PnP_AHRS.c

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/*
 * Copyright (C) Guido de Croon, 2018
 *
 * 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/>.
 */
 
// Own Header
#include "PnP_AHRS.h"
#include "state.h"
#include <stdio.h>
 
// #define DEBUG_PNP
 
struct FloatVect3 get_world_position_from_image_points(int *x_corners, int *y_corners, struct FloatVect3 *world_corners,
    int n_corners, struct camera_intrinsics_t cam_intrinsics, struct FloatEulers cam_body)
{
 
  // legend:
  // E = Earth
  // B = body
  // C = camera
 
  struct FloatVect3 pos_drone_E_vec;
  FLOAT_VECT3_ZERO(pos_drone_E_vec);
 
  // Make an identity matrix:
  static struct FloatRMat I_mat;
  FLOAT_MAT33_DIAG(I_mat, 1., 1., 1.);
 
  static struct FloatRMat Q_mat;
  FLOAT_MAT33_ZERO(Q_mat);
 
  //camera to body rotation
  struct FloatRMat R_E_B, R_B_E, R_C_B;
  float_rmat_of_eulers_321(&R_C_B, &cam_body);
 
  // Use the AHRS roll and pitch from the filter to get the attitude in a rotation matrix R_E_B:
  struct FloatEulers attitude;
  attitude.phi =    stateGetNedToBodyEulers_f()->phi;//positive ccw
  attitude.theta = stateGetNedToBodyEulers_f()->theta;//negative downward
  // local_psi typically assumed 0.0f (meaning you are straight in front of the object):
  // If you want to use the estimate of psi, stateGetNedToBodyEulers_f()->psi, then you still need to take the psi of the gate into account.
  float local_psi = 0.0f; // stateGetNedToBodyEulers_f()->psi; // 0.0f;
  attitude.psi = local_psi;
  float_rmat_of_eulers_321(&R_E_B, &attitude);
  MAT33_TRANS(R_B_E, R_E_B);
 
  // Camera calibration matrix:
  float K[9] = {cam_intrinsics.focal_x, 0.0f, cam_intrinsics.center_x,
                0.0f, cam_intrinsics.focal_y, cam_intrinsics.center_y,
                0.0f, 0.0f, 1.0f
               };
 
  // vectors in world coordinates, that will be "attached" to the world coordinates for the PnP:
  struct FloatVect3 gate_vectors[4], vec_B, vec_E, p_vec, temp_vec;
  FLOAT_VECT3_ZERO(p_vec);
 
  // Solution from: http://cal.cs.illinois.edu/~johannes/research/LS_line_intersect.pdf
  // Equivalent MATLAB code:
  //
  // for i = 1:4
  //    Q = Q + (eye(3,3)-n(:,i)*n(:,i)');
  //    p = p + (eye(3,3)-n(:,i)*n(:,i)')*a(:,i);
  //
  // where n is the normalized vector, and a is the world coordinate
 
  struct FloatRMat temp_mat, temp_mat_2;
  FLOAT_MAT33_ZERO(temp_mat);
 
  // Construct the matrix for linear least squares:
  for (int i = 0; i < n_corners; i++) {
 
    // undistort the image coordinate and put it in a world vector:
    float x_n, y_n;
    bool success = distorted_pixels_to_normalized_coords((float) x_corners[i], (float) y_corners[i], &x_n, &y_n, cam_intrinsics.Dhane_k, K);
    if(!success) {
      printf("Undistortion not possible in PnPAHRS.c... why?\n");
      return pos_drone_E_vec;
    }
 
    gate_vectors[i].x = 1.0; // positive to the front
    gate_vectors[i].y = y_n; // positive to the right
    gate_vectors[i].z = -x_n; // positive down
 
    // transform the vector to the gate corner to earth coordinates:
    MAT33_VECT3_MUL(vec_B, R_C_B, gate_vectors[i]);
    double vec_norm = sqrt(VECT3_NORM2(vec_B));
    VECT3_SDIV(vec_B, vec_B, vec_norm);
    MAT33_VECT3_MUL(vec_E, R_B_E, vec_B);
 
#ifdef DEBUG_PNP
    printf("Determine world vector for corner %d\n", i);
    printf("Distorted coordinates: (x,y) = (%d, %d)\n", x_corners[i], y_corners[i]);
    printf("Normalized coordinates: (x_n, y_n) = (%f, %f)\n", x_n, y_n);
    printf("Gate vector: (%f,%f,%f)\n", gate_vectors[i].x, gate_vectors[i].y, gate_vectors[i].z);
    printf("Gate vector to Body: (%f,%f,%f)\n", vec_B.x, vec_B.y, vec_B.z);
    printf("Gate vector to World: (%f,%f,%f)\n", vec_E.x, vec_E.y, vec_E.z);
    printf("Euler angles body: (pitch, roll, yaw) = (%f, %f, %f)\n", attitude.theta, attitude.phi, attitude.psi);
    printf("World corner %d: (%f, %f, %f)\n", i, world_corners[i].x, world_corners[i].y, world_corners[i].z);
#endif
 
    VECT3_VECT3_TRANS_MUL(temp_mat, vec_E, vec_E); // n(:,i)*n(:,i)'
    MAT33_MAT33_DIFF(temp_mat, I_mat, temp_mat); // (eye(3,3)-n(:,i)*n(:,i)')
    MAT33_COPY(temp_mat_2, Q_mat);
    MAT33_MAT33_SUM(Q_mat, temp_mat_2, temp_mat); // Q + (eye(3,3)-n(:,i)*n(:,i)')
    MAT33_VECT3_MUL(temp_vec, temp_mat, world_corners[i]); // (eye(3,3)-n(:,i)*n(:,i)')*a(:,i)
    VECT3_SUM(p_vec, p_vec, temp_vec); // p + (eye(3,3)-n(:,i)*n(:,i)')*a(:,i);
  }
 
  // Solve the linear system:
  MAT33_INV(temp_mat, Q_mat);
  MAT33_VECT3_MUL(pos_drone_E_vec, temp_mat, p_vec); // position = inv(Q) * p
 
#if CAMERA_ROTATED_90DEG_RIGHT
  // transformation of coordinates
  float temp = pos_drone_E_vec.y;
  pos_drone_E_vec.y = -pos_drone_E_vec.z;
  pos_drone_E_vec.z = -temp;
#endif
 
  //bound y to remove outliers
  float y_threshold = 4;
  if (pos_drone_E_vec.y > y_threshold) { pos_drone_E_vec.y = y_threshold; }
  else if (pos_drone_E_vec.y < -y_threshold) { pos_drone_E_vec.y = -y_threshold; }
 
  return pos_drone_E_vec;
}