vio/svo/src/matcher.cpp

// This file is part of SVO - Semi-direct Visual Odometry.
//
// Copyright (C) 2014 Christian Forster <forster at ifi dot uzh dot ch>
// (Robotics and Perception Group, University of Zurich, Switzerland).
//
// SVO 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 3 of the License, or any later version.
//
// SVO 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 this program.  If not, see <http://www.gnu.org/licenses/>.

#include <cstdlib>
#include <vikit/abstract_camera.h>
#include <vikit/vision.h>
#include <vikit/math_utils.h>
#include <vikit/aligned_mem.h>
#include <vikit/patch_score.h>
#include <svo/matcher.h>
#include <svo/frame.h>
#include <svo/feature.h>
#include <svo/point.h>
#include <svo/config.h>
#include <svo/feature_alignment.h>

namespace svo {

namespace warp {

void getWarpMatrixAffine(
    const vk::AbstractCamera& cam_ref,
    const vk::AbstractCamera& cam_cur,
    const Vector2d& px_ref,
    const Vector3d& f_ref,
    const double depth_ref,
    const SE3& T_cur_ref,
    const int level_ref,
    Matrix2d& A_cur_ref)
{
  // Compute affine warp matrix A_ref_cur
  const int halfpatch_size = 5;
  const Vector3d xyz_ref(f_ref*depth_ref);
  Vector3d xyz_du_ref(cam_ref.cam2world(px_ref + Vector2d(halfpatch_size,0)*(1<<level_ref)));
  Vector3d xyz_dv_ref(cam_ref.cam2world(px_ref + Vector2d(0,halfpatch_size)*(1<<level_ref)));
  xyz_du_ref *= xyz_ref[2]/xyz_du_ref[2];
  xyz_dv_ref *= xyz_ref[2]/xyz_dv_ref[2];
  const Vector2d px_cur(cam_cur.world2cam(T_cur_ref*(xyz_ref)));
  const Vector2d px_du(cam_cur.world2cam(T_cur_ref*(xyz_du_ref)));
  const Vector2d px_dv(cam_cur.world2cam(T_cur_ref*(xyz_dv_ref)));
  A_cur_ref.col(0) = (px_du - px_cur)/halfpatch_size;
  A_cur_ref.col(1) = (px_dv - px_cur)/halfpatch_size;
}

int getBestSearchLevel(
    const Matrix2d& A_cur_ref,
    const int max_level)
{
  // Compute patch level in other image
  int search_level = 0;
  double D = A_cur_ref.determinant();
  while(D > 3.0 && search_level < max_level)
  {
    search_level += 1;
    D *= 0.25;
  }
  return search_level;
}

void warpAffine(
    const Matrix2d& A_cur_ref,
    const cv::Mat& img_ref,
    const Vector2d& px_ref,
    const int level_ref,
    const int search_level,
    const int halfpatch_size,
    uint8_t* patch)
{
  const int patch_size = halfpatch_size*2 ;
  const Matrix2f A_ref_cur = A_cur_ref.inverse().cast<float>();
  if(isnan(A_ref_cur(0,0)))
  {
    printf("Affine warp is NaN, probably camera has no translation\n"); // TODO
    return;
  }

  // Perform the warp on a larger patch.
  uint8_t* patch_ptr = patch;
  const Vector2f px_ref_pyr = px_ref.cast<float>() / (1<<level_ref);
  for (int y=0; y<patch_size; ++y)
  {
    for (int x=0; x<patch_size; ++x, ++patch_ptr)
    {
      Vector2f px_patch(x-halfpatch_size, y-halfpatch_size);
      px_patch *= (1<<search_level);
      const Vector2f px(A_ref_cur*px_patch + px_ref_pyr);
      if (px[0]<0 || px[1]<0 || px[0]>=img_ref.cols-1 || px[1]>=img_ref.rows-1)
        *patch_ptr = 0;
      else
        *patch_ptr = (uint8_t) vk::interpolateMat_8u(img_ref, px[0], px[1]);
    }
  }
}

} // namespace warp


Matcher::Matcher()
{
  patch_ = vk::aligned_mem::aligned_alloc<uint8_t>(patch_size_*patch_size_, 16);
  patch_with_border_ = vk::aligned_mem::aligned_alloc<uint8_t>((patch_size_+2)*(patch_size_+2), 16);
}

