Help with forest slow build time

[IJ2087]

We've recently worked on a project were we used forest pro to scatter cars in the parking lot.
Upon trying to render the animation we started getting random errors on certain frames, no matter which render node rendered the frame it would always error.

I've tracked it down to a particularly slow forest pro, the build statistics for which were 1 tree/sec , build time of 66700ms for 131 items.
The forest contained 57 vrayproxy car models distributed using a reference geometry.

The strange thing is just by remove one car custom object (didn't matter which model) from the custom object list fixed the issue.
The build times improved instantly to 715 tree/sec , build time of 183ms for 131 items.

I'm wondering if we were hitting some kind of geometry limit and I wonder if there is a way to know it and test it before rendering.
In the end we just ended up with one less car type and everything is rendering fine, but to me this is not a good solution in case where we can't simply remove necessary items from the geometry list.

[Michal Karmazín]

Hi,

I'm sorry to hear that you were facing these troubles. First, let me mention that generally, we suggest using polygon or mesh models. Internally, Forest converts all items to native instances of the render engine, making it as efficient as using proxies. You can find a detailed technical explanation here. Also, using XRefs would be recommendable in many situations. Please feel free to check this "Best Workflow for a very large scene with Forest!" thread, where you can find some more tips for dealing with heavy objects/scenes. I hope you'll find it interesting.

I would suggest you check this post. It might be related - you should optimize your V-Ray proxies to be rendered as instances. If not, V-Ray takes a long time and memory to load and unload them.

Thanks in advance for any further comments on this issue you can share about it with us/our user community (in case some user(s) will run into similar troubles).

Best regards,