/****************************************************************************
*
* 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
* COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
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* BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
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*
****************************************************************************/
/**
* @file accelerometer_calibration.cpp
*
* 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
*
* ===== Rotation =====
*
* Calibrating using model:
* accel_corr = accel_T_r * (rot * accel_raw - accel_offs_r)
*
* Actual correction:
* accel_corr = rot * accel_T * (accel_raw - accel_offs)
*
* Known: accel_T_r, accel_offs_r, rot
* Unknown: accel_T, accel_offs
*
* Solution:
* accel_T_r * (rot * accel_raw - accel_offs_r) = rot * accel_T * (accel_raw - accel_offs)
* rot^-1 * accel_T_r * (rot * accel_raw - accel_offs_r) = accel_T * (accel_raw - accel_offs)
* rot^-1 * accel_T_r * rot * accel_raw - rot^-1 * accel_T_r * accel_offs_r = accel_T * accel_raw - accel_T * accel_offs)
* => accel_T = rot^-1 * accel_T_r * rot
* => accel_offs = rot^-1 * accel_offs_r
*
* @author Anton Babushkin <anton.babushkin@me.com>
*/
#include "accelerometer_calibration.h"
#include "commander_helper.h"
#include <unistd.h>
#include <stdio.h>
#include <poll.h>
#include <fcntl.h>
#include <sys/prctl.h>
#include <math.h>
#include <mathlib/mathlib.h>
#include <string.h>
#include <drivers/drv_hrt.h>
#include <uORB/topics/sensor_combined.h>
#include <drivers/drv_accel.h>
#include <geo/geo.h>
#include <conversion/rotation.h>
#include <systemlib/param/param.h>
#include <systemlib/err.h>
#include <mavlink/mavlink_log.h>
/* oddly, ERROR is not defined for c++ */
#ifdef ERROR
# undef ERROR
#endif
static const int ERROR = -1;
int do_accel_calibration_measurements(int mavlink_fd, float accel_offs[3], float accel_T[3][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);
int do_accel_calibration(int mavlink_fd)
{
mavlink_log_info(mavlink_fd, "accel calibration: started");
mavlink_log_info(mavlink_fd, "accel calibration: progress <0>");
struct accel_scale accel_scale = {
0.0f,
1.0f,
0.0f,
1.0f,
0.0f,
1.0f,
};
int res = OK;
/* reset all offsets to zero and all scales to one */
int fd = open(ACCEL_DEVICE_PATH, 0);
res = ioctl(fd, ACCELIOCSSCALE, (long unsigned int)&accel_scale);
close(fd);
if (res != OK) {
mavlink_log_critical(mavlink_fd, "ERROR: failed to reset scale / offsets");
}
/* measure and calculate offsets & scales */
float accel_offs[3];
float accel_T[3][3];
res = do_accel_calibration_measurements(mavlink_fd, accel_offs, accel_T);
if (res == OK) {
/* measurements completed successfully, rotate calibration values */
param_t board_rotation_h = param_find("SENS_BOARD_ROT");
int32_t board_rotation_int;
param_get(board_rotation_h, &(board_rotation_int));
enum Rotation board_rotation_id = (enum Rotation)board_rotation_int;
math::Matrix board_rotation(3, 3);
get_rot_matrix(board_rotation_id, &board_rotation);
math::Matrix board_rotation_t = board_rotation.transpose();
math::Vector3 accel_offs_vec;
accel_offs_vec.set(&accel_offs[0]);
math::Vector3 accel_offs_rotated = board_rotation_t * accel_offs_vec;
math::Matrix accel_T_mat(3, 3);
accel_T_mat.set(&accel_T[0][0]);
math::Matrix accel_T_rotated = board_rotation_t * accel_T_mat * board_rotation;
accel_scale.x_offset = accel_offs_rotated(0);
accel_scale.x_scale = accel_T_rotated(0, 0);
accel_scale.y_offset = accel_offs_rotated(1);
accel_scale.y_scale = accel_T_rotated(1, 1);
accel_scale.z_offset = accel_offs_rotated(2);
accel_scale.z_scale = accel_T_rotated(2, 2);
/* set parameters */
if (param_set(param_find("SENS_ACC_XOFF"), &(accel_scale.x_offset))
|| param_set(param_find("SENS_ACC_YOFF"), &(accel_scale.y_offset))
|| param_set(param_find("SENS_ACC_ZOFF"), &(accel_scale.z_offset))
|| param_set(param_find("SENS_ACC_XSCALE"), &(accel_scale.x_scale))
|| param_set(param_find("SENS_ACC_YSCALE"), &(accel_scale.y_scale))
|| param_set(param_find("SENS_ACC_ZSCALE"), &(accel_scale.z_scale))) {
mavlink_log_critical(mavlink_fd, "ERROR: setting accel params failed");
res = ERROR;
}
}
if (res == OK) {
/* apply new scaling and offsets */
int fd = open(ACCEL_DEVICE_PATH, 0);
res = ioctl(fd, ACCELIOCSSCALE, (long unsigned int)&accel_scale);
close(fd);
if (res != OK) {
mavlink_log_critical(mavlink_fd, "ERROR: failed to apply new params for accel");
}
}
if (res == OK) {
/* auto-save to EEPROM */
res = param_save_default();
if (res != OK) {
mavlink_log_critical(mavlink_fd, "ERROR: failed to save parameters");
}
}
if (res == OK) {
mavlink_log_info(mavlink_fd, "accel calibration: done");
} else {
mavlink_log_info(mavlink_fd, "accel calibration: failed");
}
return res;
}
int do_accel_calibration_measurements(int mavlink_fd, float accel_offs[3], float accel_T[3][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-" };
int sensor_combined_sub = orb_subscribe(ORB_ID(sensor_combined));
unsigned done_count = 0;
int res = OK;
while (true) {
bool done = true;
unsigned old_done_count = done_count;
done_count = 0;
for (int i = 0; i < 6; i++) {
if (!data_collected[i]) {
done = false;
}
}
if (old_done_count != done_count)
mavlink_log_info(mavlink_fd, "accel calibration: progress <%u>", 17 * done_count);
if (done)
break;
mavlink_log_info(mavlink_fd, "directions left: %s%s%s%s%s%s",
(!data_collected[0]) ? "x+ " : "",
(!data_collected[1]) ? "x- " : "",
(!data_collected[2]) ? "y+ " : "",
(!data_collected[3]) ? "y- " : "",
(!data_collected[4]) ? "z+ " : "",
(!data_collected[5]) ? "z- " : "");
int orient = detect_orientation(mavlink_fd, sensor_combined_sub);
if (orient < 0) {
res = ERROR;
break;
}
if (data_collected[orient]) {
mavlink_log_info(mavlink_fd, "%s done, please rotate to a different axis", orientation_strs[orient]);
continue;
}
mavlink_log_info(mavlink_fd, "accel measurement started: %s axis", orientation_strs[orient]);
read_accelerometer_avg(sensor_combined_sub, &(accel_ref[orient][0]), samples_num);
mavlink_log_info(mavlink_fd, "result for %s axis: [ %.2f %.2f %.2f ]", orientation_strs[orient],
(double)accel_ref[orient][0],
(double)accel_ref[orient][1],
(double)accel_ref[orient][2]);
data_collected[orient] = true;
tune_neutral();
}
close(sensor_combined_sub);
if (res == OK) {
/* calculate offsets and transform matrix */
res = calculate_calibration_values(accel_ref, accel_T, accel_offs, CONSTANTS_ONE_G);
if (res != OK) {
mavlink_log_info(mavlink_fd, "ERROR: calibration values calculation error");
}
}
return res;
}
/*
* 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 = 0.5f;
/* set "still" threshold to 0.25 m/s^2 */
float still_thr2 = pow(0.25f, 2);
/* set accel error threshold to 5m/s^2 */
float accel_err_thr = 5.0f;
/* still time required in us */
hrt_abstime still_time = 2000000;
struct pollfd fds[1];
fds[0].fd = sub_sensor_combined;
fds[0].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;
unsigned poll_errcount = 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++) {
float d = sensor.accelerometer_m_s2[i] - accel_ema[i];
accel_ema[i] += d * w;
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, "detected rest position, waiting...");
t_still = t;
t_timeout = t + timeout;
} else {
/* still since t_still */
if (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, "detected motion, please hold still...");
t_still = 0;
}
}
} else if (poll_ret == 0) {
poll_errcount++;
}
if (t > t_timeout) {
poll_errcount++;
}
if (poll_errcount > 1000) {
mavlink_log_critical(mavlink_fd, "ERROR: failed reading sensor");
return ERROR;
}
}
if (fabsf(accel_ema[0] - CONSTANTS_ONE_G) < accel_err_thr &&
fabsf(accel_ema[1]) < accel_err_thr &&
fabsf(accel_ema[2]) < accel_err_thr)
return 0; // [ g, 0, 0 ]
if (fabsf(accel_ema[0] + CONSTANTS_ONE_G) < accel_err_thr &&
fabsf(accel_ema[1]) < accel_err_thr &&
fabsf(accel_ema[2]) < accel_err_thr)
return 1; // [ -g, 0, 0 ]
if (fabsf(accel_ema[0]) < accel_err_thr &&
fabsf(accel_ema[1] - CONSTANTS_ONE_G) < accel_err_thr &&
fabsf(accel_ema[2]) < accel_err_thr)
return 2; // [ 0, g, 0 ]
if (fabsf(accel_ema[0]) < accel_err_thr &&
fabsf(accel_ema[1] + CONSTANTS_ONE_G) < accel_err_thr &&
fabsf(accel_ema[2]) < accel_err_thr)
return 3; // [ 0, -g, 0 ]
if (fabsf(accel_ema[0]) < accel_err_thr &&
fabsf(accel_ema[1]) < accel_err_thr &&
fabsf(accel_ema[2] - CONSTANTS_ONE_G) < accel_err_thr)
return 4; // [ 0, 0, g ]
if (fabsf(accel_ema[0]) < accel_err_thr &&
fabsf(accel_ema[1]) < accel_err_thr &&
fabsf(accel_ema[2] + CONSTANTS_ONE_G) < accel_err_thr)
return 5; // [ 0, 0, -g ]
mavlink_log_critical(mavlink_fd, "ERROR: invalid orientation");
return ERROR; // 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];
fds[0].fd = sensor_combined_sub;
fds[0].events = POLLIN;
int count = 0;
float accel_sum[3] = { 0.0f, 0.0f, 0.0f };
int errcount = 0;
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 {
errcount++;
continue;
}
if (errcount > samples_num / 10)
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 == 0.0f)
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;
}