Clip a PolySet as Polygons
Clip a PolySet, where each unique (PID, SID) describes
a polygon.
clipPolys (polys, xlim, ylim, keepExtra = FALSE)
polys |
PolySet to clip. |
xlim |
range of X-coordinates. |
ylim |
range of Y-coordinates. |
keepExtra |
Boolean value; if |
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.
PolySet containing the input data, with some points added or
removed. A new column oldPOS records the original POS
value for each vertex.
Nicholas M. Boers, Associate Professor – Computer Science
MacEwan University, Edmonton AB
Last modified Rd: 2013-04-10
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)
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