PostGIS  2.5.1dev-r@@SVN_REVISION@@

◆ lwline_measured_from_lwline()

LWLINE* lwline_measured_from_lwline ( const LWLINE lwline,
double  m_start,
double  m_end 
)

Re-write the measure ordinate (or add one, if it isn't already there) interpolating the measure between the supplied start and end values.

Add a measure dimension to a line, interpolating linearly from the start to the end value.

Definition at line 388 of file lwline.c.

References distance2d_pt_pt(), LWLINE::flags, FLAGS_GET_Z, getPoint3dz_p(), LINETYPE, lwerror(), lwline_construct(), POINT4D::m, POINTARRAY::npoints, LWLINE::points, ptarray_construct(), ptarray_length_2d(), ptarray_set_point4d(), LWLINE::srid, LWLINE::type, POINT2D::x, POINT3DZ::x, POINT4D::x, POINT2D::y, POINT3DZ::y, POINT4D::y, POINT3DZ::z, and POINT4D::z.

Referenced by lwline_locate_along(), lwmline_measured_from_lwmline(), and ST_AddMeasure().

389 {
390  int i = 0;
391  int hasm = 0, hasz = 0;
392  int npoints = 0;
393  double length = 0.0;
394  double length_so_far = 0.0;
395  double m_range = m_end - m_start;
396  double m;
397  POINTARRAY *pa = NULL;
398  POINT3DZ p1, p2;
399 
400  if ( lwline->type != LINETYPE )
401  {
402  lwerror("lwline_construct_from_lwline: only line types supported");
403  return NULL;
404  }
405 
406  hasz = FLAGS_GET_Z(lwline->flags);
407  hasm = 1;
408 
409  /* Null points or npoints == 0 will result in empty return geometry */
410  if ( lwline->points )
411  {
412  npoints = lwline->points->npoints;
413  length = ptarray_length_2d(lwline->points);
414  getPoint3dz_p(lwline->points, 0, &p1);
415  }
416 
417  pa = ptarray_construct(hasz, hasm, npoints);
418 
419  for ( i = 0; i < npoints; i++ )
420  {
421  POINT4D q;
422  POINT2D a, b;
423  getPoint3dz_p(lwline->points, i, &p2);
424  a.x = p1.x;
425  a.y = p1.y;
426  b.x = p2.x;
427  b.y = p2.y;
428  length_so_far += distance2d_pt_pt(&a, &b);
429  if ( length > 0.0 )
430  m = m_start + m_range * length_so_far / length;
431  /* #3172, support (valid) zero-length inputs */
432  else if ( length == 0.0 && npoints > 1 )
433  m = m_start + m_range * i / (npoints-1);
434  else
435  m = 0.0;
436  q.x = p2.x;
437  q.y = p2.y;
438  q.z = p2.z;
439  q.m = m;
440  ptarray_set_point4d(pa, i, &q);
441  p1 = p2;
442  }
443 
444  return lwline_construct(lwline->srid, NULL, pa);
445 }
double x
Definition: liblwgeom.h:354
#define LINETYPE
Definition: liblwgeom.h:85
uint8_t type
Definition: liblwgeom.h:420
double z
Definition: liblwgeom.h:336
double y
Definition: liblwgeom.h:336
POINTARRAY * ptarray_construct(char hasz, char hasm, uint32_t npoints)
Construct an empty pointarray, allocating storage and setting the npoints, but not filling in any inf...
Definition: ptarray.c:62
double m
Definition: liblwgeom.h:354
double x
Definition: liblwgeom.h:336
double ptarray_length_2d(const POINTARRAY *pts)
Find the 2d length of the given POINTARRAY (even if it&#39;s 3d)
Definition: ptarray.c:1689
void ptarray_set_point4d(POINTARRAY *pa, uint32_t n, const POINT4D *p4d)
Definition: lwgeom_api.c:425
double distance2d_pt_pt(const POINT2D *p1, const POINT2D *p2)
Definition: measures.c:2313
int32_t srid
Definition: liblwgeom.h:423
double x
Definition: liblwgeom.h:330
double y
Definition: liblwgeom.h:330
#define FLAGS_GET_Z(flags)
Macros for manipulating the &#39;flags&#39; byte.
Definition: liblwgeom.h:139
double z
Definition: liblwgeom.h:354
int getPoint3dz_p(const POINTARRAY *pa, uint32_t n, POINT3DZ *point)
Definition: lwgeom_api.c:205
double y
Definition: liblwgeom.h:354
uint8_t flags
Definition: liblwgeom.h:421
void lwerror(const char *fmt,...)
Write a notice out to the error handler.
Definition: lwutil.c:190
LWLINE * lwline_construct(int srid, GBOX *bbox, POINTARRAY *points)
Definition: lwline.c:42
POINTARRAY * points
Definition: liblwgeom.h:424
uint32_t npoints
Definition: liblwgeom.h:373
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