[OSM-dev] coastline

Martijn van Oosterhout kleptog at gmail.com
Sat Aug 16 19:02:52 BST 2008

On Wed, Aug 13, 2008 at 9:34 PM, Jon Burgess <jburgess777 at googlemail.com> wrote:
> Perhaps we can do both and have it finish in a minute or two. My changes
> need some cleaning up if we want the ram caching to be optional.

Ok, I've just committed a version with many changes and a new
parameter: RESOLUTION.

/* UserParam: RESOLUTION: The simplification level. Essentially, any nodes
 * closer to each other than this many units will be simplified away. When
 * generating files for lower zooms, setting this produces simplified shapes.
 * A good rule of thumb is 40,000,000/(2^(max_zoom+8)). In other words, 1 is
 * good for upto zoom 17. Zero disables this simplification.
 * Side Effect: Non-zero causes all shapes to be loaded in memory */

The basic idea is that you could set the resolution to 500 and then it
would simplify the shapes in a way that would make it suitable for
zoom levels <=9. With a suitable reduction of divisions you should be
able to make nice low-zoom shapefiles. The side-effect that with
resolution=1 it loads all the shapes into memory indeed makes it
*very* fast. With less divisions and high simplification it just
rockets along.

I havn't switched the coastline checker over to this version yet, so
it hasn't passed the smoke test. But it should work pretty well.

(Should probably make the options switchable on the command line at some point).

Have a nice day,
Martijn van Oosterhout <kleptog at gmail.com> http://svana.org/kleptog/

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