discrete_ekf_no_north.c

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/*
 * Copyright (C) Mario Coppola
 *
 * This file is part of paparazzi
 *
 * paparazzi is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2, or (at your option)
 * any later version.
 *
 * paparazzi is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with paparazzi; see the file COPYING.  If not, see
 * <http://www.gnu.org/licenses/>.
 */
#include "modules/relative_localization_filter/discrete_ekf_no_north.h"
#include "math/pprz_algebra_float.h"
#include <math.h>
#include <stdio.h> // needed for the printf statements
 
enum ekf_statein {x12, y12, z1, z2, u1, v1, u2, v2, gam};
enum ekf_input {u1dm, v1dm, u2dm, v2dm, r1m, r2m};
 
void extractPhiGamma(float **inmat, float **phi, float **gamma, int m, int n_a, int n_b)
{
  int totalsize = m + n_b;
  for (int i = 0; i < m; i++) {
    for (int j = 0; j < totalsize; j++) {
      if (j < n_a) {
        phi[i][j] = inmat[i][j];
      } else {
        gamma[i][j - n_a] = inmat[i][j];
      }
    }
  }
}
 
/*
 * Creates a combined matrix o = [ a[m][n_a] b[m][n_b] ;
 *                                 0[m][n_a] 0[m][n_b] ]
 */
void float_mat_combine(float **a, float **b, float **o, int m, int n_a, int n_b)
{
  int totalsize = m + n_b;
  for (int i = 0; i < totalsize; i++) {
    for (int j = 0; j < totalsize; j++) {
      if (i < m && j < n_a) {
        o[i][j] = a[i][j];
      } else if (i < m) {
        o[i][j] = b[i][j - n_a];
      } else {
        o[i][j] = 0.0;
      }
    }
  }
}
 
/*
 * Continuous to discrete transition matrix
 */
void c2d(int m, int nA, int nB, float **Fx, float **G, float dt, float **phi, float **gamma)
{
 
  int totalsize = m + nB;
  float combmat[totalsize][totalsize];
  float expm[totalsize][totalsize];
 
  MAKE_MATRIX_PTR(_Fx, Fx, EKF_N);
  MAKE_MATRIX_PTR(_G, G, EKF_M);
  MAKE_MATRIX_PTR(_phi, phi, m);
  MAKE_MATRIX_PTR(_gamma, gamma, m);
  MAKE_MATRIX_PTR(_combmat, combmat, totalsize);
  MAKE_MATRIX_PTR(_expm, expm, totalsize);
 
  float_mat_scale(_Fx, dt, m, nA);
  float_mat_scale(_G,  dt, m, nB);
 
  float_mat_combine(_Fx, _G, _combmat, m, nA, nB);
  float_mat_exp(_combmat, _expm, totalsize);
  extractPhiGamma(_expm, _phi, _gamma, m, nA, nB);
}
 
/*
 * Continuous time state transition equation
 * state is: {x_rel,y_rel,h1,h2,u1,v1,u2,v2,gamma}
 */
 
void discrete_ekf_no_north_fsym(float *statein, float *input, float *output)
{
  output[0] =  input[r1m] * statein[y12] - statein[u1] + statein[u2] * cosf(statein[gam]) - statein[v2] * sinf(
                 statein[gam]);
  output[1] = -input[r1m] * statein[x12] - statein[v1] + statein[u2] * sinf(statein[gam]) + statein[v2] * cosf(
                statein[gam]);
  output[2] = 0;
  output[3] = 0;
  output[4] = input[u1dm] + input[r1m] * statein[v1];
  output[5] = input[v1dm] - input[r1m] * statein[u1];
  output[6] = input[u2dm] + input[r2m] * statein[v2];
  output[7] = input[v2dm] - input[r2m] * statein[u2];
  output[8] = input[r2m] - input[r1m];
}
 
/*
 * Measurement equation, measures range, height1, height2, u1, v1, u2, v2
 */
void discrete_ekf_no_north_hsym(float *statein, float *output)
{
  output[0] = powf(powf((statein[z1] - statein[z2]), 2.0) + powf(statein[x12], 2.0) + powf(statein[y12], 2.0), 0.5);
  output[1] = statein[z1];
  output[2] = statein[z2];
  output[3] = statein[u1];
  output[4] = statein[v1];
  output[5] = statein[u2];
  output[6] = statein[v2];
}
 
