*
*
* IDENTIFICATION
- * $PostgreSQL: pgsql/src/backend/utils/adt/geo_ops.c,v 1.95 2007/02/27 23:48:08 tgl Exp $
+ * $PostgreSQL: pgsql/src/backend/utils/adt/geo_ops.c,v 1.96 2007/03/05 23:29:14 momjian Exp $
*
*-------------------------------------------------------------------------
*/
***********************************************************************/
/*
- * Test to see if the point is inside the polygon.
- * Code adapted from integer-based routines in WN: A Server for the HTTP
+ * Test to see if the point is inside the polygon, returns 1/0, or 2 if
+ * the point is on the polygon.
+ * Code adapted but not copied from integer-based routines in WN: A
+ * Server for the HTTP
* version 1.15.1, file wn/image.c
- * GPL Copyright (C) 1995 by John Franks
* http://hopf.math.northwestern.edu/index.html
* Description of algorithm: http://www.linuxjournal.com/article/2197
+ * http://www.linuxjournal.com/article/2029
*/
-#define HIT_IT INT_MAX
+#define POINT_ON_POLYGON INT_MAX
static int
point_inside(Point *p, int npts, Point *plist)
{
double x0,
y0;
- double px,
- py;
- int i;
+ double prev_x,
+ prev_y;
+ int i = 0;
double x,
y;
- int cross,
- crossnum;
-
-/*
- * We calculate crossnum, which is twice the crossing number of a
- * ray from the origin parallel to the positive X axis.
- * A coordinate change is made to move the test point to the origin.
- * Then the function lseg_crossing() is called to calculate the crossnum of
- * one segment of the translated polygon with the ray which is the
- * positive X-axis.
- */
+ int cross, total_cross = 0;
- crossnum = 0;
- i = 0;
if (npts <= 0)
return 0;
+ /* compute first polygon point relative to single point */
x0 = plist[0].x - p->x;
y0 = plist[0].y - p->y;
- px = x0;
- py = y0;
+ prev_x = x0;
+ prev_y = y0;
+ /* loop over polygon points and aggregate total_cross */
for (i = 1; i < npts; i++)
{
+ /* compute next polygon point relative to single point */
x = plist[i].x - p->x;
y = plist[i].y - p->y;
- if ((cross = lseg_crossing(x, y, px, py)) == HIT_IT)
+ /* compute previous to current point crossing */
+ if ((cross = lseg_crossing(x, y, prev_x, prev_y)) == POINT_ON_POLYGON)
return 2;
- crossnum += cross;
-
- px = x;
- py = y;
+ total_cross += cross;
+
+ prev_x = x;
+ prev_y = y;
}
- if ((cross = lseg_crossing(x0, y0, px, py)) == HIT_IT)
+
+ /* now do the first point */
+ if ((cross = lseg_crossing(x0, y0, prev_x, prev_y)) == POINT_ON_POLYGON)
return 2;
- crossnum += cross;
- if (crossnum != 0)
+ total_cross += cross;
+
+ if (total_cross != 0)
return 1;
return 0;
}
/* lseg_crossing()
- * The function lseg_crossing() returns +2, or -2 if the segment from (x,y)
- * to previous (x,y) crosses the positive X-axis positively or negatively.
- * It returns +1 or -1 if one endpoint is on this ray, or 0 if both are.
- * It returns 0 if the ray and the segment don't intersect.
- * It returns HIT_IT if the segment contains (0,0)
+ * Returns +/-2 if line segment crosses the positive X-axis in a +/- direction.
+ * Returns +/-1 if one point is on the positive X-axis.
+ * Returns 0 if both points are on the positive X-axis, or there is no crossing.
+ * Returns POINT_ON_POLYGON if the segment contains (0,0).
+ * Wow, that is one confusing API, but it is used above, and when summed,
+ * can tell is if a point is in a polygon.
*/
static int
-lseg_crossing(double x, double y, double px, double py)
+lseg_crossing(double x, double y, double prev_x, double prev_y)
{
double z;
- int sgn;
-
- /* If (px,py) = (0,0) and not first call we have already sent HIT_IT */
+ int y_sign;
if (FPzero(y))
- {
- if (FPzero(x))
- {
- return HIT_IT;
-
- }
+ { /* y == 0, on X axis */
+ if (FPzero(x)) /* (x,y) is (0,0)? */
+ return POINT_ON_POLYGON;
else if (FPgt(x, 0))
- {
- if (FPzero(py))
- return FPgt(px, 0) ? 0 : HIT_IT;
- return FPlt(py, 0) ? 1 : -1;
-
+ { /* x > 0 */
+ if (FPzero(prev_y)) /* y and prev_y are zero */
+ /* prev_x > 0? */
+ return FPgt(prev_x, 0) ? 0 : POINT_ON_POLYGON;
+ return FPlt(prev_y, 0) ? 1 : -1;
}
else
- { /* x < 0 */
- if (FPzero(py))
- return FPlt(px, 0) ? 0 : HIT_IT;
+ { /* x < 0, x not on positive X axis */
+ if (FPzero(prev_y))
+ /* prev_x < 0? */
+ return FPlt(prev_x, 0) ? 0 : POINT_ON_POLYGON;
return 0;
}
}
-
- /* Now we know y != 0; set sgn to sign of y */
- sgn = (FPgt(y, 0) ? 1 : -1);
- if (FPzero(py))
- return FPlt(px, 0) ? 0 : sgn;
-
- if (FPgt((sgn * py), 0))
- { /* y and py have same sign */
- return 0;
-
- }
else
- { /* y and py have opposite signs */
- if (FPge(x, 0) && FPgt(px, 0))
- return 2 * sgn;
- if (FPlt(x, 0) && FPle(px, 0))
- return 0;
-
- z = (x - px) * y - (y - py) * x;
- if (FPzero(z))
- return HIT_IT;
- return FPgt((sgn * z), 0) ? 0 : 2 * sgn;
+ { /* y != 0 */
+ /* compute y crossing direction from previous point */
+ y_sign = FPgt(y, 0) ? 1 : -1;
+
+ if (FPzero(prev_y))
+ /* previous point was on X axis, so new point is either off or on */
+ return FPlt(prev_x, 0) ? 0 : y_sign;
+ else if (FPgt(y_sign * prev_y, 0))
+ /* both above or below X axis */
+ return 0; /* same sign */
+ else
+ { /* y and prev_y cross X-axis */
+ if (FPge(x, 0) && FPgt(prev_x, 0))
+ /* both non-negative so cross positive X-axis */
+ return 2 * y_sign;
+ if (FPlt(x, 0) && FPle(prev_x, 0))
+ /* both non-positive so do not cross positive X-axis */
+ return 0;
+
+ /* x and y cross axises, see URL above point_inside() */
+ z = (x - prev_x) * y - (y - prev_y) * x;
+ if (FPzero(z))
+ return POINT_ON_POLYGON;
+ return FPgt((y_sign * z), 0) ? 0 : 2 * y_sign;
+ }
}
}
projects / postgresql / commitdiff