[Question] Rollout times with plane terrain vs flat generator terrain

[ShfPeleg]

Question

I have a dramatic increase of rollout time (roughly twice as long) when running simulations with a terrain (either heightfield or mesh) compared to the plane. I tried changing the size, number of rows/cols, the horizontal_scale, vertical_scale and the slope_threshold.

I understand that there are more calculations to be made when using the generator but the increase if almost twice the time. But is this a normal behavior? Anyone had this phenomenon as well and was able to reduce it?

Thanks!

[RandomOakForest]

Thank you for posting this. While some increase is expected due to the complex collision checks and physics calculations required for uneven terrain, an excessive jump may hint at optimization opportunities or non-optimal terrain representation. Performance degradation of up to 2x compared to a plane is generally considered normal, especially for mesh terrains with default physics settings. Here are some steps to consider:

• Lower heightfield resolution: Reduce rows and cols—even small reductions can help if the terrain detail is not critical.
• Downsample mesh terrains: Use simplified meshes with fewer vertices and triangles to minimize collision checks.
• Terrain segmentation: Divide terrain into smaller, locally loaded pieces if full terrains are not required for every environment.
• Tune physics engine parameters: Experiment with solver iterations, contact offset, or enable/disable features like mesh cleaning or continuous collision detection if they are not essential.
• Profile simulation: Use built-in profiling tools (e.g., Isaac Sim's Physics Profiler) to determine bottlenecks within terrain processing versus robot physics.
• Parallelization: Ensure you're maximizing GPU or CPU parallel environments—some performance loss is offset by parallel rollout if hardware allows.
• Switch collision type: If possible and accuracy is sufficient, use the heightfield primitive instead of mesh, as heightfields are spatially indexed and faster for collision detection.

[ShfPeleg]

Hi! Thanks for the response.
Currently I only use the grid with sub-terrains. Is there another way? I tested from 1X1 grid with size 16,16 to 128X128 with size 4,4 and haven't seen any real change in the time.

When you are referring to Lower heightfield resolution, is that to the sub-terrain grid or the actual resolution in each cell? If so where do I change it?

Another question, is that I saw that there is the @height_field_to_mesh decorator so aren't both methods equivalent?

[vassil-atn]

I've noticed the same thing, and I feel like mesh terrains are significantly slower than a few releases ago. I think it also depends on the GPU being used - for example on an RTX 3060 it takes <2s for a plane rollout of 24 steps, and ~10-12s on the default rough locomotion terrain (5-6x slower).