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Re: [Paparazzi-devel] Altitude calculation

From: Felix Ruess
Subject: Re: [Paparazzi-devel] Altitude calculation
Date: Thu, 22 Dec 2011 16:54:41 +0100

Hi Loic,

you are probably talking about the rotorcraft firmware, right?

> Could someone explain the meaning of "BARO_SENS" and "UNTILT_ACCEL" in the
> airframe file?

BARO_SENS is the sensitivity of the baro, so the scaling from raw
values to real units (in this case fixed point position
The BARO_SENS in the INS section is specified with integer="16" and
hence generates a fraction with
INS_BARO_SENS_NUM (numerator) and INS_BARO_SENS_DEN (denominator).

UNTILT_ACCEL has been unnecessary and unused since 2009, as this
"untilting" is always done.
I removed it from the airframe files in the repo...

> I have a Lisa M board and I can't obtain the right altitude
> (the value rises when i move the board down, while the raw value of the
> pressure goes up).

What message are you looking at? INS?
Remember that the coordinate system of aircrafts have the z-axis pointing down!

> I tried to find where the altitude is calculated in the code, i have found
> the absolute pressure calculation in "baro_board.h," but i can't find
> altitude calculation.

function ins_update_baro() in sw/airborne/subsystems/ins.c

Cheers, Felix

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