2010-10-30 13:17:16 -03:00
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/*
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2012-03-11 04:59:53 -03:00
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APM_AHRS_DCM.cpp
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2010-10-24 15:37:10 -03:00
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2012-03-11 04:59:53 -03:00
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AHRS system using DCM matrices
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2011-06-12 20:49:01 -03:00
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2012-03-11 04:59:53 -03:00
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Based on DCM code by Doug Weibel, Jordi Mu<EFBFBD>oz and Jose Julio. DIYDrones.com
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2010-10-30 13:17:16 -03:00
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2012-03-11 04:59:53 -03:00
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Adapted for the general ArduPilot AHRS interface by Andrew Tridgell
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2010-10-30 13:17:16 -03:00
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2012-03-11 04:59:53 -03:00
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This library is free software; you can redistribute it and/or
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modify it under the terms of the GNU Lesser General Public License
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as published by the Free Software Foundation; either version 2.1
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of the License, or (at your option) any later version.
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2010-10-30 13:17:16 -03:00
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*/
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2012-03-11 04:59:53 -03:00
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#include <FastSerial.h>
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#include <AP_AHRS.h>
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2010-10-24 15:37:10 -03:00
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2012-02-24 20:30:59 -04:00
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// this is the speed in cm/s above which we first get a yaw lock with
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// the GPS
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#define GPS_SPEED_MIN 300
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2010-10-24 15:37:10 -03:00
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2012-02-24 20:30:59 -04:00
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// this is the speed in cm/s at which we stop using drift correction
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// from the GPS and wait for the ground speed to get above GPS_SPEED_MIN
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#define GPS_SPEED_RESET 100
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2010-10-24 15:37:10 -03:00
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2012-04-16 07:51:46 -03:00
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// table of user settable parameters
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const AP_Param::GroupInfo AP_AHRS::var_info[] PROGMEM = {
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2012-04-25 14:00:42 -03:00
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// @Param: YAW_P
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// @DisplayName: Yaw P
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// @Description: This controls the weight the compass has on the overall heading
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// @Range: 0 .4
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// @Increment: .01
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2012-04-16 07:51:46 -03:00
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AP_GROUPINFO("YAW_P", 0, AP_AHRS_DCM, _kp_yaw),
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AP_GROUPEND
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};
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2012-03-07 00:09:17 -04:00
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// run a full DCM update round
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2010-10-24 15:37:10 -03:00
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void
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2012-03-11 04:59:53 -03:00
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AP_AHRS_DCM::update(void)
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2010-10-24 15:37:10 -03:00
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{
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2011-09-15 00:04:08 -03:00
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float delta_t;
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2012-03-07 00:09:17 -04:00
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// tell the IMU to grab some data
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2010-12-30 03:52:35 -04:00
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_imu->update();
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2011-06-12 20:49:01 -03:00
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2012-03-07 00:09:17 -04:00
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// ask the IMU how much time this sensor reading represents
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2011-09-15 00:04:08 -03:00
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delta_t = _imu->get_delta_time();
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2012-03-07 00:09:17 -04:00
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// Get current values for gyros
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_gyro_vector = _imu->get_gyro();
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2012-03-11 04:59:53 -03:00
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_accel_vector = _imu->get_accel();
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2011-09-11 15:03:55 -03:00
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2012-03-07 00:09:17 -04:00
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// Integrate the DCM matrix using gyro inputs
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matrix_update(delta_t);
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2011-09-11 15:03:55 -03:00
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2012-03-07 00:09:17 -04:00
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// Normalize the DCM matrix
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normalize();
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2011-09-11 15:03:55 -03:00
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2012-03-11 04:59:53 -03:00
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// Perform drift correction
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drift_correction(delta_t);
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2010-10-24 15:37:10 -03:00
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2012-03-07 00:09:17 -04:00
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// paranoid check for bad values in the DCM matrix
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check_matrix();
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2010-11-14 22:15:16 -04:00
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2012-03-07 00:09:17 -04:00
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// Calculate pitch, roll, yaw for stabilization and navigation
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euler_angles();
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2010-11-17 17:20:20 -04:00
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}
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2011-06-12 20:49:01 -03:00
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2012-03-07 00:09:17 -04:00
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// update the DCM matrix using only the gyros
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2011-06-12 20:49:01 -03:00
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void
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2012-03-11 04:59:53 -03:00
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AP_AHRS_DCM::matrix_update(float _G_Dt)
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2010-10-24 15:37:10 -03:00
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{
