2

We tried solving a static equilibrium problem between two boxes:

static_equilibrium_problem = StaticEquilibriumProblem(autodiff_plant, autodiff_plant.GetMyContextFromRoot(autodiff_context), set())

result = Solve(static_equilibrium_problem.prog())

And got this error:

RuntimeError: Signed distance queries between shapes 'Box' and 'Box' are not supported for scalar type drake::AutoDiffXd

Is there more information about why this doesn't work, and how to extend the Static Equilibrium Problem to more general boxes and even meshes?

My guess is the SDF collision query between boxes is not differentiable for some reason, although it works for spheres: https://drake.mit.edu/doxygen_cxx/classdrake_1_1multibody_1_1_static_equilibrium_problem.html

EpsilonGreedy
  • 83
  • 5

1 Answers1

0

The primary reason is the discontinuity in the derivatives. We haven't decided what we want to do about it. While SDF is continuous, it's gradient isn't inside the box. I'd recommend posting an issue on Drake with your use case, and what kind of results you'd expect given the mathematical properties of SDF for non-smooth geometries (e.g., boxes, general meshes, etc.). The input will help us make decisions and implicitly increase the importance of resolving the known open issue. It may be that you have no problems with the gradient discontinuity.

You'll note this behavior has been documented for the query. However, you'll note for the mathematically related ComputePointPairPenetration() method, we have additional support for AutoDiffXd (as documented here).

But the issue is your best path forward -- we've introduced some of this functionality based on demonstrable need; you seem to have that.

Sean Curtis
  • 1,425
  • 7
  • 8