directly to you. How do we do this?

You can upload the file where you please, and share a link with me, or i can provide you with a gdrive folder, an FTP address, whatever suits you best.

In the meantime, have a happy new year!

Likewise!

[3d@binyan]

If you could provide me a gdrive folder that would work best for me.
Thanks a lot for your help.

[3d@binyan]

Hi just to let you know I've made a new account so this is my new user.

[^Lele^]

I wrote you a PM with the link to the folder.

[Mirko.Binyan]

oops sorry i meant this account lol. that's fine i'll check on Monday
Thanks

[^Lele^]

Ahahah, mistakes on January 2 are par for the course, i believe. XD
Have a great weekend!

[Mirko.Binyan]

I have uploaded the alembic and the vrayproxy in there (tried to respond to your message with my email, but something didn't work).
You can load them both in a vray proxy object in max and can see how one is ok while the other one gets distorted.