PostGIS  2.5.0dev-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 779 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().

780 {
781  POINT2D center;
782  POINT2D *t1 = (POINT2D*)a1;
783  POINT2D *t2 = (POINT2D*)a2;
784  POINT2D *t3 = (POINT2D*)a3;
785  POINT2D *tb = (POINT2D*)b;
786  double radius = lw_arc_center(t1, t2, t3, &center);
787  double b_distance, diff;
788 
789  /* Co-linear a1/a2/a3 */
790  if ( radius < 0.0 )
791  return LW_FALSE;
792 
793  b_distance = distance2d_pt_pt(tb, &center);
794  diff = fabs(radius - b_distance);
795  LWDEBUGF(4, "circle_radius=%g, b_distance=%g, diff=%g, percentage=%g", radius, b_distance, diff, diff/radius);
796 
797  /* Is the point b on the circle? */
798  if ( diff < EPSILON_SQLMM )
799  {
800  int a2_side = lw_segment_side(t1, t3, t2);
801  int b_side = lw_segment_side(t1, t3, tb);
802  double angle1 = lw_arc_angle(t1, t2, t3);
803  double angle2 = lw_arc_angle(t2, t3, tb);
804 
805  /* Is the angle similar to the previous one ? */
806  diff = fabs(angle1 - angle2);
807  LWDEBUGF(4, " angle1: %g, angle2: %g, diff:%g", angle1, angle2, diff);
808  if ( diff > EPSILON_SQLMM )
809  {
810  return LW_FALSE;
811  }
812 
813  /* Is the point b on the same side of a1/a3 as the mid-point a2 is? */
814  /* If not, it's in the unbounded part of the circle, so it continues the arc, return true. */
815  if ( b_side != a2_side )
816  return LW_TRUE;
817  }
818  return LW_FALSE;
819 }
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:757
double distance2d_pt_pt(const POINT2D *p1, const POINT2D *p2)
Definition: measures.c:2312
#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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