px4_autopilot/EKF/utils.hpp

#include <matrix/math.hpp>

#pragma once

// return the square of two floating point numbers - used in auto coded sections
static constexpr float sq(float var) { return var * var; }

// converts Tait-Bryan 312 sequence of rotations from frame 1 to frame 2
// to the corresponding rotation matrix that rotates from frame 2 to frame 1
// rot312(0) - First rotation is a RH rotation about the Z axis (rad)
// rot312(1) - Second rotation is a RH rotation about the X axis (rad)
// rot312(2) - Third rotation is a RH rotation about the Y axis (rad)
// See http://www.atacolorado.com/eulersequences.doc
matrix::Dcmf taitBryan312ToRotMat(const matrix::Vector3f &rot312);

// Use Kahan summation algorithm to get the sum of "sum_previous" and "input".
// This function relies on the caller to be responsible for keeping a copy of
// "accumulator" and passing this value at the next iteration.
// Ref: https://en.wikipedia.org/wiki/Kahan_summation_algorithm
float kahanSummation(float sum_previous, float input, float &accumulator);

// calculate the inverse rotation matrix from a quaternion rotation
// this produces the inverse rotation to that produced by the math library quaternion to Dcmf operator
matrix::Dcmf quatToInverseRotMat(const matrix::Quatf &quat);

// We should use a 3-2-1 Tait-Bryan (yaw-pitch-roll) rotation sequence
// when there is more roll than pitch tilt and a 3-1-2 rotation sequence
// when there is more pitch than roll tilt to avoid gimbal lock.
bool shouldUse321RotationSequence(const matrix::Dcmf& R);

float getEuler321Yaw(const matrix::Quatf& q);
float getEuler321Yaw(const matrix::Dcmf& R);

float getEuler312Yaw(const matrix::Quatf& q);
float getEuler312Yaw(const matrix::Dcmf& R);

matrix::Dcmf updateEuler321YawInRotMat(float yaw, const matrix::Dcmf& rot_in);
matrix::Dcmf updateEuler312YawInRotMat(float yaw, const matrix::Dcmf& rot_in);

// Checks which euler rotation sequence to use and update yaw in rotation matrix
matrix::Dcmf updateYawInRotMat(float yaw, const matrix::Dcmf& rot_in);

namespace ecl{
	inline float powf(float x, int exp)
	{
		float ret;
		if (exp > 0) {
			ret = x;
			for (int count = 1; count < exp; count++) {
				ret *= x;
			}
			return ret;
		} else if (exp < 0) {
			return 1.0f / ecl::powf(x, -exp);
		}
		return 1.0f;
	}
}