PostGIS  2.1.10dev-r@@SVN_REVISION@@
LWLINE* lwline_measured_from_lwline ( const LWLINE lwline,
double  m_start,
double  m_end 
)

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

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

Definition at line 366 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().

367 {
368  int i = 0;
369  int hasm = 0, hasz = 0;
370  int npoints = 0;
371  double length = 0.0;
372  double length_so_far = 0.0;
373  double m_range = m_end - m_start;
374  double m;
375  POINTARRAY *pa = NULL;
376  POINT3DZ p1, p2;
377 
378  if ( lwline->type != LINETYPE )
379  {
380  lwerror("lwline_construct_from_lwline: only line types supported");
381  return NULL;
382  }
383 
384  hasz = FLAGS_GET_Z(lwline->flags);
385  hasm = 1;
386 
387  /* Null points or npoints == 0 will result in empty return geometry */
388  if ( lwline->points )
389  {
390  npoints = lwline->points->npoints;
391  length = ptarray_length_2d(lwline->points);
392  getPoint3dz_p(lwline->points, 0, &p1);
393  }
394 
395  pa = ptarray_construct(hasz, hasm, npoints);
396 
397  for ( i = 0; i < npoints; i++ )
398  {
399  POINT4D q;
400  POINT2D a, b;
401  getPoint3dz_p(lwline->points, i, &p2);
402  a.x = p1.x;
403  a.y = p1.y;
404  b.x = p2.x;
405  b.y = p2.y;
406  length_so_far += distance2d_pt_pt(&a, &b);
407  if ( length > 0.0 )
408  m = m_start + m_range * length_so_far / length;
409  else
410  m = 0.0;
411  q.x = p2.x;
412  q.y = p2.y;
413  q.z = p2.z;
414  q.m = m;
415  ptarray_set_point4d(pa, i, &q);
416  p1 = p2;
417  }
418 
419  return lwline_construct(lwline->srid, NULL, pa);
420 }
void ptarray_set_point4d(POINTARRAY *pa, int n, const POINT4D *p4d)
Definition: lwgeom_api.c:501
double x
Definition: liblwgeom.h:308
#define LINETYPE
Definition: liblwgeom.h:61
uint8_t type
Definition: liblwgeom.h:374
double z
Definition: liblwgeom.h:290
double y
Definition: liblwgeom.h:290
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:49
double m
Definition: liblwgeom.h:308
double x
Definition: liblwgeom.h:290
int npoints
Definition: liblwgeom.h:327
double ptarray_length_2d(const POINTARRAY *pts)
Find the 2d length of the given POINTARRAY (even if it's 3d)
Definition: ptarray.c:1586
double distance2d_pt_pt(const POINT2D *p1, const POINT2D *p2)
The old function nessecary for ptarray_segmentize2d in ptarray.c.
Definition: measures.c:2123
int32_t srid
Definition: liblwgeom.h:377
void lwerror(const char *fmt,...)
Write a notice out to the error handler.
Definition: lwutil.c:67
double x
Definition: liblwgeom.h:284
int getPoint3dz_p(const POINTARRAY *pa, int n, POINT3DZ *point)
Definition: lwgeom_api.c:305
double y
Definition: liblwgeom.h:284
#define FLAGS_GET_Z(flags)
Macros for manipulating the 'flags' byte.
Definition: liblwgeom.h:106
double z
Definition: liblwgeom.h:308
double y
Definition: liblwgeom.h:308
uint8_t flags
Definition: liblwgeom.h:375
LWLINE * lwline_construct(int srid, GBOX *bbox, POINTARRAY *points)
Definition: lwline.c:29
POINTARRAY * points
Definition: liblwgeom.h:378

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