[Proj] Help translating NAD83 coordinates to WGS84

[Clifford J Mugnier]

If, in fact one datum is NAD27 instead of NAD83, then there is a
substantial change to WGS84 (or to NAD83).  If you are seeing a difference
in position of over 100 feet, that is probably the problem.  The original
TIGER files were digitized from USGS Topographic maps on the NAD27.

If so, it sounds like pretty ancient data to me.

Clifford J. Mugnier
Chief of Geodesy
CENTER FOR GEOINFORMATICS
Department of Civil Engineering
LOUISIANA STATE UNIVERSITY
Baton Rouge, LA  70803
Voice and Facsimile:  (225) 578-8536 [Academic]
Voice and Facsimile:  (225) 578-4474 [Research]
================================
http://www.ASPRS.org/resources.html
http://www.ce.LSU.edu/~mugnier/
================================


Mike -

Yes, absolutely - I would certainly expect Microsoft to be using geocoding
data from a private vendor, not TIGER.  If the differences were only based
on the datum, you couldn't possibly notice them.

- 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: Michael Frumin [mailto:mfrumin at eyebeam.org]
Sent: Monday, September 20, 2004 12:13 PM
To: 'Ed McNierney';Proj at xserve.flids.com
Subject: RE: [Proj] Help translating NAD83 coordinates to WGS84

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
>
> _______________________________________________
> Proj mailing list
> Proj at xserve.flids.com
> http://xserve.flids.com/mailman/listinfo/proj
>




_______________________________________________
Proj mailing list
Proj at xserve.flids.com
http://xserve.flids.com/mailman/listinfo/proj