Cylinder-Cylinder collision wrong when tilted

[guihomework]

Context:
My Lab discovered this bug while using MoveIt! (using FCL) with the Shadow Dexterous hand, which consists of several fingers close together and with cylinders to represent collision shapes

Problem:
when moving the fingers to the side, a little, even with thiner collision cylinders that offer a large gap (more than 5mm) relatively to the fingers size, there are strange collisions as seen here.

Test in MoveIt!:
to isolate the problem we created a small moveit example only with two "bars" and the problem can be reproduced. Starting from a certain angle, the collision appears. (0.13rad on both "fingers")

We redid the test by changing the cylinder primitive into a mesh of exactly the same size and same number of faces as the rendered cylinders. The problem does not happen. So it must be in the primitive.

Test in FCL:
FCL has no self test for rotated cylinders, only translated if we understood well, so we decided to add a test in FCL directly that reproduces the two cylinders primitives and adds a rotation at their base (as in the hand), first of 0.12 rad and then of 0.13 rad and the test fails indeed at 0.13.

The test is available here guihomework@b44a3aa

Analysis:
From the code, we think that the conversion of cylinder primitives into a hexagonal prism is the reason for the problem. Due to the small gap in between fingers, the larger hexagonal prisms collide before their rendered counter-part "visually" collide.

Questions:

• Can you reproduce the problem ?
• Is there a way to solve that cylinder-cylinder collision ?
• Otherwise, is there a way to augment the number of faces of the prism when cylinders are converted to meshes ?
• Or should we go for cylinder meshes directly in the model (which is then slower in other libraries like ODE used by gazebo)

thanks

[sherm1]

I think FCL needs real primitives!

[jslee02]

I haven't looked into this problem deeply, but somehow it seems the problem is gone with #154. I tested your test code here.

[guihomework]

thanks, will have a look if #154 also fixed my issue in the "real" world (understand not the simplified test case)

[jslee02]

Sure! But, it's not sure if the problem is actually fixed. If you still have the same issue, then please provide a test that reproduces the problem. It would be very helpful.

[guihomework]

@jslee02 I am so sorry to have take a year to answer.
I just checked in our system, and I don't see the issue any longer as seen in these pictures.

Collisions are now ok in our hands.

thanks.
I close this issue.