[R-sig-Geo] converting SRTM data to filled contour plot

[Ian Harrison]

Hello,

I'm looking for advice on the best way to use NASA's SRTM data to produce a
filled contour plot. I've been tinkering with this over the past week or so, and
I think I'm almost there, but there are still a couple of roadblocks.

So far, I've been using a small, 7KB file of SRTM data that's in bil format.
Basically the commands that I run are:
x<-readGDAL('./44193054/44193054/44193054.bil')
contour(x, drawlabels=FALSE, col=1:5)

This produces a contour plot of the data, but there's still a couple of
problems: 1) The contours aren't filled. If I try filled.contour(), the function
complains about the format of x. I get the error "Non-numeric argument to
mathematical function". I haven't figured out how to extract the relevant data
from x and pass it to filled.contour(). 2) If I use a larger file, I quickly run
into memory problems. I haven't found the exact filesize where this occurs, but
I'd like to be able to use data files that are at least 80MB in size. Do I need
to break the files into smaller chunks, or is there another way?

So my questions are: 1) How can I create a filled contour plot of the data? 2)
How should I get around the memory problem? 

I'm an amateur with very little experience with the sp package or mapping in
general (but I do have experience with R), so I may be making some basic
mistakes. For example, I'm not sure I'm using the best data format, and I know
there are others available. I'm hoping that I'm trying to do something that's
very common and that there's an easy solution. Any help would be greatly
appreciated.

Thanks,
Ian