Hisaji Ono's lake/hole problem
How to plot polygons with holes - holes are encoded by coordinates going anticlockwise, and overplotting is avoided by re-ordering the order in which polygons are plotted.
This example is retained for historical interest only, other solutions are present in the sp package.
"Date: Tue, 11 May 2004 12:54:20 +0900 From: Hisaji ONO To: r-help
I've tried to create a polygon with one hole by gpclib using following example script.
holepoly <- read.polyfile(system.file("poly-ex/hole-poly.txt", package="gpclib"), nohole = FALSE) area.poly(holepoly) plot(holepoly,poly.args=list(col="red",border="blue"))
And I noticed plot function couldn't draw polygons with holes correctly.
Does anyone know how to solve this situation?"
*(h1pl has reversed the y component of polygon 1, to make its ring direction clockwise, h2pl reverses the order of the two polygons in holepoly1@pts)*
Data file included in "gpclib" package.
data(gpcholes) opar <- par(mfrow=c(1,2)) plot(SpatialPolygons(list(h2pl)), col="red", pbg="white", border="blue") plot(SpatialPolygons(list(h1pl)), col="red", pbg="white", border="blue") par(opar)