117 lines
3.5 KiB
C++
117 lines
3.5 KiB
C++
/**
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* @file Mechanization_bRn.cpp
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* @date Jan 25, 2012
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* @author Chris Beall
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* @author Frank Dellaert
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*/
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#include "Mechanization_bRn2.h"
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#include <boost/foreach.hpp>
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namespace gtsam {
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/* ************************************************************************* */
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Mechanization_bRn2 Mechanization_bRn2::initializeVector(const std::list<Vector>& U,
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const std::list<Vector>& F, const double g_e, bool flat) {
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Matrix Umat = (Matrix(3, U.size()) << concatVectors(U)).finished();
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Matrix Fmat = (Matrix(3, F.size()) << concatVectors(F)).finished();
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return initialize(Umat, Fmat, g_e, flat);
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}
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/* ************************************************************************* */
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Mechanization_bRn2 Mechanization_bRn2::initialize(const Matrix& U,
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const Matrix& F, const double g_e, bool flat) {
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// estimate gyro bias by averaging gyroscope readings (10.62)
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Vector3 x_g = U.rowwise().mean();
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Vector3 meanF = F.rowwise().mean();
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// estimate gravity
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Vector3 b_g;
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if(g_e == 0) {
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if (flat)
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// acceleration measured is along the z-axis.
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b_g = (Vector3(3) << 0.0, 0.0, norm_2(meanF)).finished();
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else
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// acceleration measured is the opposite of gravity (10.13)
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b_g = -meanF;
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} else {
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if (flat)
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// gravity is downward along the z-axis since we are flat on the ground
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b_g = (Vector3(3) << 0.0,0.0,g_e).finished();
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else
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// normalize b_g and attribute remainder to biases
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b_g = - g_e * meanF/meanF.norm();
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}
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// estimate accelerometer bias
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Vector3 x_a = meanF + b_g;
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// initialize roll, pitch (eqns. 10.14, 10.15)
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double g1=b_g(0);
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double g2=b_g(1);
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double g3=b_g(2);
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// Farrell08book eqn. 10.14
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double roll = atan2(g2, g3);
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// Farrell08book eqn. 10.15
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double pitch = atan2(-g1, sqrt(g2 * g2 + g3 * g3));
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double yaw = 0;
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// This returns body-to-nav nRb
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Rot3 bRn = Rot3::Ypr(yaw, pitch, roll).inverse();
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return Mechanization_bRn2(bRn, x_g, x_a);
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}
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/* ************************************************************************* */
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Mechanization_bRn2 Mechanization_bRn2::correct(const Vector3& dx) const {
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Vector3 rho = sub(dx, 0, 3);
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Rot3 delta_nRn = Rot3::Rodrigues(rho);
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Rot3 bRn = bRn_ * delta_nRn;
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Vector3 x_g = x_g_ + sub(dx, 3, 6);
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Vector3 x_a = x_a_ + sub(dx, 6, 9);
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return Mechanization_bRn2(bRn, x_g, x_a);
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}
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/* ************************************************************************* */
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Mechanization_bRn2 Mechanization_bRn2::integrate(const Vector3& u,
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const double dt) const {
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// integrate rotation nRb based on gyro measurement u and bias x_g
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#ifndef MODEL_NAV_FRAME_ROTATION
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// get body to inertial (measured in b) from gyro, subtract bias
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Vector3 b_omega_ib = u - x_g_;
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// nav to inertial due to Earth's rotation and our movement on Earth surface
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// TODO: figure out how to do this if we need it
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Vector3 b_omega_in; b_omega_in.setZero();
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// calculate angular velocity on bRn measured in body frame
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Vector3 b_omega_bn = b_omega_in - b_omega_ib;
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#else
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// Assume a non-rotating nav frame (probably an approximation)
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// calculate angular velocity on bRn measured in body frame
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Vector3 b_omega_bn = x_g_ - u;
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#endif
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// convert to navigation frame
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Rot3 nRb = bRn_.inverse();
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Vector3 n_omega_bn = nRb * b_omega_bn;
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// integrate bRn using exponential map, assuming constant over dt
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Rot3 delta_nRn = Rot3::Rodrigues(n_omega_bn*dt);
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Rot3 bRn = bRn_.compose(delta_nRn);
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// implicit updating of biases (variables just do not change)
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// x_g = x_g;
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// x_a = x_a;
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return Mechanization_bRn2(bRn, x_g_, x_a_);
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}
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} /* namespace gtsam */
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