void discrete_ekf_no_north_Fx(float *statein, float *input, float **output)
{
  MAKE_MATRIX_PTR(_output, output, EKF_N);
  float_mat_zero(_output, EKF_N, EKF_N);
  output[0][1] = input[r1m];
  output[0][4] = -1;
  output[0][6] = cosf(statein[gam]);
  output[0][7] = -sinf(statein[gam]);
  output[0][8] = -statein[v2] * cosf(statein[gam]) - statein[u2] * sinf(statein[gam]);
  output[1][0] = -input[r1m];
  output[1][5] = -1;
  output[1][6] = sinf(statein[gam]);
  output[1][7] = cosf(statein[gam]);
  output[1][8] = statein[u2] * cosf(statein[gam]) - statein[v2] * sinf(statein[gam]);
  output[4][5] = input[r1m];
  output[5][4] = -input[r1m];
  output[6][7] = input[r2m];
  output[7][6] = -input[r2m];
}
 
void discrete_ekf_no_north_G(float *statein, float **output)
{
  MAKE_MATRIX_PTR(_output, output, EKF_N);
  float_mat_zero(_output, EKF_N, EKF_L);
  output[0][4] = statein[y12];
  output[1][4] = -statein[x12];
  output[4][0] = 1;
  output[4][4] = statein[v1];
  output[5][1] = 1;
  output[5][4] = -statein[u1];
  output[6][2] = 1;
  output[6][4] = statein[v2];
  output[7][3] = 1;
  output[7][4] = -statein[u2];
  output[8][4] = -1;
  output[8][5] = 1;
}
 
void discrete_ekf_no_north_Hx(float *statein, float **output)
{
  MAKE_MATRIX_PTR(_output, output, EKF_N);
  float_mat_zero(_output, EKF_M, EKF_N);
  output[0][0] = statein[x12] / (powf(powf(statein[z1] - statein[z2], 2.0) + powf(statein[x12], 2.0) + powf(statein[y12],
                                      2.0), 0.5));
  output[0][1] = statein[y12] / (powf(powf(statein[z1] - statein[z2], 2.0) + powf(statein[x12], 2.0) + powf(statein[y12],
                                      2.0), 0.5));
  output[0][2] = (2 * statein[z1] - 2 * statein[z2]) / (2 * powf(powf(statein[z1] - statein[z2], 2.0) + powf(statein[x12],
                 2.0) + powf(statein[y12], 2.0), 0.5));
  output[0][3] = -(2 * statein[z1] - 2 * statein[z2]) / (2 * powf(powf(statein[z1] - statein[z2],
                 2.0) + powf(statein[x12],
                             2.0) + powf(statein[y12], 2.0), 0.5));
  output[1][2] = 1;
  output[2][3] = 1;
  output[3][4] = 1;
  output[4][5] = 1;
  output[5][6] = 1;
  output[6][7] = 1;
}
 
/*
 * Initialize the filter
 */
void discrete_ekf_no_north_new(struct discrete_ekf_no_north *filter)
{
  MAKE_MATRIX_PTR(_P, filter->P, EKF_N);
  MAKE_MATRIX_PTR(_Q, filter->Q, EKF_N);
  MAKE_MATRIX_PTR(_R, filter->R, EKF_M);
 
  float_mat_diagonal_scal(_P, 16, EKF_N); // P Matrix
  float_mat_diagonal_scal(_Q, powf(2, 2), EKF_N); // Q Matrix [inputs: a1x, a1y, a2x, a2y, r1, r2]
  filter->Q[4][4] = powf(0.2, 2);
  filter->Q[5][5] = powf(0.2, 2);
 
  float_mat_diagonal_scal(_R, 0.7, EKF_M); // R Matrix [range, h1, h2, u1, v1, u2, v2]
  filter->R[0][0] = powf(0.5, 2);
  filter->R[1][1] = powf(0.2, 2);
  filter->R[2][2] = powf(0.2, 2);
 
  float_vect_zero(filter->X, EKF_N); // Initial state
  filter->X[0] =  1.0; // Initial X estimate
  filter->X[1] =  1.0; // Initial Y estimate
  filter->X[2] = -1.0; 
  filter->X[3] = -1.0;
  filter->dt = 0.1;  // Initial Est. time difference
}
 
/*
 * Perform the prediction step
 */
void discrete_ekf_no_north_predict(struct discrete_ekf_no_north *filter, float *U)
{
  float dX[EKF_N];
 
