PostGIS  3.1.6dev-r@@SVN_REVISION@@

◆ ptarray_locate_point()

double ptarray_locate_point ( const POINTARRAY pa,
const POINT4D p4d,
double *  mindistout,
POINT4D proj4d 
)

Definition at line 1311 of file ptarray.c.

1312 {
1313  double mindist=DBL_MAX;
1314  double tlen, plen;
1315  uint32_t t, seg=0;
1316  POINT4D start4d, end4d, projtmp;
1317  POINT2D proj, p;
1318  const POINT2D *start = NULL, *end = NULL;
1319 
1320  /* Initialize our 2D copy of the input parameter */
1321  p.x = p4d->x;
1322  p.y = p4d->y;
1323 
1324  if ( ! proj4d ) proj4d = &projtmp;
1325 
1326  /* Check for special cases (length 0 and 1) */
1327  if ( pa->npoints <= 1 )
1328  {
1329  if ( pa->npoints == 1 )
1330  {
1331  getPoint4d_p(pa, 0, proj4d);
1332  if ( mindistout )
1333  *mindistout = distance2d_pt_pt(&p, getPoint2d_cp(pa, 0));
1334  }
1335  return 0.0;
1336  }
1337 
1338  start = getPoint2d_cp(pa, 0);
1339  /* Loop through pointarray looking for nearest segment */
1340  for (t=1; t<pa->npoints; t++)
1341  {
1342  double dist_sqr;
1343  end = getPoint2d_cp(pa, t);
1344  dist_sqr = distance2d_sqr_pt_seg(&p, start, end);
1345 
1346  if (dist_sqr < mindist)
1347  {
1348  mindist = dist_sqr;
1349  seg=t-1;
1350  if ( mindist == 0 )
1351  {
1352  LWDEBUG(3, "Breaking on mindist=0");
1353  break;
1354  }
1355  }
1356 
1357  start = end;
1358  }
1359  mindist = sqrt(mindist);
1360 
1361  if ( mindistout ) *mindistout = mindist;
1362 
1363  LWDEBUGF(3, "Closest segment: %d", seg);
1364  LWDEBUGF(3, "mindist: %g", mindist);
1365 
1366  /*
1367  * We need to project the
1368  * point on the closest segment.
1369  */
1370  getPoint4d_p(pa, seg, &start4d);
1371  getPoint4d_p(pa, seg+1, &end4d);
1372  closest_point_on_segment(p4d, &start4d, &end4d, proj4d);
1373 
1374  /* Copy 4D values into 2D holder */
1375  proj.x = proj4d->x;
1376  proj.y = proj4d->y;
1377 
1378  LWDEBUGF(3, "Closest segment:%d, npoints:%d", seg, pa->npoints);
1379 
1380  /* For robustness, force 1 when closest point == endpoint */
1381  if ( (seg >= (pa->npoints-2)) && p2d_same(&proj, end) )
1382  {
1383  return 1.0;
1384  }
1385 
1386  LWDEBUGF(3, "Closest point on segment: %g,%g", proj.x, proj.y);
1387 
1388  tlen = ptarray_length_2d(pa);
1389 
1390  LWDEBUGF(3, "tlen %g", tlen);
1391 
1392  /* Location of any point on a zero-length line is 0 */
1393  /* See http://trac.osgeo.org/postgis/ticket/1772#comment:2 */
1394  if ( tlen == 0 ) return 0;
1395 
1396  plen=0;
1397  start = getPoint2d_cp(pa, 0);
1398  for (t=0; t<seg; t++, start=end)
1399  {
1400  end = getPoint2d_cp(pa, t+1);
1401  plen += distance2d_pt_pt(start, end);
1402 
1403  LWDEBUGF(4, "Segment %d made plen %g", t, plen);
1404  }
1405 
1406  plen+=distance2d_pt_pt(&proj, start);
1407 
1408  LWDEBUGF(3, "plen %g, tlen %g", plen, tlen);
1409 
1410  return plen/tlen;
1411 }
double distance2d_pt_pt(const POINT2D *p1, const POINT2D *p2)
Definition: measures.c:2397
int getPoint4d_p(const POINTARRAY *pa, uint32_t n, POINT4D *point)
Definition: lwgeom_api.c:126
double distance2d_sqr_pt_seg(const POINT2D *p, const POINT2D *A, const POINT2D *B)
Definition: measures.c:2407
int p2d_same(const POINT2D *p1, const POINT2D *p2)
Definition: lwalgorithm.c:50
#define LWDEBUG(level, msg)
Definition: lwgeom_log.h:83
#define LWDEBUGF(level, msg,...)
Definition: lwgeom_log.h:88
static const POINT2D * getPoint2d_cp(const POINTARRAY *pa, uint32_t n)
Returns a POINT2D pointer into the POINTARRAY serialized_ptlist, suitable for reading from.
Definition: lwinline.h:101
void closest_point_on_segment(const POINT4D *p, const POINT4D *A, const POINT4D *B, POINT4D *ret)
Definition: ptarray.c:1263
double ptarray_length_2d(const POINTARRAY *pts)
Find the 2d length of the given POINTARRAY (even if it's 3d)
Definition: ptarray.c:1757
double y
Definition: liblwgeom.h:404
double x
Definition: liblwgeom.h:404
double x
Definition: liblwgeom.h:428
double y
Definition: liblwgeom.h:428
uint32_t npoints
Definition: liblwgeom.h:441

References closest_point_on_segment(), distance2d_pt_pt(), distance2d_sqr_pt_seg(), getPoint2d_cp(), getPoint4d_p(), LWDEBUG, LWDEBUGF, POINTARRAY::npoints, p2d_same(), ptarray_length_2d(), POINT2D::x, POINT4D::x, POINT2D::y, and POINT4D::y.

Referenced by lwgeom_interpolate_point(), LWGEOM_line_locate_point(), and test_ptarray_locate_point().

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