Diff: IMUfilter.cpp
- Revision:
- 0:6a5296aa7dbf
- Child:
- 1:4b0e8441f099
diff -r 000000000000 -r 6a5296aa7dbf IMUfilter.cpp
--- /dev/null Thu Jan 01 00:00:00 1970 +0000
+++ b/IMUfilter.cpp Sat Feb 05 18:57:55 2011 +0000
@@ -0,0 +1,228 @@
+/**
+ * @author Aaron Berk
+ *
+ * @section LICENSE
+ *
+ * Copyright (c) 2010 ARM Limited
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ *
+ * @section DESCRIPTION
+ *
+ * IMU orientation filter developed by Sebastian Madgwick.
+ *
+ * Find more details about his paper here:
+ *
+ * http://code.google.com/p/imumargalgorithm30042010sohm/
+ */
+
+/**
+ * Includes
+ */
+#include "IMUfilter.h"
+
+IMUfilter::IMUfilter(double rate, double gyroscopeMeasurementError){
+
+ firstUpdate = 0;
+
+ //Quaternion orientation of earth frame relative to auxiliary frame.
+ AEq_1 = 1;
+ AEq_2 = 0;
+ AEq_3 = 0;
+ AEq_4 = 0;
+
+ //Estimated orientation quaternion elements with initial conditions.
+ SEq_1 = 1;
+ SEq_2 = 0;
+ SEq_3 = 0;
+ SEq_4 = 0;
+
+ //Sampling period (typical value is ~0.1s).
+ deltat = rate;
+
+ //Gyroscope measurement error (in degrees per second).
+ gyroMeasError = gyroscopeMeasurementError;
+
+ //Compute beta.
+ beta = sqrt(3.0 / 4.0) * (PI * (gyroMeasError / 180.0));
+
+}
+
+void IMUfilter::updateFilter(double w_x, double w_y, double w_z, double a_x, double a_y, double a_z) {
+
+ //Local system variables.
+
+ //Vector norm.
+ double norm;
+ //Quaternion rate from gyroscope elements.
+ double SEqDot_omega_1;
+ double SEqDot_omega_2;
+ double SEqDot_omega_3;
+ double SEqDot_omega_4;
+ //Objective function elements.
+ double f_1;
+ double f_2;
+ double f_3;
+ //Objective function Jacobian elements.
+ double J_11or24;
+ double J_12or23;
+ double J_13or22;
+ double J_14or21;
+ double J_32;
+ double J_33;
+ //Objective function gradient elements.
+ double nablaf_1;
+ double nablaf_2;
+ double nablaf_3;
+ double nablaf_4;
+
+ //Auxiliary variables to avoid reapeated calculations.
+ double halfSEq_1 = 0.5 * SEq_1;
+ double halfSEq_2 = 0.5 * SEq_2;
+ double halfSEq_3 = 0.5 * SEq_3;
+ double halfSEq_4 = 0.5 * SEq_4;
+ double twoSEq_1 = 2.0 * SEq_1;
+ double twoSEq_2 = 2.0 * SEq_2;
+ double twoSEq_3 = 2.0 * SEq_3;
+
+ //Compute the quaternion rate measured by gyroscopes.
+ SEqDot_omega_1 = -halfSEq_2 * w_x - halfSEq_3 * w_y - halfSEq_4 * w_z;
+ SEqDot_omega_2 = halfSEq_1 * w_x + halfSEq_3 * w_z - halfSEq_4 * w_y;
+ SEqDot_omega_3 = halfSEq_1 * w_y - halfSEq_2 * w_z + halfSEq_4 * w_x;
+ SEqDot_omega_4 = halfSEq_1 * w_z + halfSEq_2 * w_y - halfSEq_3 * w_x;
+
+ //Normalise the accelerometer measurement.
+ norm = sqrt(a_x * a_x + a_y * a_y + a_z * a_z);
+ a_x /= norm;
+ a_y /= norm;
+ a_z /= norm;
+
+ //Compute the objective function and Jacobian.
+ f_1 = twoSEq_2 * SEq_4 - twoSEq_1 * SEq_3 - a_x;
+ f_2 = twoSEq_1 * SEq_2 + twoSEq_3 * SEq_4 - a_y;
+ f_3 = 1.0 - twoSEq_2 * SEq_2 - twoSEq_3 * SEq_3 - a_z;
+ //J_11 negated in matrix multiplication.
+ J_11or24 = twoSEq_3;
+ J_12or23 = 2 * SEq_4;
+ //J_12 negated in matrix multiplication
+ J_13or22 = twoSEq_1;
+ J_14or21 = twoSEq_2;
+ //Negated in matrix multiplication.
