PostGIS  2.3.8dev-r@@SVN_REVISION@@

◆ closest_point_on_segment()

void closest_point_on_segment ( const POINT4D p,
const POINT4D A,
const POINT4D B,
POINT4D ret 
)

Definition at line 1262 of file ptarray.c.

References FP_EQUALS, POINT4D::m, r, POINT4D::x, POINT4D::y, and POINT4D::z.

Referenced by lwline_split_by_point_to(), and ptarray_locate_point().

1263 {
1264  double r;
1265 
1266  if ( FP_EQUALS(A->x, B->x) && FP_EQUALS(A->y, B->y) )
1267  {
1268  *ret = *A;
1269  return;
1270  }
1271 
1272  /*
1273  * We use comp.graphics.algorithms Frequently Asked Questions method
1274  *
1275  * (1) AC dot AB
1276  * r = ----------
1277  * ||AB||^2
1278  * r has the following meaning:
1279  * r=0 P = A
1280  * r=1 P = B
1281  * r<0 P is on the backward extension of AB
1282  * r>1 P is on the forward extension of AB
1283  * 0<r<1 P is interior to AB
1284  *
1285  */
1286  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) );
1287 
1288  if (r<0)
1289  {
1290  *ret = *A;
1291  return;
1292  }
1293  if (r>1)
1294  {
1295  *ret = *B;
1296  return;
1297  }
1298 
1299  ret->x = A->x + ( (B->x - A->x) * r );
1300  ret->y = A->y + ( (B->y - A->y) * r );
1301  ret->z = A->z + ( (B->z - A->z) * r );
1302  ret->m = A->m + ( (B->m - A->m) * r );
1303 }
double x
Definition: liblwgeom.h:351
double m
Definition: liblwgeom.h:351
char * r
Definition: cu_in_wkt.c:24
double z
Definition: liblwgeom.h:351
#define FP_EQUALS(A, B)
double y
Definition: liblwgeom.h:351
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