PostGIS  2.3.7dev-r@@SVN_REVISION@@
 static int pt_continues_arc ( const POINT4D * a1, const POINT4D * a2, const POINT4D * a3, const POINT4D * b )
static

Returns LW_TRUE if b is on the arc formed by a1/a2/a3, but not within that portion already described by a1/a2/a3.

Definition at line 518 of file lwstroke.c.

Referenced by pta_unstroke().

519 {
520  POINT2D center;
521  POINT2D *t1 = (POINT2D*)a1;
522  POINT2D *t2 = (POINT2D*)a2;
523  POINT2D *t3 = (POINT2D*)a3;
524  POINT2D *tb = (POINT2D*)b;
525  double radius = lw_arc_center(t1, t2, t3, &center);
526  double b_distance, diff;
527
528  /* Co-linear a1/a2/a3 */
529  if ( radius < 0.0 )
530  return LW_FALSE;
531
532  b_distance = distance2d_pt_pt(tb, &center);
533  diff = fabs(radius - b_distance);
535
536  /* Is the point b on the circle? */
537  if ( diff < EPSILON_SQLMM )
538  {
539  int a2_side = lw_segment_side(t1, t3, t2);
540  int b_side = lw_segment_side(t1, t3, tb);
541  double angle1 = lw_arc_angle(t1, t2, t3);
542  double angle2 = lw_arc_angle(t2, t3, tb);
543
544  /* Is the angle similar to the previous one ? */
545  diff = fabs(angle1 - angle2);
546  LWDEBUGF(4, " angle1: %g, angle2: %g, diff:%g", angle1, angle2, diff);
547  if ( diff > EPSILON_SQLMM )
548  {
549  return LW_FALSE;
550  }
551
552  /* Is the point b on the same side of a1/a3 as the mid-point a2 is? */
553  /* If not, it's in the unbounded part of the circle, so it continues the arc, return true. */
554  if ( b_side != a2_side )
555  return LW_TRUE;
556  }
557  return LW_FALSE;
558 }
double lw_arc_center(const POINT2D *p1, const POINT2D *p2, const POINT2D *p3, POINT2D *result)
Determines the center of the circle defined by the three given points.
Definition: lwalgorithm.c:227
static double lw_arc_angle(const POINT2D *a, const POINT2D *b, const POINT2D *c)
Return ABC angle in radians TODO: move to lwalgorithm.
Definition: lwstroke.c:496
double distance2d_pt_pt(const POINT2D *p1, const POINT2D *p2)
The old function nessecary for ptarray_segmentize2d in ptarray.c.
Definition: measures.c:2315
#define LW_FALSE
Definition: liblwgeom.h:76
#define EPSILON_SQLMM
Tolerance used to determine equality.
#define LW_TRUE
Return types for functions with status returns.
Definition: liblwgeom.h:75
int lw_segment_side(const POINT2D *p1, const POINT2D *p2, const POINT2D *q)
lw_segment_side()
Definition: lwalgorithm.c:64
#define LWDEBUGF(level, msg,...)
Definition: lwgeom_log.h:88

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