This ROS package, gps-sim, provides a ROS service for mapping from a local projected (specifically UTM) coordinate reference frame to WGS-84 geographic coordinates and representing them as pseudo (faked) NMEA sentances for simulating field robots.
Projected coordinate systems express position a North, East, Up (NEU) reference frame from a reference location. The reference location must be defined as a ROS parameter. as shown in the follow python code snippet:
rospy.set_param('/geodesy/LatOrigin',43.0)
rospy.set_param('/geodesy/LonOrigin',-70.0)
Gps-sim assumes the proejcted coordinate system is the UTM zone of the LatOrigin and LonOrigin. When a PoseStamped message is sent to the gps-sim service with coordinates in the given UTM zone the service will respond by publishing a pseudo GPS NMEA string to nmea_msgs/Sentence