On Jan 3, 2008 9:31 AM, Martin Spott <[EMAIL PROTECTED]> wrote: > "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 :-)
Yeah, that's why Artem's suggestion that his rendering tool can read compressed SRTM directly caught my attention. Cheers, Andy _______________________________________________ dev mailing list [email protected] http://lists.openstreetmap.org/cgi-bin/mailman/listinfo/dev
