SpherizedURDFGenerator

An automatic C++ only tool for generating spherized / convex version of collision geometry and write URDF automatically.

Introduction

Spherized

Specifically, the term Spherized refers to sphere tree approximated collision.

Notice: the following steps are adopted to generate a spherized version

1. Watertight check (if not watertight, one will be generated)
2. Simplify (Optional; using igl:decimate to down-sample surfaces into 30%)
3. Spherized Version Generation(Several hyper-parameters can be tuned. See config/sphereTree/sphereTreeConfig.yml)

​

Convex

Specifically, the term Convex refers to convex hull approximated collision.

Notice: cgal::convex_hull() are used.

​

URDF

We only accept stl & obj file for raw collision meshes; All generated meshes are stored in obj file.

All elements and formats are followed. The generated URDF file will only modify the collision element. For Spherized version, several or only one sphere are added; For Convex version, the collision mesh will be generated, stored and correctly referred.

We only accept and generate URDF as .urdf. If a .xacro is utilized, please refer to some other tools like (pip install xacro)

python -m xacro your_file.urdf.xacro -o output_file.urdf

Dependencies

This package relies on binary-distributed libraries:

• cgal
• urdfdom
• yaml-cpp
• tinyxml2
• gmp

Fortunately, they can be installed through simple apt-get process.

sudo apt-get install libcgal-dev liburdfdom-dev libyaml-cpp-dev libtinyxml2-dev libgmp-dev

The distribution also contains the following sources from other people (some are introduced in a header-only manner):

• libigl
• plog
• sphere_tree
• ManifoldPlus
• cmake-template

This work is built on the basis of those fantastic works. We thank all the aforementioned open-source project for the help of the implementations.

Compile

cmake -B build . -DCMAKE_BUILD_TYPE=Release
cmake --build build 

Usage

Spherized

cd build && ./spherized -i <input_urdf_path> -o <output_urdf_path> [-r <key> <value> ...] [--single_sphere <0|1>] [--simplify <0|1>]

• -i <input_urdf_path>: Specifies the path to the input URDF file.

• -o <output_urdf_path>: Specifies the path to the output URDF file.

• -r <key> <value>: Specifies replacement pairs. You can use multiple -r options to define several key-value pairs that will be replaced in the URDF file.

  ​ **An useful replacement pair for ROS is “package:/” “/home/xxx/xxx_ws/src”. ** This will help this program to replace the original “package://yyy/mesh/zzz.stl” into “/home/xxx/xxx_ws/src/yyy/mesh/zzz.stl” to correctly find the mesh file without ROS. Meanwhile, the generated URDF will generate the mesh URL using the original format like “package:/yyy/mesh/zzz.obj”. So it can be directly valid for ROS

• --single_sphere <0|1>: Indicates whether to generate a single sphere approximation of the URDF. Use 1 to enable and 0 to disable.

• --simplify <0|1>: Indicates whether to simplify the URDF generation process. Use 1 to enable and 0 to disable.

Convex

cd build && ./convex -i <input_urdf_path> -o <output_urdf_path> [-r <key> <value> ...] [--single_sphere <0|1>] [--simplify <0|1>]

• -i <input_urdf_path>: Specifies the path to the input URDF file.

• -o <output_urdf_path>: Specifies the path to the output URDF file.

• -r <key> <value>: Specifies replacement pairs. You can use multiple -r options to define several key-value pairs that will be replaced in the URDF file.

  ​ **An useful replacement pair for ROS is “package:/” “/home/xxx/xxx_ws/src”. ** This will help this program to replace the original “package://yyy/mesh/zzz.stl” into “/home/xxx/xxx_ws/src/yyy/mesh/zzz.stl” to correctly find the mesh file without ROS. Meanwhile, the generated URDF will generate the mesh URL using the original format like “package:/yyy/mesh/zzz.obj”. So it can be directly valid for ROS.

Example

We use franka to test.

Preprocess

Warning: One should replace (inrobots/panda_arm.urdf)

<collision>
      <geometry>
        <mesh filename="/meshes/collision/xxx.stl"/>
      </geometry>
</collision>

into

<collision>
      <geometry>
        <mesh filename="package://franka_panda_description/meshes/collision/xxx.stl"/>
      </geometry>
</collision>

Spherized

cd build && ./sphereized -i /home/zyx/path_ws/src/franka_panda_description/robots/panda_arm.urdf -o /home/zyx/path_ws/src/franka_panda_description/robots/panda_arm_spherized.urdf -r "package:" "/home/zyx/path_ws/src" --single_sphere 0 --simplify 0

Convex

cd build && ./convex -i /home/zyx/path_ws/src/franka_panda_description/robots/panda_arm.urdf -o /home/zyx/path_ws/src/franka_panda_description/robots/panda_arm_spherized.urdf -r "package:" "/home/zyx/path_ws/src"

Citation

If this lib helps your research, please cite us

@misc{ZHOU2024SpherizedURDF,
    title={{SpherizedURDF: An automatic C++ tool for generating spherized / convex version of collision geometry and write URDF automatically}}, 
    author={Zhou, Yixuan and Wang, Hesheng}, 
    year={2024},
    url={https://github.com/IRMV-Manipulation-Group/SpherizedURDFGenerator}
}