Hello list
I am trying to use a Googlemaps tile (png file, 640 X 640 px tile) as a
background to a plot and have been using the rgdal library to read in the PNG
file (modified from code in the RGoogleMaps package). This works OK. My
problem is is that the SGDF2PCT function in rgdal seems to be limited to 256
colors and this is introducing (I think) some degradation to the image which
appears on the output graph as speckling.
Is there a way around this? I have been reading about the EBImage package but
it (a) seemed to have too many dependencies on other software for my purposes
and (b) wouldn't load properly in any case on my machine (couldn't find dll's
that it was looking for....)
Ideally I would like to read in the png image and display in its original form
as a plot background, hopefully with all its colors represented rather than
being converted to a 256 color scale.
A code example is below:
png(file="file.png", 4000,4000)
par(mar=c(0,0,0,0))
myTile <- readGDAL("basemap.png",silent=TRUE); #basemap.png is a PNG file
returned from googlemaps
myt...@data <- myt...@data[,1:3]
col <- SGDF2PCT(myTile,ncolors=256) ## myTile is a spatialGridDataFrame with
3 bands
myTile$ind <- col$idx ## add the colour index to the data frame
myTile <- as.image.SpatialGridDataFrame(myTile["ind"],1,2)$z;
attr(myTile, "COL") <- col$ct;
attr(myTile, "type") <- "rgb";
myTile <- list(lat.center, lon.center,NA, myTile)
image(z=myTile[[4]], col = attr(myTile[[4]], "COL"))
dev.off()
> sessionInfo()
R version 2.9.1 (2009-06-26)
i386-pc-mingw32
locale:
LC_COLLATE=English_Australia.1252;LC_CTYPE=English_Australia.1252;LC_MONETARY=English_Australia.1252;LC_NUMERIC=C;LC_TIME=English_Australia.1252
attached base packages:
[1] grid stats graphics grDevices utils datasets methods base
other attached packages:
[1] abind_1.1-0 rgdal_0.6-9 sp_0.9-37 gridBase_0.4-3
loaded via a namespace (and not attached):
[1] lattice_0.17-25 tools_2.9.1
Paul Rustomji
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