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2012-03-23 02:22:56 -03:00
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// _omega_integ_corr is used for centripetal correction
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2012-03-07 02:12:42 -04:00
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// (theoretically better than _omega)
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2012-03-07 00:09:17 -04:00
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_omega_integ_corr = _gyro_vector + _omega_I;
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2012-03-07 02:12:42 -04:00
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2012-03-07 00:09:17 -04:00
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// Equation 16, adding proportional and integral correction terms
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2012-03-31 09:21:00 -03:00
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_omega = _omega_integ_corr + _omega_P;
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2012-03-07 00:09:17 -04:00
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2012-03-19 03:24:15 -03:00
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// this is a replacement of the DCM matrix multiply (equation
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2012-03-07 02:12:42 -04:00
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// 17), with known zero elements removed and the matrix
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// operations inlined. This runs much faster than the original
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// version of this code, as the compiler was doing a terrible
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// job of realising that so many of the factors were in common
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// or zero. It also uses much less stack, as we no longer need
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2012-03-19 03:24:15 -03:00
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// two additional local matrices
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Vector3f r = _omega * _G_Dt;
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_dcm_matrix.rotate(r);
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2010-10-24 15:37:10 -03:00
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}
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2011-12-13 06:32:50 -04:00
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/*
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reset the DCM matrix and omega. Used on ground start, and on
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extreme errors in the matrix
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*/
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void
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2012-03-11 04:59:53 -03:00
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AP_AHRS_DCM::reset(bool recover_eulers)
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2011-12-13 06:32:50 -04:00
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{
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2012-01-13 00:48:07 -04:00
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if (_compass != NULL) {
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2012-03-11 01:30:49 -04:00
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_compass->null_offsets_disable();
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2012-01-13 00:48:07 -04:00
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}
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2012-02-23 07:58:41 -04:00
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// reset the integration terms
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2012-03-08 03:12:46 -04:00
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_omega_I.zero();
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_omega_P.zero();
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_omega_integ_corr.zero();
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_omega.zero();
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2012-02-22 16:59:16 -04:00
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2012-02-23 07:58:41 -04:00
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// if the caller wants us to try to recover to the current
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// attitude then calculate the dcm matrix from the current
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// roll/pitch/yaw values
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if (recover_eulers && !isnan(roll) && !isnan(pitch) && !isnan(yaw)) {
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2012-03-10 02:07:07 -04:00
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_dcm_matrix.from_euler(roll, pitch, yaw);
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2012-02-23 07:58:41 -04:00
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} else {
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// otherwise make it flat
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2012-03-10 02:07:07 -04:00
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_dcm_matrix.from_euler(0, 0, 0);
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2012-02-23 07:58:41 -04:00
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}
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2012-01-13 00:48:07 -04:00
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if (_compass != NULL) {
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_compass->null_offsets_enable(); // This call is needed to restart the nulling
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// Otherwise the reset in the DCM matrix can mess up
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// the nulling
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}
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2011-12-13 06:32:50 -04:00
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}
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2010-10-24 15:37:10 -03:00
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2012-02-22 17:00:25 -04:00
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/*
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check the DCM matrix for pathological values
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*/
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void
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2012-03-11 04:59:53 -03:00
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AP_AHRS_DCM::check_matrix(void)
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2012-02-22 17:00:25 -04:00
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{
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2012-02-23 07:58:41 -04:00
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if (_dcm_matrix.is_nan()) {
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//Serial.printf("ERROR: DCM matrix NAN\n");
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SITL_debug("ERROR: DCM matrix NAN\n");
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renorm_blowup_count++;
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2012-03-11 04:59:53 -03:00
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reset(true);
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2012-02-23 07:58:41 -04:00
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return;
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}
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2012-02-22 17:00:25 -04:00
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// some DCM matrix values can lead to an out of range error in
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// the pitch calculation via asin(). These NaN values can
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// feed back into the rest of the DCM matrix via the
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// error_course value.
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2012-02-22 20:38:51 -04:00
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if (!(_dcm_matrix.c.x < 1.0 &&
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_dcm_matrix.c.x > -1.0)) {
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2012-02-22 17:00:25 -04:00
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// We have an invalid matrix. Force a normalisation.
