[Proj] Help translating NAD83 coordinates to WGS84

[Clifford J Mugnier]

Mr. Evenden is absolutely correct in his statements.

With regard to your question about coordinate systems, there is no
practical difference between NAD83 and WGS84 unless you are concerned at
the SUB-METER level of accuracy on the ground.  For the vast majority of
GIS applications in the United States, you may consider the two datums as
synonomous.

Tiger data is generally considered good to about 40-50 feet in positional
accuracy, and was originally hand-digitized from maps referenced to the
North American Datum of 1927 (NAD27).

If you are seeing a "big" difference, it sounds like NAD27 and WGS84
datums.  In that case you need to perform a datum shift, and the most
common remedy for that in the U.S. is NADCON.

Welcome to the world of coordinate systems.  :-)

Clifford J. Mugnier
Chief of Geodesy and
Associate Director,
CENTER FOR GEOINFORMATICS
Department of Civil Engineering
CEBA 3223A
LOUISIANA STATE UNIVERSITY
Baton Rouge, LA  70803
Voice and Facsimile:  (225) 578-8536 [Academic]
Voice and Facsimile:  (225) 578-4474 [Research]
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http://www.cee.lsu.edu/facultyStaff/mugnier/index.html
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I am sorry to be a nit-picker but not "NAD 83" nor any other NAD is a
"projection."

North American Datum establishes how the geographic coordinates
are referenced and its only connection to a projection are the constants it
defines in performing a projection.  Note that projections is plural as
hundreds of
projections can be applied to geographic data of any one datum.

For the area of typical NAD application there are three projections that
are normally applied: Transverse Mercator, Lambert Conformal Conic and
Oblique Mercator.

I will now return to my cave.

On Dec 28, 2004, at 7:35 AM, Chad Wallace wrote:

Mike,



I stumbled across this site in search of projection issues. I work with a
program called MapInfo Professional, and the street files we use is in the
NAD 27 format Tiger data. Then we purchased the update which was Tiger data
using the NAD 83 projection. Once bringing the two on top of each other
there is huge differences. Is there a fix to convert our data fields? Also
what is the difference between NAD 83 & WGS 84?
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