Dear listers,
I would like to write jpeg (or png, etc.) maps using the function
graphics:jpeg (png, etc.), but with the device window exactly fitting
the map (= no white strip above, below or on the sides of the map).
The map is derived from a SpatialPolygonsDataFrame (WGS84)
However, even if I set
par(mar=c(0,0,0,0) and pass xaxs='i', yaxs='i' in the plot, there are
still white strips
I tried several tricks but none are fully satisfying.
Trial #1: I computed the ratio of the bounding box and using this
ratio in the function jpeg with the height and width arguments. I did
it both in WGS84 and in UTM47:
ratio<-(max(bbox(ChinaUTM)[1,])-min(bbox(ChinaUTM)[1,]))/(max(bbox(ChinaUTM)[2,])-min(bbox(ChinaUTM)[2,]))
# ratio width/height
then
jpeg("./MapChina.jpeg",height=8,width=8*ratio,res=300,units="in")
par(mar=c(0,0,0,0)) # no margin
plot(China,col="grey",border="white",lwd=2,xaxs='i', yaxs='i')
dev.off()
The best is obtained with UTM47 (planar projection), however I get
(almost) rid of any white strip only if I add an additionnal 1.04
coefficient (obtained by trial-error)
Hence:
jpeg("./MapChina.jpeg",height=8,width=8*ratio*1.04,res=300,units="in")
par(mar=c(0,0,0,0)) # no margin
plot(China,col="grey",border="white",lwd=2,xaxs='i', yaxs='i')
dev.off()
Trial #2: The other way has been to pick up the parameter values like
that:
par(mar=c(0,0,0,0)) # no margin
plot(China,col="grey",border="white",lwd=2,xaxs='i', yaxs='i')
pt<-par()$pin
ratio<-pt[2]/pt[1]
jpeg("./MapChina.jpeg",height=8,width=8*ratio,res=300,units="in")
par(mar=c(0,0,0,0)) # no margin
plot(China,col="grey",border="white",lwd=2,xaxs='i', yaxs='i') #
dev.off()
Does not work either
Any idea about how to deal with this ? In short how to get the exact
size of a SpatialPolygonDataFrame plot to make the device window
exactly this? size?