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renorm_range_count++;
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normalize();
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2012-02-23 07:58:41 -04:00
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2012-02-23 19:45:47 -04:00
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if (_dcm_matrix.is_nan() ||
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2012-02-23 07:58:41 -04:00
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fabs(_dcm_matrix.c.x) > 10) {
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2012-02-22 17:00:25 -04:00
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// normalisation didn't fix the problem! We're
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// in real trouble. All we can do is reset
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2012-02-23 07:58:41 -04:00
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//Serial.printf("ERROR: DCM matrix error. _dcm_matrix.c.x=%f\n",
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// _dcm_matrix.c.x);
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2012-02-22 17:00:25 -04:00
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SITL_debug("ERROR: DCM matrix error. _dcm_matrix.c.x=%f\n",
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_dcm_matrix.c.x);
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renorm_blowup_count++;
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2012-03-11 04:59:53 -03:00
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reset(true);
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2012-02-22 17:00:25 -04:00
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}
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}
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}
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2012-03-07 02:12:42 -04:00
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// renormalise one vector component of the DCM matrix
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// this will return false if renormalization fails
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2012-03-07 00:09:17 -04:00
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bool
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2012-03-11 04:59:53 -03:00
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AP_AHRS_DCM::renorm(Vector3f const &a, Vector3f &result)
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2010-10-24 15:37:10 -03:00
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{
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2011-06-15 09:24:51 -03:00
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float renorm_val;
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2012-02-17 01:15:27 -04:00
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// numerical errors will slowly build up over time in DCM,
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// causing inaccuracies. We can keep ahead of those errors
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// using the renormalization technique from the DCM IMU paper
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// (see equations 18 to 21).
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// For APM we don't bother with the taylor expansion
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// optimisation from the paper as on our 2560 CPU the cost of
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// the sqrt() is 44 microseconds, and the small time saving of
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// the taylor expansion is not worth the potential of
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// additional error buildup.
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// Note that we can get significant renormalisation values
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// when we have a larger delta_t due to a glitch eleswhere in
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// APM, such as a I2c timeout or a set of EEPROM writes. While
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// we would like to avoid these if possible, if it does happen
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// we don't want to compound the error by making DCM less
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// accurate.
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2012-03-07 00:09:17 -04:00
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renorm_val = 1.0 / a.length();
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2012-02-17 01:15:27 -04:00
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2012-03-01 00:22:39 -04:00
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// keep the average for reporting
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_renorm_val_sum += renorm_val;
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_renorm_val_count++;
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2012-02-22 20:38:51 -04:00
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if (!(renorm_val < 2.0 && renorm_val > 0.5)) {
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2012-02-17 01:15:27 -04:00
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// this is larger than it should get - log it as a warning
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renorm_range_count++;
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2012-02-22 20:38:51 -04:00
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if (!(renorm_val < 1.0e6 && renorm_val > 1.0e-6)) {
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2012-02-17 01:15:27 -04:00
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// we are getting values which are way out of
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// range, we will reset the matrix and hope we
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// can recover our attitude using drift
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// correction before we hit the ground!
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2012-02-23 07:58:41 -04:00
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//Serial.printf("ERROR: DCM renormalisation error. renorm_val=%f\n",
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// renorm_val);
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2012-02-17 01:15:27 -04:00
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SITL_debug("ERROR: DCM renormalisation error. renorm_val=%f\n",
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renorm_val);
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renorm_blowup_count++;
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2012-03-07 00:09:17 -04:00
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return false;
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2012-02-17 01:15:27 -04:00
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}
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2010-10-24 15:37:10 -03:00
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}
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2012-03-07 00:09:17 -04:00
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result = a * renorm_val;
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return true;
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}
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/*************************************************
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Direction Cosine Matrix IMU: Theory
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William Premerlani and Paul Bizard
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Numerical errors will gradually reduce the orthogonality conditions expressed by equation 5
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to approximations rather than identities. In effect, the axes in the two frames of reference no
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longer describe a rigid body. Fortunately, numerical error accumulates very slowly, so it is a
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simple matter to stay ahead of it.
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We call the process of enforcing the orthogonality conditions <EFBFBD>renormalization<EFBFBD>.
