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compassRose<-function(x,y,rot=0,cex=1) {
oldcex<-par(cex=cex)
mheight<-strheight("M")
xylim<-par("usr")
plotdim<-par("pin")
xmult<-(xylim[2]-xylim[1])/(xylim[4]-xylim[3])*plotdim[2]/plotdim[1]
point.angles<-seq(0,2*pi,by=pi/4)+pi*rot/180
crspans<-rep(c(mheight*3,mheight/2),length.out=9)
xpoints<-cos(point.angles)*crspans*xmult+x
ypoints<-sin(point.angles)*crspans+y
for(point in 1:8) {
pcol<-ifelse(point%%2,"black","white")
polygon(c(xpoints[c(point,point+1)],x),c(ypoints[c(point,point+1)],y),col=pcol)
}
txtxpoints<-cos(point.angles[c(1,3,5,7)])*1.2*crspans[1]*xmult+x
txtypoints<-sin(point.angles[c(1,3,5,7)])*1.2*crspans[1]+y
text(txtxpoints,txtypoints,c("E","N","W","S"))
par(oldcex)
}
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