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Re: [Paparazzi-devel] AGL and NavSetGroundReferenceHere()


From: Pascal Brisset
Subject: Re: [Paparazzi-devel] AGL and NavSetGroundReferenceHere()
Date: Sun, 09 Aug 2009 23:29:24 +0200
User-agent: Thunderbird 2.0.0.22 (X11/20090608)

Hi,

you need

   http://dds.cr.usgs.gov/srtm/version2_1/SRTM3/Eurasia/N47E016.hgt.zip

in data/srtm/

--Pascal

Martin P wrote:
Hi, thanks for answering!

What I call AGL: What is displayed in the GCS. SRTM: I have a file N47E011.hgt.bz2. I am at N47.82 and E16.88. Does this file cover my location? If yes, I would say it is available. If no, where do I get it from? I did a "Google Maps fill". Btw, the terrain here is dead level. Greetings, Martin
-------- Original-Nachricht --------
Datum: Sun, 09 Aug 2009 17:07:54 +0200
Von: Pascal Brisset <address@hidden>
An: address@hidden
Betreff: Re: [Paparazzi-devel] AGL and NavSetGroundReferenceHere()

Hi,

what do you call AGL ?
- in the airborne code, NavSetGroundReferenceHere() sets ground_alt to the current altitude (common_nav.c:84). This variable is for example use in HOME mode (nav.c:370) or in the Takeoff and Final block of the basic.xml flight plan. - in the GCS, AGL is computed by subtracting the terrain altitude (from the SRTM model ... if the file is available in data/SRTM) from the current altitude

--Pascal

Martin P wrote:
I use a flight plan with goround_alt=0 (derived from basic.xml).
After calling NavSetGroundReferenceHere(), I would expect that the AGL
is 0.
Instead, it is the altitude above sea level. The GPS mode is 3D and the
AGL varies within 3 or 4 meters.
Is this the way it should be? Should I set the ground_alt to the actual
altitude?
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