ExpToLevelSetxt.cpp

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#ifdef HAVE_CONFIG_H
   #include <config.h>
#else
#error "Cannot compile with HAVE_CONFIG_H symbol! run configure first!"
#endif
 
/*Include files*/
#include "./ExpToLevelSetx.h"
double minimum_distance(double x1, double y1, double x2, double y2, double x0, double y0);
void   ContourToLevelSet(double* distance,double* contourx, double* contoury, int contournods, double* x, double* y, int i0, int i10);
 
void* ExpToLevelSetxt(void* vpthread_handle){
 
   /*gate variables :*/
   ExpToLevelSetxThreadStruct *gate        = NULL;
   pthread_handle             *handle      = NULL;
   int  i,i1,i0;
 
   /*recover handle and gate: */
   handle          = (pthread_handle*)vpthread_handle;
   gate            = (ExpToLevelSetxThreadStruct*)handle->gate;
   int my_thread   = handle->id;
   int num_threads = handle->num;
 
   /*recover parameters :*/
   Contours* contours = gate->contours;
   int       nods     = gate->nods;
   double   *distance = gate->distance;
   double   *x        = gate->x;
   double   *y        = gate->y;
 
   /*distribute indices across threads :*/
   PartitionRange(&i0,&i1,nods,num_threads,my_thread);
 
   /*Loop through all contours: */
   for(i=0;i<contours->Size();i++){
      Contour<double>* contour=(Contour<double>*)contours->GetObjectByOffset(i);
      ContourToLevelSet(distance,contour->x,contour->y,contour->nods,x,y,i0,i1);
   }
 
   return NULL;
}
 
void ContourToLevelSet(double* dist,double* contourx, double* contoury, int contournods, double* x, double* y, int i0, int i1){/*{{{*/
 
   double x0,y0;
   double x1,y1;
   double x2,y2;
   double mind;
 
   for(int i=i0;i<i1;i++){
 
      /*Get current point*/
      x0=x[i]; y0=y[i];
 
      /*Figure out distance from (x0,y0) to contour: */
      mind=1e+50;
      for(int j=0;j<contournods-1;j++){
         /*Get distance from current segment*/
         x1=contourx[j];   y1=contoury[j];
         x2=contourx[j+1]; y2=contoury[j+1];
         mind=min(mind,minimum_distance(x1,y1,x2,y2,x0,y0));
      }
      dist[i]=min(dist[i],mind);
   }
}
double minimum_distance(double x1, double y1, double x2, double y2, double x0, double y0){
   /* Return minimum distance between line segment [(x1,y1) (x2,y2)] and point (x0,y0)
    * We use the following notations:
    * segment: v=(x1,y1), w=(x2,y2)
    * point:   p=(x0,y0) 
    */
 
   /*Get segment length square (avoid sqrt) |w-v|^2*/
   double l2 = pow(x2-x1,2)+pow(y2-y1,2); 
 
   /*segment is single point: v == w*/
   if(l2 == 0.) return sqrt(pow(x1-x0,2)+pow(y1-y0,2));
 
   /*Consider the line extending the segment, parameterized as v + t (w - v).
   We find projection of point p onto the line.  It falls where t = [(p-v) . (w-v)] / |w-v|^2*/
   double t = ((x0-x1)*(x2-x1) + (y0-y1)*(y2-y1)) / l2;
   if(t < 0.){
      /*Beyond the 'v' end of the segment*/
      return sqrt(pow(x1-x0,2)+pow(y1-y0,2));
   }
   else if(t > 1.){
      /*Beyond the 'w' end of the segment*/
      return sqrt(pow(x2-x0,2)+pow(y2-y0,2));
   }
 
   /*Projection falls on segment*/
   double projx= x1 + t* (x2-x1);
   double projy= y1 + t* (y2-y1);
   return sqrt(pow(projx-x0,2)+pow(projy-y0,2));
}
/*}}}*/