[R] how to plot image() without painting a map (the background)

[Rob Robinson]

I've used a similar three-stage approach. Depending on the format of your
map (mine came from an ArcView shape file) you may be able to specify
col="transparent" for the foreground (ie land) in plot as I did (tip, use
border= to get colours for the country borders). This works where alpha
channels don't, such as png. 
Not sure what image you have, but there may be alternatives, for example, I
found .Internal(filledcontour()) extremely useful because then I could
explicitly set some of the image to "transparent"...
Hth
rob

*** Want to know about Britain's birds? Try  www.bto.org/birdfacts ***

Dr Rob Robinson, Senior Population Biologist
British Trust for Ornithology, The Nunnery, Thetford, Norfolk, IP24 2PU
Ph: +44 (0)1842 750050         E: rob.robinson at bto.org
Fx: +44 (0)1842 750030         W: http://www.bto.org

==== "How can anyone be enlightened, when truth is so poorly lit" =====
  

> -----Original Message-----
> From: r-help-bounces at r-project.org 
> [mailto:r-help-bounces at r-project.org] On Behalf Of Greg Snow
> Sent: 19 February 2008 17:20
> To: Ptit_Bleu; r-help at r-project.org
> Subject: Re: [R] how to plot image() without painting a map 
> (the background)
> 
> The approach that I usually use for things like this is:
> 
> Plot the map to get the aspect ratio and limits correct.
> Add the image (obscuring the original map).
> Add the map again on top of the image using a light grey color.
> 
> This seems to work fine for me.  Another aproach that you may 
> try (untested) is to use colors with an alpha channel 
> (transparency) in the call to image, then the background map 
> may show through.  Not all graphics devices support alpha 
> channels, so test on one that does.
> 
> Hope this helps,
> 
> --
> Gregory (Greg) L. Snow Ph.D.
> Statistical Data Center
> Intermountain Healthcare
> greg.snow at imail.org
> (801) 408-8111
>  
>  
> 
> > -----Original Message-----
> > From: r-help-bounces at r-project.org
> > [mailto:r-help-bounces at r-project.org] On Behalf Of Ptit_Bleu
> > Sent: Monday, February 18, 2008 8:59 AM
> > To: r-help at r-project.org
> > Subject: [R] how to plot image() without painting a map (the
> > background)
> > 
> > 
> > Hello,
> > 
> > I'm trying to plot dayly evolution of the temperature over 
> France from 
> > Global Forecast System files ("I'm trying" is the right 
> > expression...).
> > 
> > akilonlat03 is the temperature for different latitudes and 
> longitudes 
> > à 3 o'clock.
> > akilonlat06 is the temperature for different latitudes and 
> longitudes 
> > à 6 o'clock.
> > 
> > I would like to plot akilonlat03 and then akilonlat06 and 
> keep the map 
> > of France in background.
> > My script (see below) doesn't work as image "paints" the 
> background as 
> > I read somewhere in this forum.
> > 
> > So would have someone a solution to correct my script ?
> > Thanks in advance,
> > Ptit Bleu.
> > 
> > ----------------------------------------------------
> > 
> > 
> > akilonlat03<-interp(lonlat03$Longitude, lonlat03$Latitude,
> > (5/9)*(lonlat03$TMP_200802150300-32))
> > akilonlat06<-interp(lonlat06$Longitude, lonlat06$Latitude,
> > (5/9)*(lonlat06$TMP_200802150600-32))
> > 
> > map('france')
> > 
> > image(akilonlat03, col=cm.colors(100), axes=FALSE, add=TRUE) 
> > #contour(akilonlat03, col="blue", add=TRUE) image(akilonlat06, 
> > col=cm.colors(100), axes=FALSE, add=TRUE) #contour(akilonlat06, 
> > col="blue", add=TRUE)
> > 
> > --
> > View this message in context: 
> > http://www.nabble.com/how-to-plot-image%28%29-without-painting
> > -a-map-%28the-background%29-tp15546906p15546906.html
> > Sent from the R help mailing list archive at Nabble.com.
> > 
> > ______________________________________________
> > R-help at r-project.org mailing list
> > https://stat.ethz.ch/mailman/listinfo/r-help
> > PLEASE do read the posting guide
> > http://www.R-project.org/posting-guide.html
> > and provide commented, minimal, self-contained, reproducible code.
> > 
> 
> ______________________________________________
> R-help at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide 
> http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
>