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*/
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void
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2012-03-11 04:59:53 -03:00
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AP_AHRS_DCM::normalize(void)
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2012-03-07 00:09:17 -04:00
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{
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float error;
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Vector3f t0, t1, t2;
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error = _dcm_matrix.a * _dcm_matrix.b; // eq.18
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t0 = _dcm_matrix.a - (_dcm_matrix.b * (0.5f * error)); // eq.19
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t1 = _dcm_matrix.b - (_dcm_matrix.a * (0.5f * error)); // eq.19
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t2 = t0 % t1; // c= a x b // eq.20
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if (!renorm(t0, _dcm_matrix.a) ||
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!renorm(t1, _dcm_matrix.b) ||
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!renorm(t2, _dcm_matrix.c)) {
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// Our solution is blowing up and we will force back
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// to last euler angles
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2012-03-11 04:59:53 -03:00
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reset(true);
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2012-03-07 00:09:17 -04:00
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}
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2010-10-24 15:37:10 -03:00
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}
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2012-03-07 00:09:17 -04:00
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2012-03-31 09:21:00 -03:00
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// yaw drift correction using the compass
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2011-06-12 20:49:01 -03:00
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void
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2012-03-31 09:21:00 -03:00
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AP_AHRS_DCM::drift_correction_compass(float deltat)
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2010-10-24 15:37:10 -03:00
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{
|
2012-03-31 09:21:00 -03:00
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if (_compass == NULL ||
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_compass->last_update == _compass_last_update) {
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// slowly degrade the yaw error term so we cope
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// gracefully with the compass going offline
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_drift_error_earth.z *= 0.97;
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return;
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2012-03-07 00:09:17 -04:00
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}
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2011-06-12 20:49:01 -03:00
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2012-03-31 09:21:00 -03:00
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Vector3f mag = Vector3f(_compass->mag_x, _compass->mag_y, _compass->mag_z);
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2012-03-08 03:12:46 -04:00
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2012-03-31 09:21:00 -03:00
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if (!_have_initial_yaw) {
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// this is our first estimate of the yaw,
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// or the compass has come back online after
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// no readings for 2 seconds.
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//
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// construct a DCM matrix based on the current
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// roll/pitch and the compass heading.
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2012-04-15 23:14:19 -03:00
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2012-03-31 09:21:00 -03:00
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// First ensure the compass heading has been
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// calculated
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_compass->calculate(_dcm_matrix);
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2012-04-15 23:14:19 -03:00
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2012-03-31 09:21:00 -03:00
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// now construct a new DCM matrix
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_compass->null_offsets_disable();
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_dcm_matrix.from_euler(roll, pitch, _compass->heading);
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_compass->null_offsets_enable();
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_have_initial_yaw = true;
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_field_strength = mag.length();
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_compass_last_update = _compass->last_update;
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2012-03-23 02:22:56 -03:00
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return;
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}
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2012-03-31 09:21:00 -03:00
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float yaw_deltat = 1.0e-6*(_compass->last_update - _compass_last_update);
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2012-03-23 02:22:56 -03:00
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2012-03-31 09:21:00 -03:00
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_compass_last_update = _compass->last_update;
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2012-03-23 02:22:56 -03:00
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2012-03-31 09:21:00 -03:00
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// keep a estimate of the magnetic field strength
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_field_strength = (_field_strength * 0.95) + (mag.length() * 0.05);
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2012-03-23 02:22:56 -03:00
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2012-03-31 09:21:00 -03:00
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// get the mag vector in the earth frame
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Vector3f rb = _dcm_matrix * mag;
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2012-03-23 02:22:56 -03:00
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2012-03-31 09:21:00 -03:00
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// normalise rb so that it can be directly combined with
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// rotations given by the accelerometers, which are in 1g units
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rb *= yaw_deltat / _field_strength;
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2012-03-23 02:22:56 -03:00
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2012-03-31 09:21:00 -03:00
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if (rb.is_inf()) {
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// not a valid vector
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return;
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}
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2012-03-23 02:22:56 -03:00
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2012-03-31 09:21:00 -03:00
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// get the earths magnetic field (only X and Y components needed)
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Vector3f mag_earth = Vector3f(cos(_compass->get_declination()),
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sin(_compass->get_declination()), 0);
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2012-03-23 02:22:56 -03:00
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2012-03-31 09:21:00 -03:00
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// calculate the error term in earth frame
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Vector3f error = rb % mag_earth;
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2012-03-23 02:22:56 -03:00
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2012-03-31 09:21:00 -03:00
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// setup the z component of the total drift error in earth
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// frame. This is then used by the main drift correction code
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2012-06-16 18:44:31 -03:00
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_drift_error_earth.z = error.z*70; //constrain(error.z, -0.4, 0.4);
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//TODO: figure out proper error scaling instead of using 70
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2012-03-23 02:22:56 -03:00
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2012-03-31 09:21:00 -03:00
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_error_yaw_sum += fabs(_drift_error_earth.z);
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_error_yaw_count++;
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2012-03-23 02:22:56 -03:00
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}
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// perform drift correction. This function aims to update _omega_P and
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// _omega_I with our best estimate of the short term and long term
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// gyro error. The _omega_P value is what pulls our attitude solution
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// back towards the reference vector quickly. The _omega_I term is an
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// attempt to learn the long term drift rate of the gyros.
