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Re: [Paparazzi-devel] Height in telemetry messages

From: alonso acuña
Subject: Re: [Paparazzi-devel] Height in telemetry messages
Date: Thu, 8 May 2014 21:51:44 -0600

I think all you need to do is add a setting for ground_alt, for example in conf/settings/fixedwing_basic.xml  add:

   <dl_setting MAX="4000" MIN="0" STEP="1" VAR="ground_alt"/>

This will 2 things:
   - add a control in the GCS where you can see and change the value of that variable in the airborne code.
   - periodically send a message from the plane with the value of that variable

The message you need to capture is DL_VALUE. This is sent one variable at a time so you need to wait for the correct index and then take note of that value. To know which is the correct index you have two options:
  1- check in var/aircrafts/<your aircraft name>/ap/generated/settings.h where it says #define SETTINGS. Look at which position ground_alt appears. If it is at position 4 then the index is 3.
  2- if you know the current value of the variable (you can look in the GCS) then you can see in the Messages windows the DL_VALUE messages and wait until one has the correct value, then that is the index you need

Apparently the GCS does not show the correct AGL because it does not read the ground_alt value.

On Thu, May 1, 2014 at 9:53 PM, Cameron Lee <address@hidden> wrote:

I'm wondering if there is anywhere in the telemetry message sent from the plane to the ground where the height aka Above Ground Level (AGL) is sent? I see the altitude above sea level in the GPS message and something called z in the ESTIMATOR message. Both of these seem to be altitudes above sea level though.

I should mention that a height based either on the ground_alt in the flight plan or the result of NavSetGroundReferenceHere() inarchitected the airborne code would be good. Actually, is there any way that the GCS gets to know the result of NavSetGroundReferenceHere()? If so, that should be all that's needed.



p.s. The reason I'm looking for this is because our system is designed such that the onboard computer with a camera attached gets the plane's location data by listening in on the telemetry sent to the ground. Not having to specify the ground altitude in both the flight plane and the settings for our imaging code would be good.

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