Tesseract  0.28.4
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URDF

Tesseract is compatible with Universal Robot Description Format (URDF), the native format for describing robots in ROS. In this tutorial, you will find resources for the URDF and important tips.

Important Tips

This section contains a set of tips on making sure that the URDF that you generate can be used with Tesseract. Make sure you go through all these tips before starting to use Tesseract with your robot.

Special Characters in Joint Names

Joint names should not contain any of the following special characters:

  • -
  • [
  • ]
  • (
  • )

Safety Limits

Some URDFs have safety limits set in addition to the joint limits of the robot. Here's an example of the safety controller specified for the Panda robot head pan joint: 

<safety_controller k_position="100" k_velocity="1.5" soft_lower_limit="-2.857" soft_upper_limit="2.857"/>

The "soft_lower_limit" field and the "soft_upper_limit" field specify the joint position limits for this joint. Tesseract will compare these limits to the hard limits for the joint specified in the URDF and choose the limits that are more conservative.

Note
If the "soft_lower_limit" and the "soft_upper_limit" in the safety_controller are set to 0.0, your joint will be unable to move. Tesseract relies on you to specify the correct robot model.

Collision Checking

Tesseract uses the meshes specified in the URDF for collision checking. The URDF allows you to specify two sets of meshes separately for visualization and collision checking. In general, the visualization meshes can be detailed and pretty, but the collision meshes should be much less detailed. The number of triangles in a mesh affects the amount of time it takes to collision check a robot link. The number of triangles in the whole robot should be on the order of a few thousand.

Test your URDF

It is very important to test your URDF out and make sure things are configured properly. Consider using the ROS check_urdf tool to validate your URDF.

Tesseract URDF Extensions

Tesseract provides several extensions to the URDF standard.

tesseract:capsule

Capsule geometry

URDF path: /robot/link/<visual|collision>/geometry/tesseract:capsule 

<tesseract:capsule length="<float>" radius="<float>">

tesseract:cone

Cone geometry

URDF path: /robot/link/<visual|collision>/geometry/tesseract:cone 

<tesseract:cone length="<float>" radius="<float>">

tesseract:octomap

Octomap geometry, populated by an octree or point cloud

URDF path: /robot/link/<visual|collision>/geometry/tesseract:octomap 

<tesseract:octomap shape_type="box | sphere_inside | sphere_outside">

Nested elements:

tesseract:octree

Octree file source for octomap geometry

URDF path: /robot/link/<visual|collision>/geometry/tesseract:octomap/tesseract:octree 

<tesseract:octree filename="*.octree">

tesseract:point_cloud

Point cloud file source for octomap geometry

URDF path: /robot/link/<visual|collision>/geometry/tesseract:octomap/tesseract:point_cloud 

<tesseract:point_cloud filename="*.pcd" resolution="<float>">

tesseract:sdf_mesh

Signed distance field (SDF) mesh geometry

URDF path: /robot/link/<visual|collision>/geometry/tesseract:sdf_mesh` 

<tesseract:sdf_mesh filename="*.sdf">

tesseract:make_convex

For convenience, Tesseract can automatically convert collision mesh geometries into convex hulls for more efficient collision checking and motion planning. Set the tesseract:make_convex attribute(s) to enable this behavior.

Note
It can be convenient to use this attribute to convert collision meshes into convex hulls, but convex hulls often overapproximate the original geometry. It is highly recommended to visualize the collision geometry of the Tesseract environment before motion planning to ensure it is not overly conservative.

Global (Required)

URDF path: /robot/@tesseract:make_convex="true | false"

Mesh-level override (Optional)

URDF path: /robot/link/<visual|collision>/geometry/mesh/@tesseract:make_convex="true | false"

Note
Setting this attribute at the mesh level overrides the global setting

Additional Resources