/****************************************************************************
*
* Copyright (C) 2013 PX4 Development Team. All rights reserved.
* Author: Anton Babushkin <anton.babushkin@me.com>
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
*
* 1. Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in
* the documentation and/or other materials provided with the
* distribution.
* 3. Neither the name PX4 nor the names of its contributors may be
* used to endorse or promote products derived from this software
* without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
* "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
* LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
* FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
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****************************************************************************/
/**
* @file accelerometer_calibration.c
*
* Implementation of accelerometer calibration.
*
* Transform acceleration vector to true orientation, scale and offset
*
* ===== Model =====
* accel_corr = accel_T * (accel_raw - accel_offs)
*
* accel_corr[3] - fully corrected acceleration vector in body frame
* accel_T[3][3] - accelerometers transform matrix, rotation and scaling transform
* accel_raw[3] - raw acceleration vector
* accel_offs[3] - acceleration offset vector
*
* ===== Calibration =====
*
* Reference vectors
* accel_corr_ref[6][3] = [ g 0 0 ] // nose up
* | -g 0 0 | // nose down
* | 0 g 0 | // left side down
* | 0 -g 0 | // right side down
* | 0 0 g | // on back
* [ 0 0 -g ] // level
* accel_raw_ref[6][3]
*
* accel_corr_ref[i] = accel_T * (accel_raw_ref[i] - accel_offs), i = 0...5
*
* 6 reference vectors * 3 axes = 18 equations
* 9 (accel_T) + 3 (accel_offs) = 12 unknown constants
*
* Find accel_offs
*
* accel_offs[i] = (accel_raw_ref[i*2][i] + accel_raw_ref[i*2+1][i]) / 2
*
* Find accel_T
*
* 9 unknown constants
* need 9 equations -> use 3 of 6 measurements -> 3 * 3 = 9 equations
*
* accel_corr_ref[i*2] = accel_T * (accel_raw_ref[i*2] - accel_offs), i = 0...2
*
* Solve separate system for each row of accel_T:
*
* accel_corr_ref[j*2][i] = accel_T[i] * (accel_raw_ref[j*2] - accel_offs), j = 0...2
*
* A * x = b
*
* x = [ accel_T[0][i] ]
* | accel_T[1][i] |
* [ accel_T[2][i] ]
*
* b = [ accel_corr_ref[0][i] ] // One measurement per axis is enough
* | accel_corr_ref[2][i] |
* [ accel_corr_ref[4][i] ]
*
* a[i][j] = accel_raw_ref[i][j] - accel_offs[j], i = 0;2;4, j = 0...2
*
* Matrix A is common for all three systems:
* A = [ a[0][0] a[0][1] a[0][2] ]
* | a[2][0] a[2][1] a[2][2] |
* [ a[4][0] a[4][1] a[4][2] ]
*
* x = A^-1 * b
*
* accel_T = A^-1 * g
* g = 9.80665
*
* @author Anton Babushkin <anton.babushkin@me.com>
*/
#include "accelerometer_calibration.h"
#include <poll.h>
#include <drivers/drv_hrt.h>
#include <uORB/topics/sensor_combined.h>
#include <drivers/drv_accel.h>
#include <systemlib/conversions.h>
#include <mavlink/mavlink_log.h>
void do_accel_calibration(int status_pub, struct vehicle_status_s *status, int mavlink_fd);
int do_accel_calibration_mesurements(int mavlink_fd, float accel_offs[3], float accel_scale[3]);
int detect_orientation(int mavlink_fd, int sub_sensor_combined);
int read_accelerometer_avg(int sensor_combined_sub, float accel_avg[3], int samples_num);
int mat_invert3(float src[3][3], float dst[3][3]);
int calculate_calibration_values(float accel_ref[6][3], float accel_T[3][3], float accel_offs[3], float g);
void do_accel_calibration(int status_pub, struct vehicle_status_s *status, int mavlink_fd) {
/* announce change */
mavlink_log_info(mavlink_fd, "accel calibration started");
/* set to accel calibration mode */
