[OSM-talk] The long tail - lowest common denominator

[Christopher Schmidt]

On Mon, Jul 10, 2006 at 01:28:53PM +0100, Nick Black wrote:
> On 7/10/06, Christopher Schmidt <crschmidt at crschmidt.net> wrote:
> >On Mon, Jul 10, 2006 at 09:17:29AM +0100, Nick Black wrote:
> >> On 7/9/06, Lars Aronsson <lars at aronsson.se> wrote:
> >> >Nick Black wrote:
> >> >
> >> >> I'm not sure that I am  following you Lars - do you mean that we could
> >> >> use automatic feature detection to detect the edges of water features?
> >> >
> >> >Yes, that's what I was philosophizing about.  But I haven't tried
> >> >it or even planned to try it.  I'm far too lazy for that.
> >>
> >> One of the most significant features of the SRTM as a global dataset
> >> is that it is self-consistent and internal errors fall within
> >> specified and documneted thresholds.  This was acheived by a lot of
> >> post-processing work.  Part of the work involved created a global
> >> water bodies mask at the same scale (1 arc-second/3 arc-sec) as the
> >> complete topographic dataset.
> >>
> >> The mask is called the SWBD.  It is supplied in ESRI shapefile format
> >> and is downloadable from the same ftp site as the SRTM data:
> >>
> >> ftp://e0srp01u.ecs.nasa.gov/srtm/version2/
> >>
> >> So thats cool - Free 3-arc-sec water body data.  Well, its only as
> >> cool as the one degree tiles that it is supplied in.  If someone could
> >> process this data to derive a complete water-bodies mask it would be
> >> invaluable to OSM and to other projects.  A derived version of the UK
> >> SWBD is already up on Chris's OSM freemap site, where is really shows
> >> up the VMAP data (shows how coarse it is).
> >
> >Oh, you didn't mention this data was so easily available -- I don't know
> >about processing it into a single shapefile (which seems like it should
> >be almost trivial), but I can absolutely set it up so that it's rendered
> >-- should this be in addition to the water layer you offered me, or
> >should I just drop that one and use the worldwide data instead?
> 
> It depends how trivial it is to render the tiles, but once you've
> downloaded them and rendered them there will be no need for the GB
> mask we have at the moment I guess

Okay. Rendering the files is as simple as pie -- just need to run them
through ogrtindex, and all is well. I'm fetching the data now, should be
done in about three hours. I just wanted to make sure you hadn't done
any additional post-processing on the UK data that would make it better
than the existing SWBD data.

-- 
Christopher Schmidt
Web Developer