STL will not load in rviz (from urdf)

Question

I try to include an stl in im urdf file, but not succeeding so far. What I've tried:

roscore

rosparam set /robot_description -t data/models/urdf/cube.urdf

rviz -> in rviz add RobotModel

With a basic cube geomety it works, I can see the cube. But when I swop it with an stl it stops working (I tried different stls). With this it works:

<?xml version="1.0"?>
<robot name="box">
    <material name="black">
        <color rgba="0 0 0 1" />
    </material>
    <link name="base_link">
        <visual>
            <origin xyz="0 0 0" rpy="0 0 0" />
            <geometry>
                <box size="0.18 0.18 0.18" />
            </geometry>
            <material name="black" />
        </visual>
        <collision>
            <origin xyz="0 0 0" rpy="0 0 0" />
            <geometry>
                <box size="0.18 0.18 0.18" />
            </geometry>
        </collision>
        <inertial>
            <origin xyz="0 0 0" rpy="0 0 0" />
            <mass value="1.0" />
            <inertia
                ixx="0.0001" ixy="0.0" ixz="0.0"
                iyy="0.0001" iyz="0.0"
                izz="0.0001" />
        </inertial>
    </link>
</robot>

But when I swop

            <geometry>
                <box size="0.18 0.18 0.18" />
            </geometry>

with

            <geometry>
                <mesh filename="file:///home/me/models/meshes/engine.stl" />
            </geometry>

it doesn't. When I remove the file:// or define a wrong path it complains. With this code there is no error, but I don't see anything in rviz. I use ros noetic.

Answer 1

Have you tried using

<geometry>
    <mesh filename="package://<my-description-package>/models/meshes/engine.stl"/>
</geometry>

my-description-pacakge should be replaced with the proper name of the description package that you created. Conventionally, this is where you store your meshes under the meshes directory.

EDIT: Make sure that you indeed install this meshes directory in your install space, otherwise it might not be detectable.

Answer 2

The issue was that the stl was in mm and I had to use

            <geometry>
                <mesh filename="file:///home/me/models/meshes/engine.stl" scale="0.001 0.001 0.001"/>
            </geometry>

to scale it down for ROS which seemed to expect m. That is why I did not get an error and wasn't able to see it.