maptools (version 0.8-21)

gpcholes: Hisaji Ono's lake/hole problem

Description

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.

Usage

data(gpcholes)

Arguments

source

Data file included in "gpclib" package.

Details

"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)*

Examples

Run this code
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)

Run the code above in your browser using DataCamp Workspace