代碼路徑ardupolit/modules/PX4Firmware/src/modules/attitude_estimator_so3/attitude_estimator_so3_main.cpp
最近結合慣性導航這本書,詳細看了四元數姿态解算的代碼,然後對這部分代碼進行了詳細的分析,分享給大家,如果分析有誤請大家留言不吝賜教!!
- void AHRS_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)) {
- MahonyAHRSupdateIMU(gx, gy, gz, ax, ay, az);
- return;
- }
- // Compute feedback only if accelerometer measurement valid (avoids NaN in accelerometer normalisation)
- if(!((ax == 0.0f) && (ay == 0.0f) && (az == 0.0f))) {
- recipNorm = invSqrt(ax * ax + ay * ay + az * az);
- ax *= recipNorm;
- ay *= recipNorm;
- az *= recipNorm;
- recipNorm = invSqrt(mx * mx + my * my + mz * mz);
- mx *= recipNorm;
- my *= recipNorm;
- mz *= recipNorm;
- 現在我們假設CbR旋轉矩陣是經過加速度計校正後的矩陣,當某個确定的向量(機體系中)經過這個矩陣旋轉之後(到地理坐标系),這兩個坐标系在XOY平面上重合,隻是在z軸旋轉上會存在一個偏航角的誤差。下圖表示的是經過CbR旋轉之後的機體坐标系b和地理坐标系n的相對關系。可以明顯發現加速度計可以把機體坐标系b通過四元數法從任意角度拉到與地理坐标系n水準的位置上,這時,隻剩下一個偏航角誤差。這也是為什麼加速度計誤差修正偏航的原因。 hx,hy,hz是地理坐标系下的磁傳感器值,可以有機體坐标系下的mx,my,mz左乘CbR得到,假設理想情況下的機體能夠和當地的地理坐标系處于同一XOY平面,且機頭指北,那麼此時的磁傳感器值應該為bx,0,bz,此時我們很友善的可以得到bx²=hx²+hy²,bz=hz,當時理想必定是理想,飛機的姿态不可能達到這種狀态,是以我們再根據bx,0,bz(地理坐标系)右乘CbR得到估計後的磁傳感器值halfwx,halfwy,halfwz(這部分解說間黃色底色部分)
- 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 = sqrt(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);
- 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) {
- integralFBx += twoKi * halfex * (1.0f / sampleFreq); // integral error scaled by Ki
- integralFBy += twoKi * halfey * (1.0f / sampleFreq);
- integralFBz += twoKi * halfez * (1.0f / sampleFreq);
- 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 * (1.0f / sampleFreq)); // pre-multiply common factors
- gy *= (0.5f * (1.0f / sampleFreq));
- gz *= (0.5f * (1.0f / sampleFreq));
- 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;
- }