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//
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// This drift correction implementation is based on a paper
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// by Bill Premerlani from here:
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// http://gentlenav.googlecode.com/files/RollPitchDriftCompensation.pdf
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void
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AP_AHRS_DCM::drift_correction(float deltat)
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{
|
2012-06-16 18:44:31 -03:00
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Vector3f error;
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Vector3f gps_velocity;
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bool nogps=false;
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uint32_t last_correction_time;
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if(_omega.length() < ToRad(20))
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_omega_I += _omega_I_delta * deltat;
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// perform yaw drift correction if we have a new yaw reference
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// vector
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drift_correction_compass(deltat);
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// scale the accel vector so it is in 1g units. This brings it
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// into line with the mag vector, allowing the two to be combined
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_accel_vector *= (deltat / _gravity);
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// integrate the accel vector in the earth frame between GPS readings
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_ra_sum += _dcm_matrix * _accel_vector;
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// keep a sum of the deltat values, so we know how much time
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// we have integrated over
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_ra_deltat += deltat;
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if (_gps == NULL || _gps->status() != GPS::GPS_OK) {
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// no GPS, or no lock. We assume zero velocity. This at
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// least means we can cope with gyro drift while sitting
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// on a bench with no GPS lock
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if (_ra_deltat < 0.1) {
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// not enough time has accumulated
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return;
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}
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nogps=true;
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gps_velocity.zero();
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last_correction_time = millis();
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} else {
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if (_gps->last_fix_time == _ra_sum_start) {
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// we don't have a new GPS fix - nothing more to do
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return;
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}
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gps_velocity = Vector3f(_gps->velocity_north(), _gps->velocity_east(), 0);
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last_correction_time = _gps->last_fix_time;
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}
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// see if this is our first time through - in which case we
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// just setup the start times and return
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if (_ra_sum_start == 0) {
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_ra_sum_start = last_correction_time;
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_gps_last_velocity = gps_velocity;
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return;
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}
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// get the corrected acceleration vector in earth frame. Units
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// are 1g
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Vector3f ge;
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if(!nogps) {
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ge = Vector3f(0, 0, -1.0) + ((gps_velocity - _gps_last_velocity)/_gravity)/_ra_deltat;
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}
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else {
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ge = Vector3f(0, 0, -1.0);
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}
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// calculate the error term in earth frame
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error = (_ra_sum/_ra_deltat % ge)/ge.length();
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// extract the X and Y components for the total drift
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// error. The Z component comes from the yaw source
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// we constrain the error on each axis to 0.2
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// the Z component of this error comes from the yaw correction
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_drift_error_earth.x = error.x; //constrain(error.x, -0.2, 0.2);
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_drift_error_earth.y = error.y;// constrain(error.y, -0.2, 0.2);
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//_drift_error_earth.z = error.z;
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// convert the error term to body frame
|
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error = _dcm_matrix.mul_transpose(_drift_error_earth);
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|
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// we now want to calculate _omega_P and _omega_I. The
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// _omega_P value is what drags us quickly to the
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// accelerometer reading.
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_omega_P = error * _kp;
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_omega_I_delta = (error * _ki) / _ra_deltat;
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// the _omega_I is the long term accumulated gyro
|
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// error. This determines how much gyro drift we can
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// handle.