Matcher::~Matcher()
{
  free(patch_);
  free(patch_with_border_);
}

bool depthFromTriangulation(
    const SE3& T_search_ref,
    const Vector3d& f_ref,
    const Vector3d& f_cur,
    double& depth)
{
  Matrix<double,3,2> A; A << T_search_ref.rotation_matrix() * f_ref, f_cur;
  const Matrix2d AtA = A.transpose()*A;
  if(AtA.determinant() < 0.000001)
    return false;
  const Vector2d depth2 = - AtA.inverse()*A.transpose()*T_search_ref.translation();
  depth = fabs(depth2[0]);
  return true;
}

void Matcher::createPatchFromPatchWithBorder()
{
  uint8_t* ref_patch_ptr = patch_;
  for(int y=1; y<patch_size_+1; ++y, ref_patch_ptr += patch_size_)
  {
    uint8_t* ref_patch_border_ptr = patch_with_border_ + y*(patch_size_+2) + 1;
    for(int x=0; x<patch_size_; ++x)
      ref_patch_ptr[x] = ref_patch_border_ptr[x];
  }
}

bool Matcher::findMatchDirect(
    const Point& pt,
    const Frame& cur_frame,
    Vector2d& px_cur)
{
  if(!pt.getCloseViewObs(cur_frame.pos(), ref_ftr_))
    return false;

  if(!ref_ftr_->frame->cam_->isInFrame(
      ref_ftr_->px.cast<int>()/(1<<ref_ftr_->level), halfpatch_size_+2, ref_ftr_->level))
    return false;

  // warp affine
  warp::getWarpMatrixAffine(
      *ref_ftr_->frame->cam_, *cur_frame.cam_, ref_ftr_->px, ref_ftr_->f,
      (ref_ftr_->frame->pos() - pt.pos_).norm(),
      cur_frame.T_f_w_ * ref_ftr_->frame->T_f_w_.inverse(), ref_ftr_->level, A_cur_ref_);
  search_level_ = warp::getBestSearchLevel(A_cur_ref_, Config::nPyrLevels()-1);
  warp::warpAffine(A_cur_ref_, ref_ftr_->frame->img_pyr_[ref_ftr_->level], ref_ftr_->px,
                   ref_ftr_->level, search_level_, halfpatch_size_+1, patch_with_border_);
  createPatchFromPatchWithBorder();

  // px_cur should be set
  Vector2d px_scaled(px_cur/(1<<search_level_));
  bool success = feature_alignment::align2D(
      cur_frame.img_pyr_[search_level_], patch_with_border_, patch_,
      options_.align_max_iter, px_scaled);
  px_cur = px_scaled * (1<<search_level_);
  return success;
}

bool Matcher::findEpipolarMatchDirect(
    const Frame& ref_frame,
    const Frame& cur_frame,
    const Feature& ref_ftr,
    const double d_estimate,
    const double d_min,
    const double d_max,
    double& depth)
{
  SE3 T_cur_ref = cur_frame.T_f_w_ * ref_frame.T_f_w_.inverse();
  int zmssd_best = PatchScore::threshold();
  Vector2d uv_best;

  // Compute start and end of epipolar line in old_kf for match search, on unit plane!
  Vector2d A = vk::project2d(T_cur_ref * (ref_ftr.f*d_min));
  Vector2d B = vk::project2d(T_cur_ref * (ref_ftr.f*d_max));
  Vector2d epi_dir = A - B;

  // Compute affine warp matrix
  warp::getWarpMatrixAffine(
      *ref_frame.cam_, *cur_frame.cam_, ref_ftr.px, ref_ftr.f,
      d_estimate, T_cur_ref, ref_ftr.level, A_cur_ref_);
  search_level_ = warp::getBestSearchLevel(A_cur_ref_, Config::nPyrLevels()-1);

  // Find length of search range on epipolar line
  Vector2d px_A(cur_frame.cam_->world2cam(A));
  Vector2d px_B(cur_frame.cam_->world2cam(B));
  epi_length_ = (px_A-px_B).norm() / (1<<search_level_);

