/*
 * v2d_line_distance.c - Calculate the distance between a point and a line
 *
 * Written 2012 by Werner Almesberger
 * Copyright 2012 Werner Almesberger
 *
 * This library is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Lesser General Public
 * License as published by the Free Software Foundation; either
 * version 2.1 of the License, or (at your option) any later version.
 */


#include <math.h>

#include "poly2d.h"


/*
 * We use formula (14) from
 * http://mathworld.wolfram.com/Point-LineDistance2-Dimensional.html
 * but keep the sign.
 */

double v2d_line_distance(const struct v2d *a, const struct v2d *b,
    const struct v2d *p)
{
	double ax, ay;

	ax = b->x-a->x;
	ay = b->y-a->y;

	return (ax*(a->y-p->y)-ay*(a->x-p->x))/hypot(ax, ay);
}