Import URDF not working as expected

HI,

I’m trying to import the LeoRover description in Unity using ZeroSim. I followed the video tutorial and the comment from @micahpearlman in https://github.com/fsstudio-team/ZeroSimROSUnity/issues/17#issuecomment-995344947. I was able to import the .obj files but it looks like the joints weren’t imported properly.

Have I missed something or is this the expected behaviour?

Setup info:

• Unity 2020.2.6f1
• on Ubuntu 18.04 LTS
• with your docker image to convert the meshes

Thanks, Alex

[ghost]

No problem, that’s what open source is for!

We appreciate that you released ZeroSim to the public. I have experience with ROS and linux, but at the moment I have no experience whatsoever with Unity and C#. I have a colleague that’s got the opposite set of experiences. It sure is a possibility for us to contribute back to ZeroSim.

[ghost]

Thanks for you patience as well, I’m quite fluent, but English isn’t my first language so there might be some stuff that’s lost in translation.

FYI: xacro is just an xml macro language on top of the urdf xml. It makes life easier when you want to add links and joints in a modular way. As an example, this is the file that i use to add parts to the LeoRover original URDF:

<?xml version="1.0" encoding="utf-8"?>
<robot xmlns:xacro="http://www.ros.org/wiki/xacro">
    <xacro:include filename="$(find leo_ssom_addons_description)/urdf/e_stop.xacro" />
    <xacro:include filename="$(find leo_ssom_addons_description)/urdf/mounting_plates.xacro" />
    <xacro:include filename="$(find leo_ssom_addons_description)/urdf/realsense.xacro" />
    <xacro:include filename="$(find leo_ssom_addons_description)/urdf/jetson_nano.xacro" />
    <xacro:include filename="$(find leo_ssom_addons_description)/urdf/rplidar.xacro" />
</robot>

Link origin issue

I believe you found the root cause of the issue. To my knowledge, the link origin rotations and translations values aren’t used when importing the URDF. I think that it could be handled in the conversion script probably with bpy.ops.transform.rotate(rpy) and bpy.ops.transform.translate(xyz). I guess it might also be handled here: https://github.com/fsstudio-team/ZeroSimROSUnity/blob/9adff2a83fb4cb9ec4207ca7e933ca56ae5ad01f/Runtime/Scripts/Util/ImportExport/ZOImportURDF.cs#L113 and there: https://github.com/fsstudio-team/ZeroSimROSUnity/blob/9adff2a83fb4cb9ec4207ca7e933ca56ae5ad01f/Runtime/Scripts/Util/ImportExport/ZOImportURDF.cs#L213

I investigated by opening my .dae file in Blender.

I then manually applied the <origin rpy="0 0 -1.57079632679" xyz="0.155 0 -0.0085"/> rotations then translations.

The origin is now where the URDF is expecting it.

Validation in Blender with joint origin applied

After import

After joint origin is applied the part is properly located and the joint is where it’s expected to be. <origin rpy="0 0 0" xyz="-0.045 0 0.0085"/>