[OSM-dev] Fwd: [OSM-newbies] Reverse geo coding

[Michael Handerek]

Ok, I realized it that there are no guaranty of the completeness of
boundaries. Anyway, it is possible to build area geometries of
administratives in order to check if nodes belongs to or not.
Both methods have weaknesses, so in my opinion a combination of both is
the best way to get nearly proper results.
But how about the performance aspect? 

I think to organize area geometries like this. The geometries should be
generated during the import of osm data. Additionally the geometries
should be grouped by continent, country and city in order to do a top to
bottom check. So, basically the search will be done in 3 steps.
Considering that administrative boundaries are not complete and doing
the search in combination with nearest continent/country/city-nodes, may
it will be faster use bounding boxes instead of more precisely bounding
areas.

Cheers, Mic

On Thu, 2009-05-28 at 14:08 +0100, Emilie Laffray wrote:
> I have looked at the script boundaries.pl, but if you want to do a
> proper reverse geocoding the information in OSM is currently not
> enough.
> The script is very useful about generating a polygon but you can only
> do so if you have the proper data in the first place. For example,
> France doesn't have all polygons for administrative boundaries of town
> or even build up areas. Furthermore, there are instances where even
> higher level relations are not yet fully complete.
> In addition, if you look at countries like France, as opposed to UK,
> you will see that the country boundary is not consistent. The UK
> boundary has been extended probably by using ST_Buffer in the
> database, while France is using the coastline for the frontier, which
> is not consistent with UK or Belgium.
> 
> Emilie Laffray
> 
> On Thu, May 28, 2009 at 1:59 PM,  <gary at gary68.de> wrote:
> > For place polygons look in the wiki.: boundaries.pl
> >
> > -- Urspr. Mitt. --
> > Betreff: [OSM-dev] Fwd: [OSM-newbies] Reverse geo coding
> > Von: Thomas Wood <grand.edgemaster at gmail.com>
> > Datum: 28.05.2009 14:50
> >
> > Forwarding this to OSM dev from newbies.
> >
> >
> > ---------- Forwarded message ----------
> > From: Michael Handerek <osm at handerek.net>
> > Date: 2009/5/28
> > Subject: [OSM-newbies] Reverse geo coding
> > To: "newbies at openstreetmap.org" <newbies at openstreetmap.org>
> >
> >
> > Hi,
> >
> > I am new to osm. I am currently developing a prototype of a reverse geo
> > coding tool based on a local osm db. The input has to be a
> > latitude/longitude pair and the output a human readable address.
> >
> > I already handled it to extract the street name and postal code of a
> > lat/long pair using the tags of a nearest-neighbor-node. To do this with
> > a acceptable query time i use the k-nearest-neighbor algorithm
> > (http://www.bostongis.com/?content_name=postgis_nearest_neighbor_generic#130).
> >
> > Now I have to get at least the country and city name. In order to do
> > this i see two possibilities.
> >
> > 1. Searching for the nearest city node, in order to extract the
> > information from his tags.
> >
> > 2. Creating geometries for each continent, country and city in order to
> > check if nodes are within.
> >
> > May someone know some better method to get the needed information, feel
> > free to discuss.
> >
> >
> > The 1. possibility, also used by 'Where are they'
> > (http://wiki.openstreetmap.org/wiki/Where_Are_They), for me, seems to be
> > imprecise.
> >
> >
> > Regards,
> > Mic
> >
> > _______________________________________________
> > newbies mailing list
> > newbies at openstreetmap.org
> > http://lists.openstreetmap.org/listinfo/newbies
> >
> >
> >
> >
> > --
> > Regards,
> > Thomas Wood
> > (Edgemaster)
> >
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