[mavros_extras] mocap_estimate.cpp plugin

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A plugin to connect to:
vicon_bridge: http://wiki.ros.org/vicon_bridge
or vicon_mocap: http://wiki.ros.org/vicon_mocap
Must have a tf_lookup to vicon/<subject_name>/<segment_name> or ~output depending on the pkg being used.

Msg to send: VICON_POSITION_ESTIMATE
https://pixhawk.ethz.ch/mavlink/#VICON_POSITION_ESTIMATE

Note: Possible OptiTrack support can be added and message sent through VICON_POSITION_ESTIMATE. It can be connected to http://wiki.ros.org/mocap_optitrack.

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To use APM, from what I read in a source, you must use the NMEA protocol, which is the protocol used by APM to get the GPS coordinates (considering that you are using a NMEA GPS internally in APM). Writing a C code that converts local positions to global position will do the job. Here's some reference: http://en.wikipedia.org/wiki/NMEA_0183 and the APM code:https://github.com/diydrones/ardupilot/blob/master/libraries/AP_GPS/AP_GPS_NMEA.cpp.

If you are planning to use other kinds of external GPS's, you have to shut the GPS connected internally the APM: https://code.google.com/p/arducopter/wiki/GPSDisable.

The APM (ArduCopter v3.0.1) needs the following packets to work: RMC,GGA,VTG, which are defined as GPS_SENTENCE_GPRMC, GPS_SENTENCE_GPGGA and GPS_SENTENCE_GPVTG packets in the firmware respectively. Writing directly to this ones I think it's what has to be done.

@tonybaltovski If you are able to do this convertion maybe then you can also write a plug-in to mavros to get those conversions :D (only useful for APM users) PX4 doesn't support NMEA devices.

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This can be easily implemented. Follow the vision_position.cpp plugin code in mavros main master branch. You can do almost a copy paste from it i just recommend that you add a parameter to choose if we are receiving a tf or pose from a vicon bridge or a optitrack bridge, so it can be more general.

[vooon]

Plugin added, testing required.

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See #122.

[mhkabir]

Plugin works fine, can see data in PX4 side. No support for it in INAV though.

For users, please use vision_position plugin for now. It will give you the same functionality.