  // Warp reference patch at ref_level
  warp::warpAffine(A_cur_ref_, ref_frame.img_pyr_[ref_ftr.level], ref_ftr.px,
                   ref_ftr.level, search_level_, halfpatch_size_+1, patch_with_border_);
  createPatchFromPatchWithBorder();

  if(epi_length_ < 2.0)
  {
    px_cur_ = (px_A+px_B)/2.0;
    Vector2d px_scaled(px_cur_/(1<<search_level_));
    bool res;
    if(options_.align_1d)
      res = feature_alignment::align1D(
          cur_frame.img_pyr_[search_level_], (px_A-px_B).cast<float>().normalized(),
          patch_with_border_, patch_, options_.align_max_iter, px_scaled, h_inv_);
    else
      res = feature_alignment::align2D(
          cur_frame.img_pyr_[search_level_], patch_with_border_, patch_,
          options_.align_max_iter, px_scaled);
    if(res)
    {
      px_cur_ = px_scaled*(1<<search_level_);
      if(depthFromTriangulation(T_cur_ref, ref_ftr.f, cur_frame.cam_->cam2world(px_cur_), depth))
        return true;
    }
    return false;
  }

  size_t n_steps = epi_length_/0.7; // one step per pixel
  Vector2d step = epi_dir/n_steps;

  if(n_steps > options_.max_epi_search_steps)
  {
    printf("WARNING: skip epipolar search: %zu evaluations, px_lenght=%f, d_min=%f, d_max=%f.\n",
           n_steps, epi_length_, d_min, d_max);
    return false;
  }

  // for matching, precompute sum and sum2 of warped reference patch
  int pixel_sum = 0;
  int pixel_sum_square = 0;
  PatchScore patch_score(patch_);

  // now we sample along the epipolar line
  Vector2d uv = B-step;
  Vector2i last_checked_pxi(0,0);
  ++n_steps;
  for(size_t i=0; i<n_steps; ++i, uv+=step)
  {
    Vector2d px(cur_frame.cam_->world2cam(uv));
    Vector2i pxi(px[0]/(1<<search_level_)+0.5,
                 px[1]/(1<<search_level_)+0.5); // +0.5 to round to closest int

    if(pxi == last_checked_pxi)
      continue;
    last_checked_pxi = pxi;

    // check if the patch is full within the new frame
    if(!cur_frame.cam_->isInFrame(pxi, patch_size_, search_level_))
      continue;

    // TODO interpolation would probably be a good idea
    uint8_t* cur_patch_ptr = cur_frame.img_pyr_[search_level_].data
                             + (pxi[1]-halfpatch_size_)*cur_frame.img_pyr_[search_level_].cols
                             + (pxi[0]-halfpatch_size_);
    int zmssd = patch_score.computeScore(cur_patch_ptr, cur_frame.img_pyr_[search_level_].cols);

    if(zmssd < zmssd_best) {
      zmssd_best = zmssd;
      uv_best = uv;
    }
  }

  if(zmssd_best < PatchScore::threshold())
  {
    if(options_.subpix_refinement)
    {
      px_cur_ = cur_frame.cam_->world2cam(uv_best);
      Vector2d px_scaled(px_cur_/(1<<search_level_));
      bool res;
      if(options_.align_1d)
        res = feature_alignment::align1D(
            cur_frame.img_pyr_[search_level_], (px_A-px_B).cast<float>().normalized(),
            patch_with_border_, patch_, options_.align_max_iter, px_scaled, h_inv_);
      else
        res = feature_alignment::align2D(
            cur_frame.img_pyr_[search_level_], patch_with_border_, patch_,
            options_.align_max_iter, px_scaled);
      if(res)
      {
        px_cur_ = px_scaled*(1<<search_level_);
        if(depthFromTriangulation(T_cur_ref, ref_ftr.f, cur_frame.cam_->cam2world(px_cur_), depth))
          return true;
      }
      return false;
    }
    px_cur_ = cur_frame.cam_->world2cam(uv_best);
    if(depthFromTriangulation(T_cur_ref, ref_ftr.f, vk::unproject2d(uv_best).normalized(), depth))
      return true;
  }
  return false;
}

} // namespace svo