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Re: [Paparazzi-devel] PPRZ Complementary Filter

From: flavio_just
Subject: Re: [Paparazzi-devel] PPRZ Complementary Filter
Date: Mon, 28 Dec 2015 08:52:08 -0700 (MST)

Thanks so much Hector,
I will try to understand the equations step by step. I am a bit familiarized with Mahony's work. Actually the goal of the work I am doing is to implement in PPRZ a Trace Based Filter that was developed in my faculty and this filter is mostly based on the trace maps that Mahony defines. I will ask you further questions if I need =) Thank you so much!

2015-12-28 8:52 GMT+00:00 Hector Garcia de Marina [via Paparazzi UAV] <[hidden email]>:
Hello Flavio,

just in case, about the equations, the Mahony's paper is here:
In particular the main result is in Theorem 4.1 .

I had the opportunity of discussing briefly with Mahony about this paper two years ago. If you have whatever question about the equations in the paper, 
feel free to ask :P.

On Mon, Dec 28, 2015 at 9:38 AM, flavio_just <[hidden email]> wrote:
Hey guys!
I am currently trying to reproduce the PPRZ C.F (ahrs_int_cmpl_euler.c) in
Matlab and for that I am trying to fully understand the equations and the
code itself. (Old version of PPRZ, I have no other choice =/)

I would like to know the following points, if it's possible:
- How the ahrs_align works and how lp_gyro, lp_accel and lp_mag are
calculated (is it the average of the sum of all the samples measured until
that moment?)

- Where is the gyro information of ahrs_propagate put together with accel
info to generate the so called C.F? I can notice ahrs_propagate integrates
the gyro and that ahrs_update_accel uses accel measurements, but where is
the line of code that puts all of them together for roll and pitch

- Why is it made a rotation from IMU to BODY always after ahrs_init,
propagates, etc? Can't it be used always the estimations in IMU and only
make the final rotation to BODY after all calculations?

- Finally, I assume that the functions go in this order: Init, Align,
Propagate, update_accel, update_mag. Is that correct? If yes, what is the
name of the variable containing the final att estimations that are uploaded
to the estimator and sent to telemetry?

I know I asked a lot of questions, but I really thank you for your help.
Best regards,

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Flávio Justino

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