Diff: Mahony/MahonyAHRS.cpp

Revision:

8:981f7e2365b6

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/Mahony/MahonyAHRS.cpp	Tue Jul 31 20:36:57 2018 +0000
@@ -0,0 +1,288 @@
+//=============================================================================================
+// MahonyAHRS.c
+//=============================================================================================
+//
+// Madgwick's implementation of Mayhony's AHRS algorithm.
+// See: http://www.x-io.co.uk/open-source-imu-and-ahrs-algorithms/
+//
+// From the x-io website "Open-source resources available on this website are
+// provided under the GNU General Public Licence unless an alternative licence
+// is provided in source."
+//
+// Date         Author          Notes
+// 29/09/2011   SOH Madgwick    Initial release
+// 02/10/2011   SOH Madgwick    Optimised for reduced CPU load
+//
+// Algorithm paper:
+// http://ieeexplore.ieee.org/xpl/login.jsp?tp=&arnumber=4608934&url=http%3A%2F%2Fieeexplore.ieee.org%2Fstamp%2Fstamp.jsp%3Ftp%3D%26arnumber%3D4608934
+//
+//=============================================================================================
+
+//-------------------------------------------------------------------------------------------
+// Header files
+
+#include "MahonyAHRS.h"
+#include <math.h>
+
+//-------------------------------------------------------------------------------------------
+// Definitions
+
+#define DEFAULT_SAMPLE_FREQ 1500.0f  // sample frequency in Hz
+#define twoKpDef    (2.0f * 0.5f)   // 2 * proportional gain
+#define twoKiDef    (2.0f * 0.1f)   // 2 * integral gain
+
+
+//============================================================================================
+// Functions
+
+//-------------------------------------------------------------------------------------------
+// AHRS algorithm update
+
+Mahony::Mahony()
+{
+    twoKp = twoKpDef;   // 2 * proportional gain (Kp)
+    twoKi = twoKiDef;   // 2 * integral gain (Ki)
+    q0 = 1.0f;
+    q1 = 0.0f;
+    q2 = 0.0f;
+    q3 = 0.0f;
+    integralFBx = 0.0f;
+    integralFBy = 0.0f;
+    integralFBz = 0.0f;
+    anglesComputed = 0;
+    invSampleFreq = 1.0f / DEFAULT_SAMPLE_FREQ;
+}
+
+void Mahony::update(float gx, float gy, float gz, float ax, float ay, float az, float mx, float my, float mz)
+{
+    float recipNorm;
+    float q0q0, q0q1, q0q2, q0q3, q1q1, q1q2, q1q3, q2q2, q2q3, q3q3;
+    float hx, hy, bx, bz;
+    float halfvx, halfvy, halfvz, halfwx, halfwy, halfwz;
+    float halfex, halfey, halfez;
+    float qa, qb, qc;
+
+    // Use IMU algorithm if magnetometer measurement invalid
+    // (avoids NaN in magnetometer normalisation)
+    if((mx == 0.0f) && (my == 0.0f) && (mz == 0.0f)) {
+        updateIMU(gx, gy, gz, ax, ay, az);
+        return;
+    }
+
+    // Convert gyroscope degrees/sec to radians/sec
+    gx *= 0.0174533f;
+    gy *= 0.0174533f;
+    gz *= 0.0174533f;
+
+    // Compute feedback only if accelerometer measurement valid
+    // (avoids NaN in accelerometer normalisation)
+    if(!((ax == 0.0f) && (ay == 0.0f) && (az == 0.0f))) {
+
+        // Normalise accelerometer measurement
+        recipNorm = invSqrt(ax * ax + ay * ay + az * az);
+        ax *= recipNorm;
+        ay *= recipNorm;
+        az *= recipNorm;
+
+        // Normalise magnetometer measurement
+        recipNorm = invSqrt(mx * mx + my * my + mz * mz);