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//_omega_I_delta_sum += error * _ki * _ra_deltat;
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//_omega_I_sum_time += _ra_deltat;
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// if we have accumulated a gyro drift estimate for 15
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// seconds, then move it to the _omega_I term which is applied
|
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// on each update
|
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/*if (_omega_I_sum_time > 5) {
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// limit the slope of omega_I on each axis to
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// the maximum drift rate reported by the sensor driver
|
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//float drift_limit = _gyro_drift_limit * _ra_deltat * 2;
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_omega_I_delta_sum /= _omega_I_sum_time;
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_omega_I_delta_sum.x =_omega_I_delta_sum.x; //constrain(_omega_I_delta_sum.x, -drift_limit, drift_limit);
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_omega_I_delta_sum.y =_omega_I_delta_sum.y; //constrain(_omega_I_delta_sum.y, -drift_limit, drift_limit);
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_omega_I_delta_sum.z =_omega_I_delta_sum.z; //constrain(_omega_I_delta_sum.z, -drift_limit, drift_limit);
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_omega_I_delta = _omega_I_delta_sum;
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_omega_I_delta_sum.zero();
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_omega_I_sum_time = 0;
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}*/
|
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// zero our accumulator ready for the next GPS step
|
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_ra_sum.zero();
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_ra_deltat = 0;
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_ra_sum_start = last_correction_time;
|
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// remember the GPS velocity for next time
|
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_gps_last_velocity = gps_velocity;
|
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|
// these sums support the reporting of the DCM state via MAVLink
|
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_error_rp_sum += Vector3f(_drift_error_earth.x, _drift_error_earth.y, 0).length();
|
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_error_rp_count++;
|
2012-03-23 02:22:56 -03:00
|
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}
|
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|
2010-10-24 15:37:10 -03:00
|
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|
2012-03-07 02:12:42 -04:00
|
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// calculate the euler angles which will be used for high level
|
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|
// navigation control
|
2011-06-12 20:49:01 -03:00
|
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|
void
|
2012-03-11 04:59:53 -03:00
|
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|
AP_AHRS_DCM::euler_angles(void)
|
2010-10-24 15:37:10 -03:00
|
|
|
|
{
|
2012-03-10 02:07:07 -04:00
|
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_dcm_matrix.to_euler(&roll, &pitch, &yaw);
|
2011-06-12 20:49:01 -03:00
|
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|
|
2010-12-01 03:58:04 -04:00
|
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roll_sensor = degrees(roll) * 100;
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pitch_sensor = degrees(pitch) * 100;
|
2012-02-23 07:58:41 -04:00
|
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yaw_sensor = degrees(yaw) * 100;
|
2010-10-24 15:37:10 -03:00
|
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|
|
|
2010-12-01 03:58:04 -04:00
|
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|
|
if (yaw_sensor < 0)
|
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|
|
|
yaw_sensor += 36000;
|
2010-10-24 15:37:10 -03:00
|
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|
|
}
|
|
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|
2012-03-01 00:22:39 -04:00
|
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|
|
/* reporting of DCM state for MAVLink */
|
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|
// average error_roll_pitch since last call
|
2012-03-11 04:59:53 -03:00
|
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|
|
float AP_AHRS_DCM::get_error_rp(void)
|
2012-03-01 00:22:39 -04:00
|
|
|
|
{
|
|
|
|
|
if (_error_rp_count == 0) {
|
2012-03-28 18:57:53 -03:00
|
|
|
|
// this happens when telemetry is setup on two
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|
|
// serial ports
|
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|
|
return _error_rp_last;
|
2012-03-01 00:22:39 -04:00
|
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|
|
}
|
2012-03-28 18:57:53 -03:00
|
|
|
|
_error_rp_last = _error_rp_sum / _error_rp_count;
|
2012-03-01 00:22:39 -04:00
|
|
|
|
_error_rp_sum = 0;
|
|
|
|
|
_error_rp_count = 0;
|
2012-03-28 18:57:53 -03:00
|
|
|
|
return _error_rp_last;
|
2012-03-01 00:22:39 -04:00
|
|
|
|
}
|
|
|
|
|
|
|
|
|
|
// average error_yaw since last call
|
2012-03-11 04:59:53 -03:00
|
|
|
|
float AP_AHRS_DCM::get_error_yaw(void)
|
2012-03-01 00:22:39 -04:00
|
|
|
|
{
|
|
|
|
|
if (_error_yaw_count == 0) {
|
2012-03-28 18:57:53 -03:00
|
|
|
|
// this happens when telemetry is setup on two
|
|
|
|
|
// serial ports
|
|
|
|
|
return _error_yaw_last;
|
2012-03-01 00:22:39 -04:00
|
|
|
|
}
|
2012-03-28 18:57:53 -03:00
|
|
|
|
_error_yaw_last = _error_yaw_sum / _error_yaw_count;
|
2012-03-01 00:22:39 -04:00
|
|
|
|
_error_yaw_sum = 0;
|
|
|
|
|
_error_yaw_count = 0;
|
2012-03-28 18:57:53 -03:00
|
|
|
|
return _error_yaw_last;
|
2012-03-01 00:22:39 -04:00
|
|
|
|
}
|