  MAKE_MATRIX_PTR(_tmp1, filter->tmp1, EKF_N);
  MAKE_MATRIX_PTR(_tmp2, filter->tmp2, EKF_N);
  MAKE_MATRIX_PTR(_tmp3, filter->tmp3, EKF_N);
  MAKE_MATRIX_PTR(_tmp4, filter->tmp4, EKF_N);
  MAKE_MATRIX_PTR(_P,    filter->P,    EKF_N);
  MAKE_MATRIX_PTR(_Q,    filter->Q,    EKF_N);
  MAKE_MATRIX_PTR(_H,    filter->H,    EKF_N);
  MAKE_MATRIX_PTR(_G,    filter->G,    EKF_N);
  MAKE_MATRIX_PTR(_Gamma, filter->Gamma, EKF_N);
  MAKE_MATRIX_PTR(_Phi,  filter->Phi,  EKF_N);
  MAKE_MATRIX_PTR(_Fx,   filter->Fx,   EKF_N);
 
  discrete_ekf_no_north_fsym(filter->X, U, dX);
  discrete_ekf_no_north_Fx(filter->X, U, _Fx);   // State transition matrix
  discrete_ekf_no_north_G(filter->X, _G);        // Input transition matrix
 
  float_vect_scale(dX, filter->dt, EKF_N);
  float_vect_sum(filter->Xp, filter->X, dX, EKF_N);
 
  c2d(EKF_N, EKF_N, EKF_L, _Fx, _G, filter->dt, _Phi, _Gamma);
 
  float_mat_mul(_tmp1, _Phi, _P, EKF_N, EKF_N, EKF_N);      // tmp1 <- Phi*P
  float_mat_transpose_square(_Phi, EKF_N);                  // tmp2 <- Phi'
  float_mat_mul(_tmp3, _tmp1, _Phi, EKF_N, EKF_N, EKF_N);   // tmp3 <- Phi*P*Phi'
 
  float_mat_mul(_tmp1, _Gamma, _Q, EKF_N, EKF_L, EKF_L);    // tmp1 <- Gamma*Q
  float_mat_transpose(_tmp2, _Gamma, EKF_N, EKF_L);         // tmp2 <- Gamma'
  float_mat_mul(_tmp4, _tmp1, _tmp2, EKF_N, EKF_L, EKF_N);  // tmp4 <- Gamma*Q*Gamma
 
  float_mat_sum(_P, _tmp3, _tmp4, EKF_N, EKF_N);            // P <- Phi*P*Phi' + Gamma*Q*Gamma'
 
  discrete_ekf_no_north_hsym(filter->Xp, filter->Zp);
  discrete_ekf_no_north_Hx(filter->Xp, _H);
}
 
/* Perform the update step
 
    Get Kalman Gain
      P12 = P * H';
      K = P12/(H * P12 + R);
 
    Update x
      x = x_p + K * (z - z_p);
 
    Update P
      P = (eye(numel(x)) - K * H) * P;
*/
void discrete_ekf_no_north_update(struct discrete_ekf_no_north *filter, float *Z)
{
  MAKE_MATRIX_PTR(_tmp1, filter->tmp1, EKF_N);
  MAKE_MATRIX_PTR(_tmp2, filter->tmp2, EKF_N);
  MAKE_MATRIX_PTR(_tmp3, filter->tmp3, EKF_N);
  MAKE_MATRIX_PTR(_P,    filter->P,    EKF_N);
  MAKE_MATRIX_PTR(_H,    filter->H,    EKF_M);
  MAKE_MATRIX_PTR(_Ht,   filter->Ht,   EKF_N);
  MAKE_MATRIX_PTR(_R,    filter->R,    EKF_M);
 
  //  E = H * P * H' + R
  float_mat_transpose(_Ht, _H, EKF_M, EKF_N); // Ht = H'
  float_mat_mul(_tmp2, _P, _Ht, EKF_N, EKF_N, EKF_M); // tmp2 = P*Ht = P*H'
  float_mat_mul(_tmp1, _H, _tmp2, EKF_M, EKF_N, EKF_M); // tmp1 = H*P*H'
  float_mat_sum(_tmp3, _tmp1, _R, EKF_M, EKF_M); // E = tmp1(=H*P*H') + R
 
  // K = P * H' * inv(E)
  float_mat_invert(_tmp1, _tmp3, EKF_M); // tmp1 = inv(E)
  float_mat_mul(_tmp3, _tmp2, _tmp1, EKF_N, EKF_M, EKF_M); // K(tmp3) = tmp2*tmp1
 
  // P = P - K * H * P
  float_mat_mul(_tmp1, _tmp3, _H, EKF_N, EKF_M, EKF_N); // tmp1 = K*H
  float_mat_mul(_tmp2, _tmp1, _P, EKF_N, EKF_N, EKF_N); // tmp3 = K*H*P
  float_mat_diff(_P, _P, _tmp2, EKF_N, EKF_N); // P - K*H*P
 
  //  X = X + K * err
  float err[EKF_M];
  float dx_err[EKF_N];
 
  float_vect_diff(err, Z, filter->Zp, EKF_M); // err = Z - Zp
  float_mat_vect_mul(dx_err, _tmp3, err, EKF_N, EKF_M); // dx_err = K*err
  float_vect_sum(filter->X, filter->Xp, dx_err, EKF_N); // X = Xp + dx_err
}