footprint_helper.cpp

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#include "mbf_costmap_nav/footprint_helper.h"
 
namespace mbf_costmap_nav
{
 
void FootprintHelper::getLineCells(int x0, int x1, int y0, int y1, std::vector<Cell>& pts) {
  //Bresenham Ray-Tracing
  int deltax = abs(x1 - x0);        // The difference between the x's
  int deltay = abs(y1 - y0);        // The difference between the y's
  int x = x0;                       // Start x off at the first pixel
  int y = y0;                       // Start y off at the first pixel
 
  int xinc1, xinc2, yinc1, yinc2;
  int den, num, numadd, numpixels;
 
  Cell pt;
 
  if (x1 >= x0)                 // The x-values are increasing
  {
    xinc1 = 1;
    xinc2 = 1;
  }
  else                          // The x-values are decreasing
  {
    xinc1 = -1;
    xinc2 = -1;
  }
 
  if (y1 >= y0)                 // The y-values are increasing
  {
    yinc1 = 1;
    yinc2 = 1;
  }
  else                          // The y-values are decreasing
  {
    yinc1 = -1;
    yinc2 = -1;
  }
 
  if (deltax >= deltay)         // There is at least one x-value for every y-value
  {
    xinc1 = 0;                  // Don't change the x when numerator >= denominator
    yinc2 = 0;                  // Don't change the y for every iteration
    den = deltax;
    num = deltax / 2;
    numadd = deltay;
    numpixels = deltax;         // There are more x-values than y-values
  }
  else                          // There is at least one y-value for every x-value
  {
    xinc2 = 0;                  // Don't change the x for every iteration
    yinc1 = 0;                  // Don't change the y when numerator >= denominator
    den = deltay;
    num = deltay / 2;
    numadd = deltax;
    numpixels = deltay;         // There are more y-values than x-values
  }
 
  for (int curpixel = 0; curpixel <= numpixels; curpixel++)
  {
    pt.x = x;      //Draw the current pixel
    pt.y = y;
    pts.push_back(pt);
 
    num += numadd;              // Increase the numerator by the top of the fraction
    if (num >= den)             // Check if numerator >= denominator
    {
      num -= den;               // Calculate the new numerator value
      x += xinc1;               // Change the x as appropriate
      y += yinc1;               // Change the y as appropriate
    }
    x += xinc2;                 // Change the x as appropriate
    y += yinc2;                 // Change the y as appropriate
  }
}
 
 
void FootprintHelper::getFillCells(std::vector<Cell>& footprint){
  //quick bubble sort to sort pts by x
  Cell swap, pt;
  unsigned int i = 0;
  while (i < footprint.size() - 1) {
    if (footprint[i].x > footprint[i + 1].x) {
      swap = footprint[i];
      footprint[i] = footprint[i + 1];
      footprint[i + 1] = swap;
      if(i > 0) {
        --i;
      }
    } else {
      ++i;
    }
  }
 
  i = 0;
  Cell min_pt;
  Cell max_pt;
  unsigned int min_x = footprint[0].x;
  unsigned int max_x = footprint[footprint.size() -1].x;
  //walk through each column and mark cells inside the footprint
  for (unsigned int x = min_x; x <= max_x; ++x) {
    if (i >= footprint.size() - 1) {
      break;
    }
    if (footprint[i].y < footprint[i + 1].y) {
      min_pt = footprint[i];
      max_pt = footprint[i + 1];
    } else {
      min_pt = footprint[i + 1];
      max_pt = footprint[i];
    }
 
    i += 2;
    while (i < footprint.size() && footprint[i].x == x) {
      if(footprint[i].y < min_pt.y) {
        min_pt = footprint[i];
      } else if(footprint[i].y > max_pt.y) {
        max_pt = footprint[i];
      }
      ++i;
    }
 
    //loop though cells in the column
    for (unsigned int y = min_pt.y; y < max_pt.y; ++y) {
      pt.x = x;
      pt.y = y;
      footprint.push_back(pt);
    }
  }
}
 
static const std::vector<Cell>& clearAndReturn(std::vector<Cell>& _cells)
{
  _cells.clear();
  return _cells;
}
 
std::vector<Cell> FootprintHelper::getFootprintCells(double x, double y, double theta,
                                                     const std::vector<geometry_msgs::Point>& footprint_spec,
                                                     const costmap_2d::Costmap2D& costmap, bool fill)
{
  std::vector<Cell> footprint_cells;
 
  //if we have no footprint... do nothing
  if (footprint_spec.size() <= 1) {
    unsigned int mx, my;
    if (costmap.worldToMap(x, y, mx, my)) {
      Cell center;
      center.x = mx;
      center.y = my;
      footprint_cells.push_back(center);
    }
    return footprint_cells;
  }
 
  //pre-compute cos and sin values
  double cos_th = cos(theta);
  double sin_th = sin(theta);
  double new_x, new_y;
  unsigned int x0, y0, x1, y1;
  unsigned int last_index = footprint_spec.size() - 1;
 
  for (unsigned int i = 0; i < last_index; ++i) {
    //find the cell coordinates of the first segment point
    new_x = x + (footprint_spec[i].x * cos_th - footprint_spec[i].y * sin_th);
    new_y = y + (footprint_spec[i].x * sin_th + footprint_spec[i].y * cos_th);
    if(!costmap.worldToMap(new_x, new_y, x0, y0)) {
      return clearAndReturn(footprint_cells);
    }
 
    //find the cell coordinates of the second segment point
    new_x = x + (footprint_spec[i + 1].x * cos_th - footprint_spec[i + 1].y * sin_th);
    new_y = y + (footprint_spec[i + 1].x * sin_th + footprint_spec[i + 1].y * cos_th);
    if (!costmap.worldToMap(new_x, new_y, x1, y1)) {
      return clearAndReturn(footprint_cells);
    }
 
    getLineCells(x0, x1, y0, y1, footprint_cells);
  }
 
  //we need to close the loop, so we also have to raytrace from the last pt to first pt
  new_x = x + (footprint_spec[last_index].x * cos_th - footprint_spec[last_index].y * sin_th);
  new_y = y + (footprint_spec[last_index].x * sin_th + footprint_spec[last_index].y * cos_th);
  if (!costmap.worldToMap(new_x, new_y, x0, y0)) {
    return clearAndReturn(footprint_cells);
  }
  new_x = x + (footprint_spec[0].x * cos_th - footprint_spec[0].y * sin_th);
  new_y = y + (footprint_spec[0].x * sin_th + footprint_spec[0].y * cos_th);
  if(!costmap.worldToMap(new_x, new_y, x1, y1)) {
    return clearAndReturn(footprint_cells);
  }
 
  getLineCells(x0, x1, y0, y1, footprint_cells);
 
  if(fill) {
    getFillCells(footprint_cells);
  }
 
  return footprint_cells;
}
 
} /* namespace mbf_costmap_nav */