PostGIS  2.5.1dev-r@@SVN_REVISION@@

◆ pt_continues_arc()

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 792 of file lwstroke.c.

References distance2d_pt_pt(), EPSILON_SQLMM, lw_arc_angle(), lw_arc_center(), LW_FALSE, lw_segment_side(), LW_TRUE, and LWDEBUGF.

Referenced by pta_unstroke().

793 {
794  POINT2D center;
795  POINT2D *t1 = (POINT2D*)a1;
796  POINT2D *t2 = (POINT2D*)a2;
797  POINT2D *t3 = (POINT2D*)a3;
798  POINT2D *tb = (POINT2D*)b;
799  double radius = lw_arc_center(t1, t2, t3, &center);
800  double b_distance, diff;
801 
802  /* Co-linear a1/a2/a3 */
803  if ( radius < 0.0 )
804  return LW_FALSE;
805 
806  b_distance = distance2d_pt_pt(tb, &center);
807  diff = fabs(radius - b_distance);
808  LWDEBUGF(4, "circle_radius=%g, b_distance=%g, diff=%g, percentage=%g", radius, b_distance, diff, diff/radius);
809 
810  /* Is the point b on the circle? */
811  if ( diff < EPSILON_SQLMM )
812  {
813  int a2_side = lw_segment_side(t1, t3, t2);
814  int b_side = lw_segment_side(t1, t3, tb);
815  double angle1 = lw_arc_angle(t1, t2, t3);
816  double angle2 = lw_arc_angle(t2, t3, tb);
817 
818  /* Is the angle similar to the previous one ? */
819  diff = fabs(angle1 - angle2);
820  LWDEBUGF(4, " angle1: %g, angle2: %g, diff:%g", angle1, angle2, diff);
821  if ( diff > EPSILON_SQLMM )
822  {
823  return LW_FALSE;
824  }
825 
826  /* Is the point b on the same side of a1/a3 as the mid-point a2 is? */
827  /* If not, it's in the unbounded part of the circle, so it continues the arc, return true. */
828  if ( b_side != a2_side )
829  return LW_TRUE;
830  }
831  return LW_FALSE;
832 }
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:228
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:770
double distance2d_pt_pt(const POINT2D *p1, const POINT2D *p2)
Definition: measures.c:2313
#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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