status->flag_preflight_accel_calibration = true;
state_machine_publish(status_pub, status, mavlink_fd);
/* measure and calculate offsets & scales */
float accel_offs[3];
float accel_scale[3];
int res = do_accel_calibration_mesurements(mavlink_fd, accel_offs, accel_scale);
if (res == OK) {
/* measurements complete successfully, set parameters */
if (param_set(param_find("SENS_ACC_XOFF"), &(accel_offs[0]))
|| param_set(param_find("SENS_ACC_YOFF"), &(accel_offs[1]))
|| param_set(param_find("SENS_ACC_ZOFF"), &(accel_offs[2]))
|| param_set(param_find("SENS_ACC_XSCALE"), &(accel_scale[0]))
|| param_set(param_find("SENS_ACC_YSCALE"), &(accel_scale[1]))
|| param_set(param_find("SENS_ACC_ZSCALE"), &(accel_scale[2]))) {
mavlink_log_critical(mavlink_fd, "ERROR: setting offs or scale failed");
}
int fd = open(ACCEL_DEVICE_PATH, 0);
struct accel_scale ascale = {
accel_offs[0],
accel_scale[0],
accel_offs[1],
accel_scale[1],
accel_offs[2],
accel_scale[2],
};
if (OK != ioctl(fd, ACCELIOCSSCALE, (long unsigned int)&ascale))
warn("WARNING: failed to set scale / offsets for accel");
close(fd);
/* auto-save to EEPROM */
int save_ret = param_save_default();
if (save_ret != 0) {
warn("WARNING: auto-save of params to storage failed");
}
mavlink_log_info(mavlink_fd, "accel calibration done");
tune_confirm();
sleep(2);
tune_confirm();
sleep(2);
/* third beep by cal end routine */
} else {
/* measurements error */
mavlink_log_info(mavlink_fd, "accel calibration aborted");
tune_error();
sleep(2);
}
/* exit accel calibration mode */
status->flag_preflight_accel_calibration = false;
state_machine_publish(status_pub, status, mavlink_fd);
}
int do_accel_calibration_mesurements(int mavlink_fd, float accel_offs[3], float accel_scale[3]) {
const int samples_num = 2500;
float accel_ref[6][3];
bool data_collected[6] = { false, false, false, false, false, false };
const char *orientation_strs[6] = { "x+", "x-", "y+", "y-", "z+", "z-" };
/* reset existing calibration */
int fd = open(ACCEL_DEVICE_PATH, 0);
struct accel_scale ascale_null = {
0.0f,
1.0f,
0.0f,
1.0f,
0.0f,
1.0f,
};
int ioctl_res = ioctl(fd, ACCELIOCSSCALE, (long unsigned int)&ascale_null);
close(fd);
if (OK != ioctl_res) {
warn("ERROR: failed to set scale / offsets for accel");
return ERROR;
}
int sensor_combined_sub = orb_subscribe(ORB_ID(sensor_combined));
while (true) {
bool done = true;
char str[80];
int str_ptr;
str_ptr = sprintf(str, "keep vehicle still:");
for (int i = 0; i < 6; i++) {
if (!data_collected[i]) {
str_ptr += sprintf(&(str[str_ptr]), " %s", orientation_strs[i]);
done = false;
}
}
if (done)
break;
mavlink_log_info(mavlink_fd, str);
int orient = detect_orientation(mavlink_fd, sensor_combined_sub);
if (orient < 0)
return ERROR;
sprintf(str, "meas started: %s", orientation_strs[orient]);
mavlink_log_info(mavlink_fd, str);
read_accelerometer_avg(sensor_combined_sub, &(accel_ref[orient][0]), samples_num);
str_ptr = sprintf(str, "meas result for %s: [ %.2f %.2f %.2f ]", orientation_strs[orient], accel_ref[orient][0], accel_ref[orient][1], accel_ref[orient][2]);
mavlink_log_info(mavlink_fd, str);
data_collected[orient] = true;
tune_confirm();
}
close(sensor_combined_sub);
/* calculate offsets and rotation+scale matrix */
float accel_T[3][3];
int res = calculate_calibration_values(accel_ref, accel_T, accel_offs, CONSTANTS_ONE_G);
if (res != 0) {
mavlink_log_info(mavlink_fd, "ERROR: calibration values calc error");
return ERROR;
}
/* convert accel transform matrix to scales,
* rotation part of transform matrix is not used by now
*/
for (int i = 0; i < 3; i++) {
accel_scale[i] = accel_T[i][i];
}
return OK;
}
/*
* Wait for vehicle become still and detect it's orientation.
