[OSM-dev] Coastline shapefiles

Paul Norman penorman at mac.com
Mon Jan 30 23:39:07 GMT 2012


> From: Lennard [mailto:ldp at xs4all.nl]
> Sent: Monday, January 30, 2012 12:33 PM
> To: dev at openstreetmap.org
> Subject: Re: [OSM-dev] Coastline shapefiles
> 
> 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.

How are the shoreline_300 generated? Coastcheck doesn't have any
documentation, I had to figure out what doit did and how to compile the
programs.

> 
> > 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'.

I'm querying my pgsnapshot database - I think this accounts for most of the
differences. My server runs an AMD Phenom II 1090T x6 with 6 7200 RPM drives
in RAID10


> 
> > 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.

If anyone is interested in doing something with these files, I can set up a
cron script that will run the generation and scp it somewhere.

> 
> > 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.

Since I keep a pgsnapshot database up to date, this isn't an issue for my
setup.




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