isIntersecting function

Determine Whether Polygons are Self-Intersecting

Determine whether polygons found in a PolySet are self-intersecting.

isIntersecting (polys, numericResult = FALSE)

Arguments

• polys: PolySet to use.
• numericResult: Boolean value; if TRUE, returns the number of intersections.

Details

When numericResult = TRUE, this function counts intersections as the algorithm processes them. It counts certain types (i.e., those involving vertices and those where an edge retraces over an edge) more than once.

The function does not give special consideration to holes. It returns a value for each unique (PID, SID), regardless of whether a contour represents a hole.

Returns

PolyData with columns PID, SID (may be missing), and intersecting. If numericResult is TRUE, intersecting contains the number of intersections. Otherwise, it contains a Boolean value.

Author(s)

Nicholas M. Boers, Staff Software Engineer

Jobber, Edmonton AB

Last modified Rd: 2013-04-10

See Also

isConvex, PolySet .

Examples

local(envir=.PBSmapEnv,expr={
  #--- load the data (if using R)
  if (!is.null(version$language) && (version$language=="R"))
  data(nepacLL,envir=.PBSmapEnv)
  #--- calculate then print the polygons that are self-intersecting
  p <- isIntersecting(nepacLL, numericResult = FALSE)
  print(p[p$intersecting,])
})