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Re: [Paparazzi-devel] Using Waypoints in GPS/absolute coordinates

From: Loic Drumettaz
Subject: Re: [Paparazzi-devel] Using Waypoints in GPS/absolute coordinates
Date: Thu, 6 Jun 2013 16:00:29 +0200


No, HOME is not always the the origin (0,0) of the relative coordinates. It is by default, but it can be moved using NavSetWaypointHere(HOME).

There are 2 user cases:

1 Flight plan origin defined at aircraft take-off position:

- All waypoints must be defined in relatives coordinates in the flight plan.
- NavSetGroundReferenceHere() is called in the flight plan to set (0,0)  at aircraft position at the begining.
- Home is at (0,0), and doesn't need to be moved.
Warning: using absolute coordinates together with NavSetGroundReferenceHere is not handled (at least in rotorcraft), so the waypoints position will be wrong.

2 - Flight plan origin defined in GPS coordinates :

- Waypoints can be defined in absolute OR relative coordinates in the flight plan
- USE_INS_NAV_INIT to true (default now in master) set relative coordinates origin (0,0) at lat0, lon0 absolute coordinates defined in the flight plan.
- NavSetWaypointHere(HOME) moves home waypoint at aircraft start position.

Any other combination are possible, but these 2 situations are the most usefull.


Hi Felix.
I take it that even if i set "USE_INS_NAV_INIT" to FALSE the ground_alt is still set from the flight plan's header values or i need to set the "ground_alt" my self?
I use a mixed flight plan where some waypoints use lat/long absolute values and some are relative so i guess that all relative waypoints are relative to the "HOME" waypoint
(taken as 0,0)

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