clipPolys {PBSmapping}

Clip a PolySet as Polygons

Description

Clip a PolySet, where each unique (PID, SID) describes a polygon.

Usage

clipPolys (polys, xlim, ylim, keepExtra = FALSE)

Arguments

polys

PolySet to clip.

xlim

range of X-coordinates.

ylim

range of Y-coordinates.

keepExtra

Boolean value; if TRUE, tries to carry forward any non-standard columns into the result.

Details

For each discrete polygon, the function connects vertices 1 and N. It recalculates the POS values for each vertex, saving the old values in a column named oldPOS. For new vertices, it sets oldPOS to NA.

Value

PolySet containing the input data, with some points added or removed. A new column oldPOS records the original POS value for each vertex.

Author(s)

Nicholas M. Boers, Staff Software Engineer
Jobber, Edmonton AB
Last modified Rd: 2013-04-10

See Also

clipLines, fixBound.

Examples

local(envir=.PBSmapEnv,expr={
  oldpar = par(no.readonly=TRUE)
  #--- create a triangle that will be clipped
  polys <- data.frame(PID=rep(1, 3), POS=1:3, X=c(0,1,.5), Y=c(0,0,1))
  #--- clip the triangle in the X direction, and plot the results
  plotPolys(clipPolys(polys,xlim=c(0,.75),ylim=range(polys[,"Y"])),col=2)
  par(oldpar)
})