ear_clipping.cpp

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 * $Id: ear_clipping.cpp 5027 2012-03-12 03:10:45Z rusu $
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#include <pcl/surface/ear_clipping.h>
#include <pcl/ros/conversions.h>
#include <pcl/pcl_config.h>

bool
pcl::EarClipping::initCompute ()
{
  points_.reset (new pcl::PointCloud<pcl::PointXYZ>);

  if (!MeshProcessing::initCompute ())
    return (false);
  fromROSMsg (input_mesh_->cloud, *points_);

  return (true);
}

void
pcl::EarClipping::performProcessing (PolygonMesh& output)
{
  output.polygons.clear ();
  output.cloud = input_mesh_->cloud;
  for (int i = 0; i < static_cast<int> (input_mesh_->polygons.size ()); ++i)
    triangulate (input_mesh_->polygons[i], output);
}

void
pcl::EarClipping::triangulate (const Vertices& vertices, PolygonMesh& output)
{
  const int n_vertices = static_cast<const int> (vertices.vertices.size ());

  if (n_vertices <= 3)
    return;

  std::vector<uint32_t> remaining_vertices (n_vertices);
  if (area (vertices.vertices) > 0) // clockwise?
    remaining_vertices = vertices.vertices;
  else
    for (int v = 0; v < n_vertices; v++)
      remaining_vertices[v] = vertices.vertices[n_vertices - 1 - v];

  // Avoid closed loops.
  if (remaining_vertices.front () == remaining_vertices.back ())
    remaining_vertices.erase (remaining_vertices.end () - 1);

  // null_iterations avoids infinite loops if the polygon is not simple.
  for (int u = static_cast<int> (remaining_vertices.size ()) - 1, null_iterations = 0;
      remaining_vertices.size () > 2 && null_iterations < static_cast<int >(remaining_vertices.size () * 2);
      ++null_iterations, u = (u+1) % static_cast<int> (remaining_vertices.size ()))
  {
    int v = (u + 1) % static_cast<int> (remaining_vertices.size ());
    int w = (u + 2) % static_cast<int> (remaining_vertices.size ());

    if (isEar (u, v, w, remaining_vertices))
    {
      Vertices triangle;
      triangle.vertices.resize (3);
      triangle.vertices[0] = remaining_vertices[u];
      triangle.vertices[1] = remaining_vertices[v];
      triangle.vertices[2] = remaining_vertices[w];
      output.polygons.push_back (triangle);
      remaining_vertices.erase (remaining_vertices.begin () + v);
      null_iterations = 0;
    }
  }
}


float
pcl::EarClipping::area (const std::vector<uint32_t>& vertices)
{
  int n = static_cast<int> (vertices.size ());
  float area = 0.0f;
  Eigen::Vector2f prev_p, cur_p;
  for (int prev = n - 1, cur = 0; cur < n; prev = cur++)
  {
    prev_p[0] = points_->points[vertices[prev]].x;
    prev_p[1] = points_->points[vertices[prev]].y;
    cur_p[0] = points_->points[vertices[cur]].x;
    cur_p[1] = points_->points[vertices[cur]].y;

    area += crossProduct (prev_p, cur_p);
  }
  return (area * 0.5f);
}


bool
pcl::EarClipping::isEar (int u, int v, int w, const std::vector<uint32_t>& vertices)
{
  Eigen::Vector2f p_u, p_v, p_w;
  p_u[0] = points_->points[vertices[u]].x;
  p_u[1] = points_->points[vertices[u]].y;
  p_v[0] = points_->points[vertices[v]].x;
  p_v[1] = points_->points[vertices[v]].y;
  p_w[0] = points_->points[vertices[w]].x;
  p_w[1] = points_->points[vertices[w]].y;

  // Avoid flat triangles.
  // FIXME: triangulation would fail if all the triangles are flat in the X-Y axis
  const float eps = 1e-15f;
  Eigen::Vector2f p_uv, p_uw;
  p_uv = p_v - p_u;
  p_uw = p_w - p_u;
  if (crossProduct (p_uv, p_uw) < eps)
    return (false);

  Eigen::Vector2f p;
  // Check if any other vertex is inside the triangle.
  for (int k = 0; k < static_cast<int> (vertices.size ()); k++)
  {
    if ((k == u) || (k == v) || (k == w))
      continue;
    p[0] = points_->points[vertices[k]].x;
    p[1] = points_->points[vertices[k]].y;

    if (isInsideTriangle (p_u, p_v, p_w, p))
      return (false);
  }
  return (true);
}

bool
pcl::EarClipping::isInsideTriangle (const Eigen::Vector2f& u,
                                    const Eigen::Vector2f& v,
                                    const Eigen::Vector2f& w,
                                    const Eigen::Vector2f& p)
{
  // Check first side.
  if (crossProduct (w - v, p - v) < 0)
    return (false);

  // Check second side.
  if (crossProduct (v - u, p - u) < 0)
    return (false);

  // Check third side.
  if (crossProduct (u - w, p - w) < 0)
    return (false);

  return (true);
}