[Proj] Help translating NAD83 coordinates to WGS84

[Ed McNierney]

Mike -

In North America, NAD83 and WGS84 coordinates are so extremely similar that no conversion is necessary or appropriate in most cases.  Unless your data is acquired with a precision of millimeters (literally) you can treat the two datums as identical.  Most applications do that.  If your coordinates come from TIGER/Line data, you are already dealing with errors several orders of magnitude larger than the datum shift.  Ignore it and treat the two as identical.

The cs2cs command line you posted below converts from NAD83 to NAD83, and therefore no change should be expected.

	- Ed

Ed McNierney
President and Chief Mapmaker
TopoZone.com / Maps a la carte, Inc.
73 Princeton Street, Suite 305
North Chelmsford, MA  01863
ed at topozone.com
(978) 251-4242 

-----Original Message-----
From: proj-bounces at xserve.flids.com [mailto:proj-bounces at xserve.flids.com] On Behalf Of Michael Frumin
Sent: Monday, September 20, 2004 11:32 AM
To: Proj at xserve.flids.com
Subject: [Proj] Help translating NAD83 coordinates to WGS84

I'm having trouble converting some US coordinates from NAD83 to WGS84.
These coords were generated by geocoding addresses with US Census TIGER/Line data but I'm trying to map them onto maps generated using
WGS84 (Microsoft Mappoint maps, which use NavTech (?) data).

As is, I've been reading
http://www.remotesensing.org/proj/gen_parms.html and tried using the cs2cs utility from proj, but to no avail - no transform is actually
applied:

cs2cs -rs -f "%.10f" +proj=latlong +datum=NAD83 +to +proj=latlong
+datum=NAD83
40.76471        -73.97813
40.7647100000   -73.9781300000 0.0000000000

there are plenty examples of using cs2cs with the +ellps parameter, but I don't know what ellipses are in use.  Any thoughts there?

Also, I've seen the documentation for the +towgs option but I think it's pretty much over my head.

Any help would be awesome - it's for a cool new feature on http://www.fundrace.org

Thanks,
Mike Frumin
mfrumin at eyebeam.org

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