#include <grass/gis.h>
/* compute square of distance of point (x,y) to line segment (x1,y1 - x2,y2) */

#define ZERO(x) x < tolerance && x > -tolerance
#define TOLERANCE 1.0e-10
static double tolerance = TOLERANCE;

int G_set_distance_to_line_tolerance (double t)
{
    if (t <= 0.0)
	t = TOLERANCE;
    tolerance = t;

    return 0;
}

double G_distance2_point_to_line (
    double x,double y,         /* point */
    double x1,double y1,double x2,double y2)	/* line segment */
{
    double dx,dy,t;

    dx = x2 - x1;
    dy = y2 - y1;

    if (ZERO(dx) && ZERO(dy)) /* line is degenerate */
    {
	dx = x1 - x;
	dy = y1 - y;
	return dx*dx + dy*dy;	/* compute distance x,y to x1,y1 */
    }

    t = (dx * (x - x1) + dy * (y - y1)) / (dx * dx + dy * dy);

    if (t < 0.0)		/* go to x1,y1 */
    {
	dx = x - x1;
	dy = y - y1;
    }
    else if (t > 1.0)		/* go to x2,y2 */
    {
	dx = x - x2;
	dy = y - y2;
    }
    else                        /* go t from x1,y1 towards x2,y2 */
    {
	dx = x - (dx * t + x1);
	dy = y - (dy * t + y1);
    }
    return dx*dx + dy*dy;
}