+        mx *= recipNorm;
+        my *= recipNorm;
+        mz *= recipNorm;
+
+        // Auxiliary variables to avoid repeated arithmetic
+        q0q0 = q0 * q0;
+        q0q1 = q0 * q1;
+        q0q2 = q0 * q2;
+        q0q3 = q0 * q3;
+        q1q1 = q1 * q1;
+        q1q2 = q1 * q2;
+        q1q3 = q1 * q3;
+        q2q2 = q2 * q2;
+        q2q3 = q2 * q3;
+        q3q3 = q3 * q3;
+
+        // Reference direction of Earth's magnetic field
+        hx = 2.0f * (mx * (0.5f - q2q2 - q3q3) + my * (q1q2 - q0q3) + mz * (q1q3 + q0q2));
+        hy = 2.0f * (mx * (q1q2 + q0q3) + my * (0.5f - q1q1 - q3q3) + mz * (q2q3 - q0q1));
+        bx = sqrtf(hx * hx + hy * hy);
+        bz = 2.0f * (mx * (q1q3 - q0q2) + my * (q2q3 + q0q1) + mz * (0.5f - q1q1 - q2q2));
+
+        // Estimated direction of gravity and magnetic field
+        halfvx = q1q3 - q0q2;
+        halfvy = q0q1 + q2q3;
+        halfvz = q0q0 - 0.5f + q3q3;
+        halfwx = bx * (0.5f - q2q2 - q3q3) + bz * (q1q3 - q0q2);
+        halfwy = bx * (q1q2 - q0q3) + bz * (q0q1 + q2q3);
+        halfwz = bx * (q0q2 + q1q3) + bz * (0.5f - q1q1 - q2q2);
+
+        // Error is sum of cross product between estimated direction
+        // and measured direction of field vectors
+        halfex = (ay * halfvz - az * halfvy) + (my * halfwz - mz * halfwy);
+        halfey = (az * halfvx - ax * halfvz) + (mz * halfwx - mx * halfwz);
+        halfez = (ax * halfvy - ay * halfvx) + (mx * halfwy - my * halfwx);
+
+        // Compute and apply integral feedback if enabled
+        if(twoKi > 0.0f) {
+            // integral error scaled by Ki
+            integralFBx += twoKi * halfex * invSampleFreq;
+            integralFBy += twoKi * halfey * invSampleFreq;
+            integralFBz += twoKi * halfez * invSampleFreq;
+            gx += integralFBx;  // apply integral feedback
+            gy += integralFBy;
+            gz += integralFBz;
+        } else {
+            integralFBx = 0.0f; // prevent integral windup
+            integralFBy = 0.0f;
+            integralFBz = 0.0f;
+        }
+
+        // Apply proportional feedback
+        gx += twoKp * halfex;
+        gy += twoKp * halfey;
+        gz += twoKp * halfez;
+    }
+
+    // Integrate rate of change of quaternion
+    gx *= (0.5f * invSampleFreq);       // pre-multiply common factors
+    gy *= (0.5f * invSampleFreq);
+    gz *= (0.5f * invSampleFreq);
+    qa = q0;
+    qb = q1;
+    qc = q2;
+    q0 += (-qb * gx - qc * gy - q3 * gz);
+    q1 += (qa * gx + qc * gz - q3 * gy);
+    q2 += (qa * gy - qb * gz + q3 * gx);
+    q3 += (qa * gz + qb * gy - qc * gx);
+
+    // Normalise quaternion
+    recipNorm = invSqrt(q0 * q0 + q1 * q1 + q2 * q2 + q3 * q3);
+    q0 *= recipNorm;
+    q1 *= recipNorm;
+    q2 *= recipNorm;
+    q3 *= recipNorm;
+    anglesComputed = 0;
+}
+
+//-------------------------------------------------------------------------------------------
+// IMU algorithm update
+
+void Mahony::updateIMU(float gx, float gy, float gz, float ax, float ay, float az)
+{
+    float recipNorm;
+    float halfvx, halfvy, halfvz;
+    float halfex, halfey, halfez;
+    float qa, qb, qc;
+
+    // Convert gyroscope degrees/sec to radians/sec
+    gx *= 0.0174533f;
+    gy *= 0.0174533f;
+    gz *= 0.0174533f;
+
+    // Compute feedback only if accelerometer measurement valid
