[Idea] Add support for sensor origin in vehicle definition json file for carla_spawn_objects

[ksuszka]

We have a physical vehicle for which we created URDF file with sensor definition. In our URDF the reference point on the vehicle is the middle of the rear axle and it is called base_link according to ROS convention. We created the 3d model of our vehicle in Carla to test its behaviour in a simulated environment. However due to Carla requirements, the origin point of the 3d model is on the ground in the middle of the vehicle. As vehicle.json definition file consumed by carla_spawn_objects uses the 3d model origin point we need to manually recalculate the virtual sensor position for it to match the physical sensor position.

So there is this idea to add to the vehicle.json additional origin node with a 3d transformation which would be applied to all spawn points defined in this file. So in our case we would define base_link->origin translation in this node and all sensor positions would be defined referenced to the base_link.

What do you think about this idea? Would you welcome PR with an implementation?