Function msIntersectionPointLine

maputil.c:1119–1166

/ IntersectionPointLinepointObj *p, pointObj *a, pointObj *b) */ / Retunrs a point object corresponding to the intersection of */ point p and a line formed of 2 points : a and b. */ / Alorith base on : */ http://www.faqs.org/faqs/graphics/algorithms-faq/ */ / Subject 1.02:How do I find the distance from a point to a

/*                                                                      */
/************************************************************************/
pointObj *msIntersectionPointLine(pointObj *p, pointObj *a, pointObj *b)
{
    double r = 0;
    double L = 0;
    pointObj *result = NULL;

    if (p && a && b)
    {
        L = sqrt(((b->x - a->x)*(b->x - a->x)) + 
                 ((b->y - a->y)*(b->y - a->y)));

        if (L != 0)
          r = ((p->x - a->x)*(b->x - a->x) + (p->y - a->y)*(b->y - a->y))/(L*L);
        else
          r = 0;

        result = (pointObj *)msSmallMalloc(sizeof(pointObj));
/* -------------------------------------------------------------------- */
/*      We want to make sure that the point returned is on the line     */
/*                                                                      */
/*              r=0      P = A                                          */
/*              r=1      P = B                                          */
/*              r<0      P is on the backward extension of AB           */
/*              r>1      P is on the forward extension of AB            */
/*                    0<r<1    P is interior to AB                      */
/* -------------------------------------------------------------------- */
        if (r < 0)
        {
            result->x = a->x;
            result->y = a->y;
        }
        else if (r > 1)
        {
            result->x = b->x;
            result->y = b->y;
        }
        else
        {
            result->x = a->x + r*(b->x - a->x);
            result->y = a->y + r*(b->y - a->y);
        }
#ifdef USE_POINT_Z_M
        result->m = 0;
#endif
    }

    return result;
}


/************************************************************************/