+    // (avoids NaN in accelerometer normalisation)
+    if(!((ax == 0.0f) && (ay == 0.0f) && (az == 0.0f))) {
+
+        // Normalise accelerometer measurement
+        recipNorm = invSqrt(ax * ax + ay * ay + az * az);
+        ax *= recipNorm;
+        ay *= recipNorm;
+        az *= recipNorm;
+
+        // Estimated direction of gravity
+        halfvx = q1 * q3 - q0 * q2;
+        halfvy = q0 * q1 + q2 * q3;
+        halfvz = q0 * q0 - 0.5f + q3 * q3;
+
+        // Error is sum of cross product between estimated
+        // and measured direction of gravity
+        halfex = (ay * halfvz - az * halfvy);
+        halfey = (az * halfvx - ax * halfvz);
+        halfez = (ax * halfvy - ay * halfvx);
+
+        // Compute and apply integral feedback if enabled
+        if(twoKi > 0.0f) {
+            // integral error scaled by Ki
+            integralFBx += twoKi * halfex * invSampleFreq;
+            integralFBy += twoKi * halfey * invSampleFreq;
+            integralFBz += twoKi * halfez * invSampleFreq;
+            gx += integralFBx;  // apply integral feedback
+            gy += integralFBy;
+            gz += integralFBz;
+        } else {
+            integralFBx = 0.0f; // prevent integral windup
+            integralFBy = 0.0f;
+            integralFBz = 0.0f;
+        }
+
+        // Apply proportional feedback
+        gx += twoKp * halfex;
+        gy += twoKp * halfey;
+        gz += twoKp * halfez;
+    }
+
+    // Integrate rate of change of quaternion
+    gx *= (0.5f * invSampleFreq);       // pre-multiply common factors
+    gy *= (0.5f * invSampleFreq);
+    gz *= (0.5f * invSampleFreq);
+    qa = q0;
+    qb = q1;
+    qc = q2;
+    q0 += (-qb * gx - qc * gy - q3 * gz);
+    q1 += (qa * gx + qc * gz - q3 * gy);
+    q2 += (qa * gy - qb * gz + q3 * gx);
+    q3 += (qa * gz + qb * gy - qc * gx);
+
+    // Normalise quaternion
+    recipNorm = invSqrt(q0 * q0 + q1 * q1 + q2 * q2 + q3 * q3);
+    q0 *= recipNorm;
+    q1 *= recipNorm;
+    q2 *= recipNorm;
+    q3 *= recipNorm;
+    anglesComputed = 0;
+}
+
+//-------------------------------------------------------------------------------------------
+// Fast inverse square-root
+// See: http://en.wikipedia.org/wiki/Fast_inverse_square_root
+/*
+float Mahony::invSqrt(float x)
+{
+    float halfx = 0.5f * x;
+    float y = x;
+    long i = *(long*)&y;
+    i = 0x5f3759df - (i>>1);
+    y = *(float*)&i;
+    y = y * (1.5f - (halfx * y * y));
+    y = y * (1.5f - (halfx * y * y));
+    return y;
+}
+*/
+/*
+float Mahony::invSqrt(float x){
+   unsigned int i = 0x5F1F1412 - (*(unsigned int*)&x >> 1);
+   float tmp = *(float*)&i;
+   return tmp * (1.69000231f - 0.714158168f * x * tmp * tmp);
+}
+*/
+
+float Mahony::invSqrt(float x)
+{
+    float temp = 1/(sqrt(x));
+    return temp;
+}
+
+//-------------------------------------------------------------------------------------------
+
+void Mahony::computeAngles()
+{
+    roll = atan2f(q0*q1 + q2*q3, 0.5f - q1*q1 - q2*q2);
+    pitch = asinf(-2.0f * (q1*q3 - q0*q2));
+    yaw = atan2f(q1*q2 + q0*q3, 0.5f - q2*q2 - q3*q3);
+    anglesComputed = 1;
+}
+
+
+//============================================================================================
+// END OF CODE
+//============================================================================================
\ No newline at end of file