Brad Douglas wrote:
IMO, OSM is a useless kludge.
There are no specs for coordinate systems, datum, etc. That means each
data collector uploads data in the system they deem useful to them,
which makes accuracy, by any stretch of the imagination, impossible.
OSM is all WGS-84 lat/lon, or at least it is supposed to be. This is
mentioned here and there in the OSM wiki, but I guess it could be
displayed more prominently. All location information in the map database
is stored as 2d-points (WGS-84 coordinate pairs). Points can be
connected to other points to form polylines and polygons, but this
compound data is basically "projectionless" in the database. The
assumption here is that the connected points are normally close enough
together for there to be very little projection error in practice, at
least away from the poles. Certainly the projection errors are in
average smaller than the errors in the point data, most of which is
collected using GPS tracklogs and/or aerial/satellite photographs.
Anyway OSM is not meant to be the final solution in mapping. First and
foremost it's supposed to be a street/guide map, good enough to use for
road/street navigation with or without a satellite navigation receiver.
Over time it can become a useful general map as well, but it probably
will never be a good topographic or accurately surveyed map. At least it
is something that everyone can use under a CC compatible license. There
aren't that many free (as in speech) street level maps to choose from
in/of Europe. In many parts of Africa you are lucky if you can find
street level maps at all.
Tapio
PS. About OSM map use in Xastir, I can't see why you couldn't do that.
Probably best would be to convert from OSM's own format to shapefiles
and make them look pretty with dbfawk. There's a very basic utility
called osm2shp to do some basic shapefile conversions. Of course the
usefulness of OSM maps depends heavily on how fully mapped those areas
you are interested in are.
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