"Andy Allan" wrote:
> One of the things I haven't worked out yet is how to render
> planet-wide contours in an efficient manner, since the shapefiles
> mulitply either in size or number to rather large amounts (for 10m
> contours especially) as I start including europe, never mind in the
> US. I found there were more than 4GB of contours for the UK, which
> made it impossible to combine the results for each SRTM->shp
> conversion into one large shp file.
Yup, at least the 'shapelib' implementation of a Shapefile
reader/writer will likely limit you to 2 GByte filesize on 32-bit and 4
GByte on 64-bit systems.
If you really would like put everything into a common storage, then you
should consider importing the resulting Shapefiles into a PostGIS
database. If you intend to use these contours together with Mapnik
then, as I understand, you'll have such thing already at hand.
Still you will have to consider storage space 'issues', no matter if
you're going to use a PostGIS DB or simply do a somehow "spatially
organized" (TM ;-) set of Shapefiles.
As an example: A 20 MByte compressed CGIAR ZIP file turns into a
Shapefile of approx. 500 MByte when you render contour lines of only
10 m distance in elevation. This is 25x the file size. So, doing a
rough estimation, the whole 15 GByte CGIAR SRTM would deliver you,
well, at least over 350 GByte of contour lines at a still really coarse
representation.
I have no doubt that PostGIS for example will handle this for you, but
you're still going to deal with a pretty huge amount of data when doing
reads. You might run into major I/O performance trouble.
When I was doing these tests, my final conclusion was to rely on raw
SRTM data without any conversion whenever possible :-)
Cheers,
Martin.
--
Unix _IS_ user friendly - it's just selective about who its friends are !
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