On Sat, 27 Jul 2019, Patrick Giraudoux wrote:
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?
This feels like a section in ASDAR, ch. 3, and code chunks 24-27 in
https://asdar-book.org/book2ed/vis_mod.R. Could you please try that first
by way of something reproducible?
Best wishes,
Roger
Best,
Patrick
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--
Roger Bivand
Department of Economics, Norwegian School of Economics,
Helleveien 30, N-5045 Bergen, Norway.
voice: +47 55 95 93 55; e-mail: roger.biv...@nhh.no
https://orcid.org/0000-0003-2392-6140
https://scholar.google.no/citations?user=AWeghB0AAAAJ&hl=en
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