[OSM-talk] Shuttle Radar Topography Mission

[Martin Spott]

Thom Shannon wrote:

> It would be good to have backgrounds like this on map tiles when zoomed 
> out, http://photojournal.jpl.nasa.gov/jpegMod/PIA06672_modest.jpg

These things indeed look really nifty. Still let me call for a little
bit of caution. Some time ago I've been experimenting with elevation
contour lines a bit - for my Landcover-DB - by converting SRTM raster
into Shapefiles. This is easily done with 'gdal_contour'. Just to
present you some numbers:

In my example a single CGIAR ZIP file of 21 MByte expands into a
GeoTIFF of 69 MByte. When converting this into elevation contour lines
of only 10 m altitude difference - which is pretty coarse ! - then the
result is a Shapefile of 518 !!! MByte (uncompressed). Now think of
what you're going to face for example if you'd try to render the whole
CGIAR set, which is approx 15 GByte compressed, into elevation contour
lines  :-)

Shapefiles are not that bad when it comes to storing vector data
efficiently, so act consideratley when you try no create nice shadings
using contour lines ....  Dealing with the raster files directly might
be an easier solution in the long run.

Cheers,
	Martin.
-- 
 Unix _IS_ user friendly - it's just selective about who its friends are !
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