Publish GPS topic only at the surface

[woensug-choi]

The hector GPS sensor plugin is modified to publish data only at the surface.

Quickstart for test

1. Edit starting depth of the glider to reach the surface faster for tests, e.g. -93 to -3
   

   glider_hybrid_whoi/glider_hybrid_whoi_gazebo/launch/start_demo_kinematics_stratified_current.launch

   Line 66 in b520042

   <arg name="z" default="-93"/>

2. Launch

   roslaunch glider_hybrid_whoi_gazebo start_demo_kinematics_stratified_current.launch
   

3. Track GPS topic on another terminal window

   rostopic echo /glider_hybrid_whoi/hector_gps
   

4. Run the commanding script to drive the glider to the surface (edit path according to your machine)
   • The script will make the glider ascend and stay on the surface for about 12 seconds and descend again. (Assuming that the starting depth as -3)

   python glider_hybrid_whoi/direct_kinematics_ros_plugins/test/test_directKinematics.py
   

5. /glider_hybrid_whoi/hector_gps topic is published only when the glider is at the surface.