point_in_ring()

static int point_in_ring ( POINTARRAY *  pts, const POINT2D *  point  )

static

Definition at line 778 of file lwgeom_functions_analytic.c.

{
        int wn = 0;
        uint32_t i;
        double side;
        const POINT2D* seg1;
        const POINT2D* seg2;
 
        POSTGIS_DEBUG(2, "point_in_ring called.");
 
        seg2 = getPoint2d_cp(pts, 0);
        for (i=0; i<pts->npoints-1; i++)
        {
                seg1 = seg2;
                seg2 = getPoint2d_cp(pts, i+1);
 
                side = determineSide(seg1, seg2, point);
 
                POSTGIS_DEBUGF(3, "segment: (%.8f, %.8f),(%.8f, %.8f)", seg1->x, seg1->y, seg2->x, seg2->y);
                POSTGIS_DEBUGF(3, "side result: %.8f", side);
                POSTGIS_DEBUGF(3, "counterclockwise wrap %d, clockwise wrap %d", FP_CONTAINS_BOTTOM(seg1->y, point->y, seg2->y), FP_CONTAINS_BOTTOM(seg2->y, point->y, seg1->y));
 
                /* zero length segments are ignored. */
                if ((seg2->x == seg1->x) && (seg2->y == seg1->y))
                {
                        POSTGIS_DEBUG(3, "segment is zero length... ignoring.");
 
                        continue;
                }
 
                /* a point on the boundary of a ring is not contained. */
                /* WAS: if (fabs(side) < 1e-12), see #852 */
                if (side == 0.0)
                {
                        if (isOnSegment(seg1, seg2, point) == 1)
                        {
                                POSTGIS_DEBUGF(3, "point on ring boundary between points %d, %d", i, i+1);
 
                                return 0;
                        }
                }
 
                /*
                 * If the point is to the left of the line, and it's rising,
                 * then the line is to the right of the point and
                 * circling counter-clockwise, so increment.
                 */
                if ((seg1->y <= point->y) && (point->y < seg2->y) && (side > 0))
                {
                        POSTGIS_DEBUG(3, "incrementing winding number.");
 
                        ++wn;
                }
                /*
                 * If the point is to the right of the line, and it's falling,
                 * then the line is to the right of the point and circling
                 * clockwise, so decrement.
                 */
                else if ((seg2->y <= point->y) && (point->y < seg1->y) && (side < 0))
                {
                        POSTGIS_DEBUG(3, "decrementing winding number.");
 
                        --wn;
                }
        }
 
        POSTGIS_DEBUGF(3, "winding number %d", wn);
 
        if (wn == 0)
                return -1;
        return 1;
}

References determineSide(), FP_CONTAINS_BOTTOM, getPoint2d_cp(), isOnSegment(), POINTARRAY::npoints, POINT2D::x, and POINT2D::y.

Referenced by point_in_multipolygon(), and point_in_polygon().

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