*
* @return 0..5 according to orientation when vehicle is still and ready for measurements,
* ERROR if vehicle is not still after 30s or orientation error is more than 5m/s^2
*/
int detect_orientation(int mavlink_fd, int sub_sensor_combined) {
struct sensor_combined_s sensor;
/* exponential moving average of accel */
float accel_ema[3] = { 0.0f, 0.0f, 0.0f };
/* max-hold dispersion of accel */
float accel_disp[3] = { 0.0f, 0.0f, 0.0f };
/* EMA time constant in seconds*/
float ema_len = 0.2f;
/* set "still" threshold to 0.1 m/s^2 */
float still_thr2 = pow(0.1f, 2);
/* set accel error threshold to 5m/s^2 */
float accel_err_thr = 5.0f;
/* still time required in us */
int64_t still_time = 2000000;
struct pollfd fds[1] = { { .fd = sub_sensor_combined, .events = POLLIN } };
hrt_abstime t_start = hrt_absolute_time();
/* set timeout to 30s */
hrt_abstime timeout = 30000000;
hrt_abstime t_timeout = t_start + timeout;
hrt_abstime t = t_start;
hrt_abstime t_prev = t_start;
hrt_abstime t_still = 0;
while (true) {
/* wait blocking for new data */
int poll_ret = poll(fds, 1, 1000);
if (poll_ret) {
orb_copy(ORB_ID(sensor_combined), sub_sensor_combined, &sensor);
t = hrt_absolute_time();
float dt = (t - t_prev) / 1000000.0f;
t_prev = t;
float w = dt / ema_len;
for (int i = 0; i < 3; i++) {
accel_ema[i] = accel_ema[i] * (1.0f - w) + sensor.accelerometer_m_s2[i] * w;
float d = (float) sensor.accelerometer_m_s2[i] - accel_ema[i];
d = d * d;
accel_disp[i] = accel_disp[i] * (1.0f - w);
if (d > accel_disp[i])
accel_disp[i] = d;
}
/* still detector with hysteresis */
if ( accel_disp[0] < still_thr2 &&
accel_disp[1] < still_thr2 &&
accel_disp[2] < still_thr2 ) {
/* is still now */
if (t_still == 0) {
/* first time */
mavlink_log_info(mavlink_fd, "still...");
t_still = t;
t_timeout = t + timeout;
} else {
/* still since t_still */
if ((int64_t) t - (int64_t) t_still > still_time) {
/* vehicle is still, exit from the loop to detection of its orientation */
break;
}
}
} else if ( accel_disp[0] > still_thr2 * 2.0f ||
accel_disp[1] > still_thr2 * 2.0f ||
accel_disp[2] > still_thr2 * 2.0f) {
/* not still, reset still start time */
if (t_still != 0) {
mavlink_log_info(mavlink_fd, "moving...");
t_still = 0;
}
}
} else if (poll_ret == 0) {
/* any poll failure for 1s is a reason to abort */
mavlink_log_info(mavlink_fd, "ERROR: poll failure");
return -3;
}
if (t > t_timeout) {
mavlink_log_info(mavlink_fd, "ERROR: timeout");
return -1;
}
}
if ( fabs(accel_ema[0] - CONSTANTS_ONE_G) < accel_err_thr &&
fabs(accel_ema[1]) < accel_err_thr &&
fabs(accel_ema[2]) < accel_err_thr )
return 0; // [ g, 0, 0 ]
if ( fabs(accel_ema[0] + CONSTANTS_ONE_G) < accel_err_thr &&
fabs(accel_ema[1]) < accel_err_thr &&
fabs(accel_ema[2]) < accel_err_thr )
return 1; // [ -g, 0, 0 ]
if ( fabs(accel_ema[0]) < accel_err_thr &&
fabs(accel_ema[1] - CONSTANTS_ONE_G) < accel_err_thr &&
fabs(accel_ema[2]) < accel_err_thr )
return 2; // [ 0, g, 0 ]
if ( fabs(accel_ema[0]) < accel_err_thr &&
fabs(accel_ema[1] + CONSTANTS_ONE_G) < accel_err_thr &&
fabs(accel_ema[2]) < accel_err_thr )
return 3; // [ 0, -g, 0 ]
if ( fabs(accel_ema[0]) < accel_err_thr &&
fabs(accel_ema[1]) < accel_err_thr &&
fabs(accel_ema[2] - CONSTANTS_ONE_G) < accel_err_thr )
return 4; // [ 0, 0, g ]
if ( fabs(accel_ema[0]) < accel_err_thr &&
fabs(accel_ema[1]) < accel_err_thr &&
fabs(accel_ema[2] + CONSTANTS_ONE_G) < accel_err_thr )
return 5; // [ 0, 0, -g ]
mavlink_log_info(mavlink_fd, "ERROR: invalid orientation");
return -2; // Can't detect orientation
}
/*
* Read specified number of accelerometer samples, calculate average and dispersion.
