[Proj] Help translating NAD83 coordinates to WGS84

[Michael Frumin]

I have geocoded a number of addresses with both TIGER/Line (allegedly
NAD83) data and with the proprietary data used in MS Mappoint (allegedly
WGS84) and there are significant differences for the _same address_.
Does your statement then imply that the discrepancy must be in the
underlying survey data sets for the 2 systems, not the geodetic datum
they use?

And thus there's nothing you can really do to translate from one to the
other?

Thanks,
mike


> -----Original Message-----
> From: Ed McNierney [mailto:ed at topozone.com]
> Sent: Monday, September 20, 2004 11:54 AM
> To: Michael Frumin; Proj at xserve.flids.com
> Subject: RE: [Proj] Help translating NAD83 coordinates to WGS84
> 
> 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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