[OSM-dev] Coastline shapefiles

Lennard ldp at xs4all.nl
Mon Jan 30 20:33:19 GMT 2012

On 30-1-2012 6:09, Paul Norman wrote:
> I have been experimenting with generating the coastline shapefiles locally
> using http://svn.openstreetmap.org/applications/utils/coastcheck/ and ended
> up with a few questions
> 1. Is this the same code that is currently used to generate the processed_p
> files?

Yes, except for the slight tweaking of some initial values. Also, two 
sets of shapefiles are generated, each with slightly different values 
for shape overlap. The first is processed_p, the second is another 
shapefile from which shoreline_300 is generated. The latter one takes 
more time to generate and then simplify.

> 2. It took my server about one hour from the start of extracting the
> coastline data to creating the shapefiles. My understanding was that this
> process took about a day. I'm using a different route to extract coastline
> data than osm2coast, could this account for the difference?

A full coastline shapefile run (ie. both processed_p and shoreline_300) 
takes a few hours to generate, generally. I have no doubt that current 
hardware (cpu, ssd) can have a drastic positive influence to get it to 
your 'one hour'.

> 3. If I were to run the coastline generation daily and upload the files
> somewhere, could someone then host a slippymap showing coastline errors?

I'm sure there could be ways to get that done.

> 4. Given that it only took an hour to generate, is there any way to get more
> frequent updates to the coastline files?

Another limiting factor in this is that you would need the full planet 
file, to be able to extract the coastlines. Applying diffs to update 
that planet file adds a serious amount of time to a coastline run.


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