[OSM-newbies] How to convert NAD83 to latitude/longitude?

[Gabriel Ebner]

On Sat, Dec 29, 2007 at 01:09:34PM -0700, Kelly Jones wrote:
> Thanks, Gabriel. I couldn't get ogr2ogr working (perhaps because I'm
> using dbf files?), but invproj worked great. I spot-checked the
> answers and they appear accurate. I couldn't figure out how NAD83 ==
> EPSG2258, but the results seem to bear this out.

No, NAD83 is something completely different (in kind) than EPSG 2258.

NAD83 is just a specification how to locate lat/lon coordinates in the real
world ("map datum").  It's currently for all practical purposes equal to
WGS84, which is what the coordinates from your GPS receiver are in.  There are
also other datums, e.g. in Austria there is a datum used by the national
mapping agency (EPSG 4312).  Coordinates in this datum are usually some 200
meters off compared to WGS84.

You've probably seen how maps look if you just take lat/lon coordinates and
plot them as x/y (cartesian) coordinates[1].  Note how the northern regions
(like Greenland) are stretched horizontally.  Obviously that isn't great for
taking distances, measuring angles, areas, and so on.  So over the centuries,
mappers have developed so-called projections to get maps into a more usable
state, like [2] or [3].  [2] is the projection that is used on OSM's slippy
map.  [3] is the one your raw data is in (modulo some scaling and
translation).

BTW, EPSG is just the European Petroleum Survey Group.  From the name you'd
never guess that they're publishing a cool list of geographic coordinate
systems and projected coordinate systems that is used pretty much everywhere
from GDAL over PROJ.4 to WMS.  You can search their database at [4] (try
typing 'New Mexico' in the name field).

[1] http://onearth.jpl.nasa.gov/examples/bmng.jpeg for example.
[2] http://en.wikipedia.org/wiki/Mercator_projection
[3] http://en.wikipedia.org/wiki/Transverse_Mercator_projection
[4] http://www.epsg-registry.org/

> Next question (for anyone): how do I batch upload data that's NOT a
> GPS track and isn't in GPX format? In other words, how do I upload raw XML?

XML can be many things.  E.g. GPX is also XML.

Do you mean the OSM XML format, the one you get from api.osm.org?  Probably
the easiest way to upload that is via JOSM, just open it and hit upload.

  Gabriel.