Is it possible to load a pre-calculated Truncated Signed Distance Field for collision calculation?

[MishaTikh]

Intro

Hi! I'm developing a sort of surgical simulator and looking to use SDF for loading the anatomy due to many concave features.

My setup

MuJoCo 3.3.5, Python API, Windows

My question

Is there a way to load a pre-calculated truncated SDF? I built a utility that processes STL and generates a truncated SDF based on fine tuned parameters. I see that in the latest 3.3.5 version SDF is now built in and no longer a plugin.

Minimal model and/or code that explain my question

Image of my Truncated SDF field (cyan is outside, violet is inside)

Confirmations

• I searched the latest documentation thoroughly before posting.
• I searched previous Issues and Discussions, I am certain this has not been raised before.

[quagla]

That's an interesting question. Why do you want it to be truncated? We do gradient descent on the SDF for collisions, so I'm not sure if it's going to work if it's truncated. But anyway, we don't have an easier way than writing your custom plugin. We would like to support standard SDF formats like VDB natively in the future but we haven't had the time to work on it yet. But it sounds like you have an STL surface representation so you can just prescribe type="sdf" in the geom and the SDF will be calculated and stored automatically on an octree.

[MishaTikh]

Thanks for the quick response! The main goal is file size reduction. As you can see in the image, the anatomy is sparse and hollow, which leaves a lot of empty room in the envelope, and I also need a fairly dense SDF to capture all the fine features. This leads to very large file sizes if not truncated.

[quagla]

Yes that's the same idea of VDB and that's also why we use an Octree. I would be curious if you loaded the STL and used type="sdf", how much memory you would need.

[MishaTikh]

I will test and let you know
aortic_arch.zip
! Here is the raw STL file.

[MishaTikh]

Ok, maybe I was trying to solve a non-problem. The MuJoCo generated SDF is ~12mb, while it larger than the ~2mb truncated SDF it wasn't the huge file I was expecting. Thanks!