PostGIS  2.5.0dev-r@@SVN_REVISION@@
double distance2d_pt_seg ( const POINT2D p,
const POINT2D A,
const POINT2D B 
)

The old function nessecary for ptarray_segmentize2d in ptarray.c.

Definition at line 2337 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().

2338 {
2339  double r,s;
2340 
2341  /*if start==end, then use pt distance */
2342  if ( ( A->x == B->x) && (A->y == B->y) )
2343  return distance2d_pt_pt(p,A);
2344 
2345  /*
2346  * otherwise, we use comp.graphics.algorithms
2347  * Frequently Asked Questions method
2348  *
2349  * (1) AC dot AB
2350  * r = ---------
2351  * ||AB||^2
2352  * r has the following meaning:
2353  * r=0 P = A
2354  * r=1 P = B
2355  * r<0 P is on the backward extension of AB
2356  * r>1 P is on the forward extension of AB
2357  * 0<r<1 P is interior to AB
2358  */
2359 
2360  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) );
2361 
2362  if (r<0) return distance2d_pt_pt(p,A);
2363  if (r>1) return distance2d_pt_pt(p,B);
2364 
2365 
2366  /*
2367  * (2)
2368  * (Ay-Cy)(Bx-Ax)-(Ax-Cx)(By-Ay)
2369  * s = -----------------------------
2370  * L^2
2371  *
2372  * Then the distance from C to P = |s|*L.
2373  *
2374  */
2375 
2376  s = ( (A->y-p->y)*(B->x-A->x)- (A->x-p->x)*(B->y-A->y) ) /
2377  ( (B->x-A->x)*(B->x-A->x) +(B->y-A->y)*(B->y-A->y) );
2378 
2379  return FP_ABS(s) * sqrt(
2380  (B->x-A->x)*(B->x-A->x) + (B->y-A->y)*(B->y-A->y)
2381  );
2382 }
char * r
Definition: cu_in_wkt.c:24
double x
Definition: liblwgeom.h:327
double y
Definition: liblwgeom.h:327
char * s
Definition: cu_in_wkt.c:23
double distance2d_pt_pt(const POINT2D *p1, const POINT2D *p2)
The old function nessecary for ptarray_segmentize2d in ptarray.c.
Definition: measures.c:2312
#define FP_ABS(a)

Here is the call graph for this function:

Here is the caller graph for this function: