Publish sim GPS information

[eomielan]

Purpose

The purpose of this issue is to update the physics engine node to publish mock GPS data for the boat's current latitude, longitude, speed and heading.

Description

Update the __publish_gps() and __publish_kinematics() functions in the physics engine node to publish mock latitude and longitude with added noise.

The longitude is represented by the x component of the global position vector and the latitude by the y. You can access this global position through the self.__boat_state attribute in the node. To add noise you can use the SimGPS sensor, where you can use the setter to update the current lat_lot and the getter to retrieve it with added noise.

The speed can be calculated by taking the magnitude of the boat's global velocity.

For heading you can simply publish the global angular position. This can also be obtained from the boat state.

[alberto-escobar]

GPS values will be calculated from SimGPS. When instantiating SimGPS feed it the values of global_position from BoatState and also speed and heading which are calculated from velocity from BoatState.