*/
int read_accelerometer_avg(int sensor_combined_sub, float accel_avg[3], int samples_num) {
struct pollfd fds[1] = { { .fd = sensor_combined_sub, .events = POLLIN } };
int count = 0;
float accel_sum[3] = { 0.0f, 0.0f, 0.0f };
while (count < samples_num) {
int poll_ret = poll(fds, 1, 1000);
if (poll_ret == 1) {
struct sensor_combined_s sensor;
orb_copy(ORB_ID(sensor_combined), sensor_combined_sub, &sensor);
for (int i = 0; i < 3; i++)
accel_sum[i] += sensor.accelerometer_m_s2[i];
count++;
} else {
return ERROR;
}
}
for (int i = 0; i < 3; i++) {
accel_avg[i] = accel_sum[i] / count;
}
return OK;
}
int mat_invert3(float src[3][3], float dst[3][3]) {
float det = src[0][0] * (src[1][1] * src[2][2] - src[1][2] * src[2][1]) -
src[0][1] * (src[1][0] * src[2][2] - src[1][2] * src[2][0]) +
src[0][2] * (src[1][0] * src[2][1] - src[1][1] * src[2][0]);
if (det == 0.0)
return ERROR; // Singular matrix
dst[0][0] = (src[1][1] * src[2][2] - src[1][2] * src[2][1]) / det;
dst[1][0] = (src[1][2] * src[2][0] - src[1][0] * src[2][2]) / det;
dst[2][0] = (src[1][0] * src[2][1] - src[1][1] * src[2][0]) / det;
dst[0][1] = (src[0][2] * src[2][1] - src[0][1] * src[2][2]) / det;
dst[1][1] = (src[0][0] * src[2][2] - src[0][2] * src[2][0]) / det;
dst[2][1] = (src[0][1] * src[2][0] - src[0][0] * src[2][1]) / det;
dst[0][2] = (src[0][1] * src[1][2] - src[0][2] * src[1][1]) / det;
dst[1][2] = (src[0][2] * src[1][0] - src[0][0] * src[1][2]) / det;
dst[2][2] = (src[0][0] * src[1][1] - src[0][1] * src[1][0]) / det;
return OK;
}
int calculate_calibration_values(float accel_ref[6][3], float accel_T[3][3], float accel_offs[3], float g) {
/* calculate offsets */
for (int i = 0; i < 3; i++) {
accel_offs[i] = (accel_ref[i * 2][i] + accel_ref[i * 2 + 1][i]) / 2;
}
/* fill matrix A for linear equations system*/
float mat_A[3][3];
memset(mat_A, 0, sizeof(mat_A));
for (int i = 0; i < 3; i++) {
for (int j = 0; j < 3; j++) {
float a = accel_ref[i * 2][j] - accel_offs[j];
mat_A[i][j] = a;
}
}
/* calculate inverse matrix for A */
float mat_A_inv[3][3];
if (mat_invert3(mat_A, mat_A_inv) != OK)
return ERROR;
/* copy results to accel_T */
for (int i = 0; i < 3; i++) {
for (int j = 0; j < 3; j++) {
/* simplify matrices mult because b has only one non-zero element == g at index i */
accel_T[j][i] = mat_A_inv[j][i] * g;
}
}
return OK;
}