[GRASS-user] Very high resolution topographic map of Europe: need help and advices

[Felix Schalck]

Hello,

For some time now, I'm following sort of a personal objective to
create the most precise (=high resolution) topographic map of Europe
allowed by my comp (Xubuntu 9.04, AMD64, 3Gb RAM, 300+ HD space).
Starting from the very scratch, I had to learn about DEMs and
GIS/maptools - and I'm still not confortable with all the technicy
behind. Fact is that the best data set available to serve my purpose
seems to be the cgiar interpolated srtm3 geodata (no license problem
here, since it is aimed for pure personal use) which has to somehow be
translated into a big jpeg or png file.

I started with GMT, and tried to render the whole aera between 34N and
60N, 11W and 35E with grdimage into a 6000x8000 pix [I made slices of
3°x46°, which I pasted together]. Given the amount of data, GMT softs
take forever, but it seems to be the fate of this project to hit the
limits of my hardware... The big problem happened to be the river
data, since GSHHS provides only limited amount and precision of
side-rivers, which resulted in chains of straight lines scattered all
over a giant map, even after vectorization: it was a no-go.

And then, a few days ago, I discovered nasa SWBD data and WMAP0, which
seem to be of much higher resolution, linked to a nice GRASS GIS
tutorial on the french wikipedia. I immedialely dug into this new
software, quite complicated I must admit, but very powerful. I figured
out how to import GeoTiff data into GRASS Raster files, and how to
display/export each one of them, but soon had to face new problems,
especially when tried to reproject the data into LCC projection. So I
decided to ask for help on this mailing list.

My Current plan is to:
1. reproject the cgiar raster tiles OR one big merged raster into LCC
projection (native srtm data seems to be a strange Mercator)
2. create elevation shadings
3. export a nice shaded topographic png
4. extract rivers/coast vectors from SWBD files
5. workout in Inkscape
6. paste the whole thing together in GIMP.

The main problem right now seems to be the "tiling" of the topographic
data. Each cgiar-cell (5°x5°) can be shown into a separate layer, but
I'm unable to work them together. And it looks like most of the tools
provided by GRASS assume the raster map is the size of the location
(r.proj for an example). I tried r.patch but it produce wired results
on top of giant files (I stopped when I hit the 2Gb limit), perhaps
because the cgiar tiles do not exactly match my region (11W 35E 60N
34N). Is there a way to cut-off the overlapping tiles ? And than I'm
not sure the r.patch way is the right one, since the single resulting
file will become really big.

I took the time to explain the whole thing with the hope to not only
get help about my immediate raster division problem, but also about
the "big-picture", eg: is GRASS the right tools to do this (I
installed GRASS because of the SWBD data tutorial, but it seems to me
that swbd could also be plotted via psxy in GMT )? How would you
GIS-gurus proceed to create a high resolution topographic map ? Is one
big png a good idea, or would it be smarter to divide the continent
into 4 or more parts, and render each one into a separate png ?

Thanks you very much for your time,

Felix Schalck