PostGIS  2.5.1dev-r@@SVN_REVISION@@

## ◆ distance2d_pt_seg()

 double distance2d_pt_seg ( const POINT2D * p, const POINT2D * A, const POINT2D * B )

Definition at line 2331 of file measures.c.

References distance2d_pt_pt(), FP_ABS, r, s, POINT2D::x, and POINT2D::y.

Referenced by lwline_split_by_point_to(), and ptarray_locate_point().

2332 {
2333  double r,s;
2334
2335  /*if start==end, then use pt distance */
2336  if ( ( A->x == B->x) && (A->y == B->y) )
2337  return distance2d_pt_pt(p,A);
2338
2339  /*
2340  * otherwise, we use comp.graphics.algorithms
2341  * Frequently Asked Questions method
2342  *
2343  * (1) AC dot AB
2344  * r = ---------
2345  * ||AB||^2
2346  * r has the following meaning:
2347  * r=0 P = A
2348  * r=1 P = B
2349  * r<0 P is on the backward extension of AB
2350  * r>1 P is on the forward extension of AB
2351  * 0<r<1 P is interior to AB
2352  */
2353
2354  r = ( (p->x-A->x) * (B->x-A->x) + (p->y-A->y) * (B->y-A->y) )/( (B->x-A->x)*(B->x-A->x) +(B->y-A->y)*(B->y-A->y) );
2355
2356  if (r<0) return distance2d_pt_pt(p,A);
2357  if (r>1) return distance2d_pt_pt(p,B);
2358
2359
2360  /*
2361  * (2)
2362  * (Ay-Cy)(Bx-Ax)-(Ax-Cx)(By-Ay)
2363  * s = -----------------------------
2364  * L^2
2365  *
2366  * Then the distance from C to P = |s|*L.
2367  *
2368  */
2369
2370  s = ( (A->y-p->y)*(B->x-A->x)- (A->x-p->x)*(B->y-A->y) ) /
2371  ( (B->x-A->x)*(B->x-A->x) +(B->y-A->y)*(B->y-A->y) );
2372
2373  return FP_ABS(s) * sqrt(
2374  (B->x-A->x)*(B->x-A->x) + (B->y-A->y)*(B->y-A->y)
2375  );
2376 }
char * r
Definition: cu_in_wkt.c:24
double x
Definition: liblwgeom.h:330
double y
Definition: liblwgeom.h:330
char * s
Definition: cu_in_wkt.c:23
double distance2d_pt_pt(const POINT2D *p1, const POINT2D *p2)
Definition: measures.c:2313
#define FP_ABS(a)
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