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URDF for a sphere

asked 2012-01-29 18:20:25 -0500

I am learning URDF, when I tried making a sphere;

<?xml version="1.0"?>
<robot name="myfirst">
  <link name="base_link">
    <visual>
      <geometry>
        <sphere radius="1.0"/>
      </geometry>
      <material name="green">
            <color rgba="0 1 0 1"/>
      </material>
    </visual>
  </link>
</robot>

All I get is something more like a polyhedra;

image description

Is there any way to get a better sphere ?

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2 Answers

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answered 2012-01-30 02:02:09 -0500

updated 2012-01-30 04:18:01 -0500

I'm also not aware of a way to change the tesselation of the built-in primitives in rviz. Using an external mesh works fine, however. I've used the default sphere you can add in Blender (32 segments, 16 rings) for the image below. I scaled it and set it to smooth shading (and converted to triangles before exporting to .dae to prevent bugs as mentioned here).

Gazebo on the left, rviz on the right:

image description

/edit: Two versions of a COLLADA sphere are available here. One is using 32 segments/16 rings, the other 16 segments/8 rings.

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Stefan Kohlbrecher Thank you, kindly do me a favour - can you please send the files across to my email ? arkapravobhaumik at gmail dot com
Arkapravo gravatar image Arkapravo  ( 2012-01-30 02:41:50 -0500 )edit
See the updated post above :)
Stefan Kohlbrecher gravatar image Stefan Kohlbrecher  ( 2012-01-30 04:18:44 -0500 )edit
Arkapravo gravatar image Arkapravo  ( 2012-01-30 14:18:10 -0500 )edit
0

answered 2012-01-30 00:21:23 -0500

DimitriProsser gravatar image

As far as I'm aware, there is not - at least not with the Gazebo default shapes. You could create your own mesh file and use that instead.

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@DimitriProsser I was thinking of doing that, but if it is a problem of resolution then it will stay even with a custom made mesh ! (I have used other designing softwares, as Pro-Engineer and have got wonderful spherical shapes)
Arkapravo gravatar image Arkapravo  ( 2012-01-30 00:42:56 -0500 )edit
I think you have a misconception here, it's the default primitive in rviz that has relatively coarse tesselation. If you use a sphere with finer tesselation (for example easily done as a .stl or .dae in Blender) it will also look a lot better in rviz.
Stefan Kohlbrecher gravatar image Stefan Kohlbrecher  ( 2012-01-30 01:29:57 -0500 )edit
@Stefan Kohlbrecher Cool, then it may be worth a try !
Arkapravo gravatar image Arkapravo  ( 2012-01-30 01:32:08 -0500 )edit
to clarify, for visualization, Gazebo creates a visualization mesh with 32 rings and 32 segments by default. For collision detection in ODE, a perfect sphere is assumed, switching collision geom will slow sim down in most cases.
hsu gravatar image hsu  ( 2012-02-11 05:50:49 -0500 )edit

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Asked: 2012-01-29 18:20:25 -0500

Seen: 4,605 times

Last updated: Jan 30 '12