Locating sensors on a complicated mesh

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Hello, I'm trying to find the best spot to put lidars on my vehicle. To do that i want to import an stl mesh file, and then link the sensors on the vehicle mesh. The problem is that the mesh is quite complicated and I don't know how to specify the joint which is connecting sensor to the body. Is there any way to do that or I just have to check random places in the urdf file?

Any comment would be helpful.

Thank you