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Writing Alembic Properties, time scaling issue

Message 1 of 14
1411 Views, 13 Replies

Writing Alembic Properties, time scaling issue

So I'm trying to write some properties to an alembic cache, strands from bifrost specifically. The properties are animated, and I'm trying to bring them over to Houdini. The problem is there seems to be time scale issue in Houdini. When I run abcinfo on them, I can see the points P[3] have some time data on them

(animated[66]) t0=41.7083 (frame 1001.0 @ 24fps)

How can I include that kind of data on a custom property I wrote to the strands? on my custom property it just says (animated), but not any time information at all. Since the write_Alembic compound doesn't expose much to the user, I'm not sure how to achieve this

Message 2 of 14
in reply to: bugsdabunny

I've also tested it out import it into Maya (not bifrost) and it still has the same issue. Oddly enough, if I read the alembic cache in through a bifrost file_cache node then it shows up correctly

Message 3 of 14
in reply to: bugsdabunny

Ok it seems to me there is no way to write time sample data to properties through bifrost. The only solution I found right now is to manually set it after export. Here is where I read about a solution

Message 4 of 14

@bugsdabunny I would like to understand what feature you are missing a bit better so we can log a feature improvement. Can you go into a bit more detail about what you need?

Message 5 of 14

Hi @morten.bojsen-hansen, sure thing. When I try to write a custom property to an alembic cache in bifrost using set_geo_property I think the Time Sampling of the property is missing. It is only missing for any custom properties, and I have only tested it on strands. I'm writing a static property below just as an example, but usually I am writing animated properties which aren't animating properly when importing the alembic cache outside of bifrost.


Screen Shot 2021-04-16 at 2.52.49 PM.png


The point_positions of the strands are being written into whatever is the equivalent in an alembic curve cache, and that property includes the right time sampling (24fps in my case). The time sampling does not seem to be included for custom properties as far I can tell, so when importing it into Maya (not through bifrost) or Houdini, the property has no sense of how often its sampled and will yield an incorrect result. The workaround in Houdini was to retime the values manually, but this seems a bit of a hack. Also, when reloading the alembic cache through bifrost's file_cache node it was the correct result, contradictory to loading in Maya (not through bifrost) or Houdini.


I'm not super well versed in alembic archives and how to store them properly, so I can't go into much more detail than that. But I was reading through this to get a better sense of it: . I think the bifrost compound is already doing it for point_positions like I mentioned, just not anything else. Here is an example that was linked in the GoogleGroup:


Let me know if you need more detail

Message 6 of 14

@bugsdabunny Thank you for taking the time to explain the problem. I'll investigate the problem further.

Message 7 of 14

Awesome, thank you very much!

Message 8 of 14

@bugsdabunny I have verified that this is a bug in Bifrost. I have logged BIFROST-5889 to address this issue. Hopefully we can fix this soon.

Message 9 of 14

That sounds great. Is there a tracking page for bugs like this, for the public to check the status?

Message 10 of 14

You can look for the bug in the release notes.

Message 11 of 14

The bugfix should be in the next release.

Message 12 of 14

Awesome, great news. Thanks!

Message 13 of 14

@bugsdabunny, All the time sampling issues should be fixed in Bifrost just released!

Message 14 of 14

Awesome, sounds great!

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