[ros-users] Gazebo: get_model_state returns wrong relative pose?

[Antons Rebguns]

Hello folks,

We hit what looks like a bug in implementation of get_model_state service in
Gazebo. The scenario that we are working with is the following: imagine an
object and a robot that is always oriented towards this objects and is
certain distance away from it. We expect the object's position in robot's
coordinate frame to be, let's say, 40cm away on x axis and 0 cm on y axis.
Now if we rotate both the robot and the object by 180 degrees, we would
expect that relative position would stay the same since robot is still
looking straight at an object and it didn't move anywhere in relation to the
object, but gazebo gives us -40cm on x axis and 0 on y axis. These numbers
get weirder with different yaw angles of the robot with respect to the world
coordinate frame. So it looks like the absolute location in the world still
matters when getting the relative pose of one objects in some other
coordinate frame (except 'world'). Is there something obvious that I am
missing here?

Thanks,
Anton
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