Supported object shapes in pinocchio

[Linjackffy]

I have a question about the supported object shapes in pinocchio. In the file link.h, class Geometry has four enum type:

class Geometry
{
public:
  enum {SPHERE, BOX, CYLINDER, MESH} type;

  virtual ~Geometry(void)
  {
  }  
};

Dose this mean that other object shapes like ellipsoid、capsule and octree supported by fcl cannot created by pinocchio‘s URDF parser?

[jcarpent]

Dear @Linjackffy,

I think the file you are mentioning is not inside Pinocchio. In Pinocchio, to handle a geometry (Sphere, Ellipsoid, Meshes, ...), we rely on an extension of the FCL library called hpp-fcl.

To simplify its usage, we've introduced a dedicated structure called GeometryObject (see https://github.com/stack-of-tasks/pinocchio/blob/66bb1bc08669497a0da3d303841e88f68b7434bb/src/multibody/fcl.hpp#L83), which stores an FCL object.

You can then happened this GeometryObject to a GeometryModel (see https://github.com/stack-of-tasks/pinocchio/blob/66bb1bc08669497a0da3d303841e88f68b7434bb/src/multibody/geometry.hpp#L23) via the method GeometryModel::addGeometryObject.

And then use the standard computeCollisions or computeDistances of pinocchio.

[jcarpent]

Concerning the URDF parsers, it is able to handle all the geometries supported by the URDF parser and the convention then. We can then load meshes but the URDF does not support for instance the concept of capsules.

In Pinocchio in fact, we made the choice to replace the Cylinders by Capsules for convenience.

[Linjackffy]

@jcarpent Sorry for my mistake. File link.h is inside urdf_model. I would use GeometryObject to handle those object shapes. Thanks for your answer!

[jmirabel]

In Pinocchio in fact, we made the choice to replace the Cylinders by Capsules for convenience.

To be more precise, the URDF parser of pinocchio will convert a cylinder into a capsule only in the case below (taken from the unit test urdf.cpp):

  <link name="WAIST_LINK0">
    <collision name="test">
      <geometry>
        <cylinder radius="1" length="1"/>
      </geometry>
    </collision>
    <collision_checking>
      <!--- This tells to pinocchio to replace the cylinder called "test"
           by a capsule with the same radius and length -->
      <capsule name="test"/>
    </collision_checking>
  </link>

[Linjackffy]

@jmirabel thanks for your prompt！

[jmirabel]

Another insight: Ellipsoids are not supported by FCL. It wouldn't be hard to implement though.