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

[Felix Schalck]

Dear Markus and other Grass users,

Here comes the latest update about my high resolution topographic map
of Europe - as usual - with some new questions.

Part1 (pasting cgiar-srtm tiles together) was a real pain, since I
needed to recompile GDAL with BigTIFF support in GTiFF driver to be
able to create such large geotiff files. Of course, once new gdal
successfully installed, I had to recompile GRASS against the new
gdal-bigtiff...
As posted on the gdal-dev mailing list, strange things occured during
my various gdalwarp attemps: while pasting all tiles bewteen
{34N;60N;-11W;35E} together in one command takes about 20h, dividing
the job in:
a - first merge "slices" of saying all tiles located in one long. column
b - finally paste all "slices" together
reduces the time needed to complete the command to around 4-5h. (I
posted 1 hour completion-time in the gdal list, but it was on a
smaller region)

Part2 has been updated to import the geotiff file in a lat/long
projection location native to srtm data, and than reproject the
obtained raster into my selected lcc (lambert conical conformal)
projection. This was probably the longest part, since it took r.proj
about 8h to complete this task. It tooks me actually twice as long,
since my region bounds were not properly set to include the distortion
of the lcc projection, so that the first re-projected raster had been
cut off just over Denmark; and I had to launch the reprojection
again...

Part3 is about creating the shadings, still ongoing, and works
surprinsingly well with r.shaded.relief, tough I'm still messing
around with zmult and azimut options to get the desired shadings.
Should somebody have advices here, to get nice shadings for large
srtm-based topographic maps, feel free to post them.
@Markus: I did not try the gdaldem tool to create the shadings, since
I re-projected the DEM in GRASS raster format.

Part4 is were I'm stuck currently, and is about creating coastline
vectors, bathymetry and exporting the results to be re-worked/merged
in GIMP.
a - Importing the vectors from SWBD is no problem, tough It would be
nice to have the 200+ NASA shapefiles merged BEFORE importing a new
layer in GRASS. Is this possible with ogr2ogr ?
b - The big problem are coastlines and waterbodies (+main rivers):
somehow I have to show them on the topographic map, which gdalwarp has
filled out with -32768 values in nodata-waterzones. So either I cut
waterbodies out of the topographic raster along the vectors, or I
somehow have GRASS compute me all waterbodies from the vector layer,
fill them with a nice blue and create a raster which can be pasted
over the topographic raster to get the final map.  It seems doable
with mapcalc, but frankly, I do not know at all how to proceed. Any
help here would be greatly appreciated.

Part5 will be about secondary rivers, which will either be taken
directly from VMAP0 hydro layer or extracted with r.watershed (thank
you Markus for pointing this possibility) following the nice little
tutorial provided in the latest r.watershed manpage (bottom of the
page).
I will probably tryout both on a small scale, and keep the one
offering the best output (at my scale). The plan is to create another
vector layer showing only secondary rivers.  More on this to follow.

Part6/final: rescaling (optional), exporting and merging in GIMP.
Notice that - at least until now, very little rework is required so
that I might consider finishing the job with GRASS and export one
finished map.

Voila. I sincerely hope this progress report is of some interest,
Thank you for your time and patience when it comes to answer my
numerous questions,

regards,
Felix