PostGIS  2.3.7dev-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 2340 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().

2341 {
2342  double r,s;
2343 
2344  /*if start==end, then use pt distance */
2345  if ( ( A->x == B->x) && (A->y == B->y) )
2346  return distance2d_pt_pt(p,A);
2347 
2348  /*
2349  * otherwise, we use comp.graphics.algorithms
2350  * Frequently Asked Questions method
2351  *
2352  * (1) AC dot AB
2353  * r = ---------
2354  * ||AB||^2
2355  * r has the following meaning:
2356  * r=0 P = A
2357  * r=1 P = B
2358  * r<0 P is on the backward extension of AB
2359  * r>1 P is on the forward extension of AB
2360  * 0<r<1 P is interior to AB
2361  */
2362 
2363  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) );
2364 
2365  if (r<0) return distance2d_pt_pt(p,A);
2366  if (r>1) return distance2d_pt_pt(p,B);
2367 
2368 
2369  /*
2370  * (2)
2371  * (Ay-Cy)(Bx-Ax)-(Ax-Cx)(By-Ay)
2372  * s = -----------------------------
2373  * L^2
2374  *
2375  * Then the distance from C to P = |s|*L.
2376  *
2377  */
2378 
2379  s = ( (A->y-p->y)*(B->x-A->x)- (A->x-p->x)*(B->y-A->y) ) /
2380  ( (B->x-A->x)*(B->x-A->x) +(B->y-A->y)*(B->y-A->y) );
2381 
2382  return FP_ABS(s) * sqrt(
2383  (B->x-A->x)*(B->x-A->x) + (B->y-A->y)*(B->y-A->y)
2384  );
2385 }
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:2315
#define FP_ABS(a)

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