+ J_32 = 2 * J_14or21;
+ //Negated in matrix multiplication.
+ J_33 = 2 * J_11or24;
+
+ //Compute the gradient (matrix multiplication).
+ nablaf_1 = J_14or21 * f_2 - J_11or24 * f_1;
+ nablaf_2 = J_12or23 * f_1 + J_13or22 * f_2 - J_32 * f_3;
+ nablaf_3 = J_12or23 * f_2 - J_33 * f_3 - J_13or22 * f_1;
+ nablaf_4 = J_14or21 * f_1 + J_11or24 * f_2;
+
+ //Normalise the gradient.
+ norm = sqrt(nablaf_1 * nablaf_1 + nablaf_2 * nablaf_2 + nablaf_3 * nablaf_3 + nablaf_4 * nablaf_4);
+ nablaf_1 /= norm;
+ nablaf_2 /= norm;
+ nablaf_3 /= norm;
+ nablaf_4 /= norm;
+
+ //Compute then integrate the estimated quaternion rate.
+ SEq_1 += (SEqDot_omega_1 - (beta * nablaf_1)) * deltat;
+ SEq_2 += (SEqDot_omega_2 - (beta * nablaf_2)) * deltat;
+ SEq_3 += (SEqDot_omega_3 - (beta * nablaf_3)) * deltat;
+ SEq_4 += (SEqDot_omega_4 - (beta * nablaf_4)) * deltat;
+
+ //Normalise quaternion
+ norm = sqrt(SEq_1 * SEq_1 + SEq_2 * SEq_2 + SEq_3 * SEq_3 + SEq_4 * SEq_4);
+ SEq_1 /= norm;
+ SEq_2 /= norm;
+ SEq_3 /= norm;
+ SEq_4 /= norm;
+
+ if (firstUpdate == 0) {
+ //Store orientation of auxiliary frame.
+ AEq_1 = SEq_1;
+ AEq_2 = SEq_2;
+ AEq_3 = SEq_3;
+ AEq_4 = SEq_4;
+ firstUpdate = 1;
+ }
+
+}
+
+void IMUfilter::computeEuler(void){
+
+ //Quaternion describing orientation of sensor relative to earth.
+ double ESq_1, ESq_2, ESq_3, ESq_4;
+ //Quaternion describing orientation of sensor relative to auxiliary frame.
+ double ASq_1, ASq_2, ASq_3, ASq_4;
+
+ //Compute the quaternion conjugate.
+ ESq_1 = SEq_1;
+ ESq_2 = -SEq_2;
+ ESq_3 = -SEq_3;
+ ESq_4 = -SEq_4;
+
+ //Compute the quaternion product.
+ ASq_1 = ESq_1 * AEq_1 - ESq_2 * AEq_2 - ESq_3 * AEq_3 - ESq_4 * AEq_4;
+ ASq_2 = ESq_1 * AEq_2 + ESq_2 * AEq_1 + ESq_3 * AEq_4 - ESq_4 * AEq_3;
+ ASq_3 = ESq_1 * AEq_3 - ESq_2 * AEq_4 + ESq_3 * AEq_1 + ESq_4 * AEq_2;
+ ASq_4 = ESq_1 * AEq_4 + ESq_2 * AEq_3 - ESq_3 * AEq_2 + ESq_4 * AEq_1;
+
+ //Compute the Euler angles from the quaternion.
+ phi = atan2(2 * ASq_3 * ASq_4 - 2 * ASq_1 * ASq_2, 2 * ASq_1 * ASq_1 + 2 * ASq_4 * ASq_4 - 1);
+ theta = asin(2 * ASq_2 * ASq_3 - 2 * ASq_1 * ASq_3);
+ psi = atan2(2 * ASq_2 * ASq_3 - 2 * ASq_1 * ASq_4, 2 * ASq_1 * ASq_1 + 2 * ASq_2 * ASq_2 - 1);
+
+}
+
+double IMUfilter::getRoll(void){
+
+ return phi;
+
+}
+
+double IMUfilter::getPitch(void){
+
+ return theta;
+
+}
+
+double IMUfilter::getYaw(void){
+
+ return psi;
+
+}
+
+void IMUfilter::reset(void) {
+
+ firstUpdate = 0;
+
+ //Quaternion orientation of earth frame relative to auxiliary frame.
+ AEq_1 = 1;
+ AEq_2 = 0;
+ AEq_3 = 0;
+ AEq_4 = 0;
+
+ //Estimated orientation quaternion elements with initial conditions.
+ SEq_1 = 1;
+ SEq_2 = 0;
+ SEq_3 = 0;
+ SEq_4 = 0;
+
+}
Ian Molesworth