mesh with colour

[christian-rauch]

It seems that the information about the colour of a mesh has to be transported separately from the points and faces:

• MeshGeometry.msg only contains the vertices/points, their normals, and the faces.
• MeshVertexColors.msg contains only a list of colours.
• MeshTexture.msg for a texture.

Is it a deliberate choice to have the information split across several messages? How should someone combine the colour and texture with the mesh?

Have you thought about a single message definition with optional fields for the colour or other attributes, like for PointCloud2?

The TriangleMesh.msg in the @lvr-ros repo is a good example of how this can be combined in a single message with optional fields.

[amock]

As far as I remember, there were good reasons for splitting the messages, although I can't recall all the details. The lvr-ros repository you mentioned was the first attempt. It later evolved into the message definitions currently available in this repository.

One advantage of this message structure that comes to mind is handling partial updates:

• In MeshNav, cost layers can be changed partially at runtime dependend on the parameters
• For obstacle layers (coming soon), it's essential to update specific parts very quickly.
• Some other non-geometry attributes may vary depending on the time of day.
• Textures may change dynamically. For examples if you want to have videos as textures.

If we followed a structure similar to PointCloud2, you'd have to transmit the entire mesh and all its attributes for every minor change, which would be inefficient.

Admittedly, the current setup is a bit more complex, and it might not be immediately clear to others how everything works. That's why additional high-level documentation and examples would be nice to demonstrate and test how the messages in this repository are intended to be used. I've already started working on that here: https://github.com/amock/mesh_msgs_examples . I stopped at the point where textures were involved. There are also some related issues, such as #24 and #25. However, I can't say when I'll have time to continue this.

So if anyone wants to jump in and contribute before I get to it, feel free to help!