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

Nick Black nickblack1 at gmail.com
Mon Jul 10 13:28:53 BST 2006


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

Nick




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