pointInsideContour.c File Reference

Provides functions for determining the relative position of points with respect to a polygonal contour, including whether a point lies inside it. More...

#include "mdb.h"

Go to the source code of this file.

Functions
double	pointIsLeftOfLine (int64_t i1, int64_t i2, double *x, double *y, double x0, double y0)
int	pointIsInsideContour (double x0, double y0, double *x, double *y, int64_t n, double *center, double theta)
	Determine if a given point (x0, y0) is inside a specified polygonal contour.

Detailed Description

Provides functions for determining the relative position of points with respect to a polygonal contour, including whether a point lies inside it.

Copyright

• (c) 2002 The University of Chicago, as Operator of Argonne National Laboratory.
• (c) 2002 The Regents of the University of California, as Operator of Los Alamos National Laboratory.

License

This file is distributed under the terms of the Software License Agreement found in the file LICENSE included with this distribution.

Author

M. Borland, R. Soliday

Definition in file pointInsideContour.c.

Function Documentation

pointIsInsideContour()

int pointIsInsideContour	(	double	x0,
		double	y0,
		double *	x,
		double *	y,
		int64_t	n,
		double *	center,
		double	theta )

Determine if a given point (x0, y0) is inside a specified polygonal contour.

This function uses the winding number method to check if the point (x0, y0) is inside the polygon defined by arrays x and y. If a rotation is specified (by a non-zero theta and a center), the point is rotated about the given center before the inside test is performed.

Parameters

[in]	x0	The x-coordinate of the point to test.
[in]	y0	The y-coordinate of the point to test.
[in]	x	Array of x-coordinates of the polygon vertices.
[in]	y	Array of y-coordinates of the polygon vertices.
[in]	n	The number of vertices in the polygon.
[in]	center	Pointer to an array representing the (x,y) center of rotation.
[in]	theta	The clockwise rotation angle (in radians) to apply to the polygon.

Returns

Non-zero if the point is inside the polygon, zero otherwise.

Definition at line 51 of file pointInsideContour.c.

  {
  int64_t winding_number = 0;
  int64_t i1, i2;
 
  if (theta != 0 && center) {
    double x1, y1, ct, st;
    /* rotate (x0, y0) by theta about center */
    x0 -= center[0];
    y0 -= center[1];
    ct = cos(theta);
    st = sin(theta);
    x1 = x0 * ct - y0 * st + center[0];
    y1 = x0 * st + y0 * ct + center[1];
    x0 = x1;
    y0 = y1;
  }
 
  for (i1 = 0; i1 < n; i1++) {
    if (i1 == (n - 1))
      /* wrap */
      i2 = 0;
    else
      i2 = i1 + 1;
 
    if (y[i1] <= y0) {
      /* start y <= y0 */
      if (y[i2] > y0) {
        /* upward crossing */
#ifdef DEBUG
        printf("upward crossing\n");
        fflush(stdout);
#endif
        if (pointIsLeftOfLine(i1, i2, x, y, x0, y0) > 0) {
          /* Point left of edge */
          ++winding_number;
        }
      }
    } else {
      /* start y > y0 */
      if (y[i2] <= y0) {
        /* downward crossing */
#ifdef DEBUG
        printf("downward crossing\n");
        fflush(stdout);
#endif
        if (pointIsLeftOfLine(i1, i2, x, y, x0, y0) < 0) {
          /* Point right of edge */
          --winding_number;
        }
      }
    }
#ifdef DEBUG
    printf("i1 = %" PRId64 ", winding_number = %" PRId64 "\n", i1, winding_number);
    fflush(stdout);
#endif
  }
 
#ifdef DEBUG
  printf("winding_number = %" PRId64 "\n", winding_number);
  fflush(stdout);
#endif
 
  return (winding_number != 0);
}

pointIsLeftOfLine()

double pointIsLeftOfLine	(	int64_t	i1,
		int64_t	i2,
		double *	x,
		double *	y,
		double	x0,
		double	y0 )

Definition at line 19 of file pointInsideContour.c.

  {
  double result;
  result = (x[i2] - x[i1]) * (y0 - y[i1]) - (x0 - x[i1]) * (y[i2] - y[i1]);
#ifdef DEBUG
  printf("pointIsLeftOfLine(%ld, %ld, %le, %le) = %le\n",
         i1, i2, x0, y0, result);
  fflush(stdout);
#endif
 
  return result;
}