PostGIS  2.5.0dev-r@@SVN_REVISION@@

◆ lwline_crossing_direction()

int lwline_crossing_direction ( const LWLINE l1,
const LWLINE l2 
)

lwline_crossing_direction: returns the kind of CG_LINE_CROSS_TYPE behavior of 2 linestrings

Given two lines, characterize how (and if) they cross each other.

Parameters
l1first line string
l2second line string
Returns
a CG_LINE_CROSS_TYPE LINE_NO_CROSS = 0 LINE_CROSS_LEFT = -1 LINE_CROSS_RIGHT = 1 LINE_MULTICROSS_END_LEFT = -2 LINE_MULTICROSS_END_RIGHT = 2 LINE_MULTICROSS_END_SAME_FIRST_LEFT = -3 LINE_MULTICROSS_END_SAME_FIRST_RIGHT = 3

Definition at line 460 of file lwalgorithm.c.

References getPoint2d_cp(), LINE_CROSS_LEFT, LINE_CROSS_RIGHT, LINE_MULTICROSS_END_LEFT, LINE_MULTICROSS_END_RIGHT, LINE_MULTICROSS_END_SAME_FIRST_LEFT, LINE_MULTICROSS_END_SAME_FIRST_RIGHT, LINE_NO_CROSS, lw_segment_intersects(), LWDEBUG, LWDEBUGF, lwfree(), lwgeom_to_ewkt(), POINTARRAY::npoints, LWLINE::points, SEG_COLINEAR, SEG_CROSS_LEFT, SEG_CROSS_RIGHT, POINT2D::x, and POINT2D::y.

Referenced by ST_LineCrossingDirection(), test_lwline_crossing_bugs(), test_lwline_crossing_long_lines(), and test_lwline_crossing_short_lines().

461 {
462  uint32_t i = 0, j = 0;
463  const POINT2D *p1, *p2, *q1, *q2;
464  POINTARRAY *pa1 = NULL, *pa2 = NULL;
465  int cross_left = 0;
466  int cross_right = 0;
467  int first_cross = 0;
468  int this_cross = 0;
469 #if POSTGIS_DEBUG_LEVEL >= 4
470  char *geom_ewkt;
471 #endif
472 
473  pa1 = (POINTARRAY*)l1->points;
474  pa2 = (POINTARRAY*)l2->points;
475 
476  /* One-point lines can't intersect (and shouldn't exist). */
477  if ( pa1->npoints < 2 || pa2->npoints < 2 )
478  return LINE_NO_CROSS;
479 
480 #if POSTGIS_DEBUG_LEVEL >= 4
481  geom_ewkt = lwgeom_to_ewkt((LWGEOM*)l1);
482  LWDEBUGF(4, "l1 = %s", geom_ewkt);
483  lwfree(geom_ewkt);
484  geom_ewkt = lwgeom_to_ewkt((LWGEOM*)l2);
485  LWDEBUGF(4, "l2 = %s", geom_ewkt);
486  lwfree(geom_ewkt);
487 #endif
488 
489  /* Initialize first point of q */
490  q1 = getPoint2d_cp(pa2, 0);
491 
492  for ( i = 1; i < pa2->npoints; i++ )
493  {
494 
495  /* Update second point of q to next value */
496  q2 = getPoint2d_cp(pa2, i);
497 
498  /* Initialize first point of p */
499  p1 = getPoint2d_cp(pa1, 0);
500 
501  for ( j = 1; j < pa1->npoints; j++ )
502  {
503 
504  /* Update second point of p to next value */
505  p2 = getPoint2d_cp(pa1, j);
506 
507  this_cross = lw_segment_intersects(p1, p2, q1, q2);
508 
509  LWDEBUGF(4, "i=%d, j=%d (%.8g %.8g, %.8g %.8g)", this_cross, i, j, p1->x, p1->y, p2->x, p2->y);
510 
511  if ( this_cross == SEG_CROSS_LEFT )
512  {
513  LWDEBUG(4,"this_cross == SEG_CROSS_LEFT");
514  cross_left++;
515  if ( ! first_cross )
516  first_cross = SEG_CROSS_LEFT;
517  }
518 
519  if ( this_cross == SEG_CROSS_RIGHT )
520  {
521  LWDEBUG(4,"this_cross == SEG_CROSS_RIGHT");
522  cross_right++;
523  if ( ! first_cross )
524  first_cross = SEG_CROSS_LEFT;
525  }
526 
527  /*
528  ** Crossing at a co-linearity can be turned handled by extending
529  ** segment to next vertex and seeing if the end points straddle
530  ** the co-linear segment.
531  */
532  if ( this_cross == SEG_COLINEAR )
533  {
534  LWDEBUG(4,"this_cross == SEG_COLINEAR");
535  /* TODO: Add logic here and in segment_intersects()
536  continue;
537  */
538  }
539 
540  LWDEBUG(4,"this_cross == SEG_NO_INTERSECTION");
541 
542  /* Turn second point of p into first point */
543  p1 = p2;
544 
545  }
546 
547  /* Turn second point of q into first point */
548  q1 = q2;
549 
550  }
551 
552  LWDEBUGF(4, "first_cross=%d, cross_left=%d, cross_right=%d", first_cross, cross_left, cross_right);
553 
554  if ( !cross_left && !cross_right )
555  return LINE_NO_CROSS;
556 
557  if ( !cross_left && cross_right == 1 )
558  return LINE_CROSS_RIGHT;
559 
560  if ( !cross_right && cross_left == 1 )
561  return LINE_CROSS_LEFT;
562 
563  if ( cross_left - cross_right == 1 )
565 
566  if ( cross_left - cross_right == -1 )
568 
569  if ( cross_left - cross_right == 0 && first_cross == SEG_CROSS_LEFT )
571 
572  if ( cross_left - cross_right == 0 && first_cross == SEG_CROSS_RIGHT )
574 
575  return LINE_NO_CROSS;
576 
577 }
void lwfree(void *mem)
Definition: lwutil.c:244
char * lwgeom_to_ewkt(const LWGEOM *lwgeom)
Return an alloced string.
Definition: lwgeom.c:556
#define LWDEBUG(level, msg)
Definition: lwgeom_log.h:83
int lw_segment_intersects(const POINT2D *p1, const POINT2D *p2, const POINT2D *q1, const POINT2D *q2)
returns the kind of CG_SEGMENT_INTERSECTION_TYPE behavior of lineseg 1 (constructed from p1 and p2) a...
Definition: lwalgorithm.c:371
unsigned int uint32_t
Definition: uthash.h:78
double x
Definition: liblwgeom.h:330
double y
Definition: liblwgeom.h:330
#define LWDEBUGF(level, msg,...)
Definition: lwgeom_log.h:88
const POINT2D * getPoint2d_cp(const POINTARRAY *pa, uint32_t n)
Returns a POINT2D pointer into the POINTARRAY serialized_ptlist, suitable for reading from...
Definition: lwgeom_api.c:364
POINTARRAY * points
Definition: liblwgeom.h:424
uint32_t npoints
Definition: liblwgeom.h:373
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