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Gerald Evenden | 3 Jan 2005 18:57
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Re: Help translating NAD83 coordinates to WGS84

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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Clifford J Mugnier | 3 Jan 2005 23:47
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Re: Help translating NAD83 coordinates to WGS84


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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Michael P Finn | 4 Jan 2005 08:11
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Michael P Finn of the USGS/ Mid-Continent Mapping Center is out of the office.

I will be out of the office starting  12/31/2004 and will not return until
01/05/2005.

I will be unable to check e-mail regularly while I am out. If I can't
respond to your message while I am out, then I will when I return. If you
have anything that cannot wait, please contact my colleague, Dr. Lynn
Usery, at usery <at> usgs.gov. Thanks.     Mike

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DAVID Thayer | 5 Jan 2005 18:29
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Re: Help translating NAD83 coordinates to WGS84

>>> cewallace <at> neogas.com 2004-12-28 5:35:39 AM >>>
>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?  

To fix your data you might want to have a look at the ogr2ogr utility
from
<http://ogr.maptools.org/>. I've only used it with ESRI shapefiles for
this purpose, but the documentation indicates that it works with
Mapinfo files.

HTH

dt

Dave Thayer, Public Health Engineer 
Colorado Department of Public Health and Environment
Air Pollution Control Division / Stationary Sources Program
david.thayer <at> state.co.us,   Voice:303-692-3187,   FAX:303-782-0278
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Clifford J Mugnier | 11 Jan 2005 16:37
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Re: Help translating NAD83 coordinates to WGS84


There is NO difference between NAD83 and WGS84.

None in GIS-levels of precision!

If you have a problem, that is not it!

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]
======================================================
http://www.asprs.org/resources/GRIDS/
http://www.cee.lsu.edu/facultyStaff/mugnier/index.html
======================================================

>>> cewallace <at> neogas.com 2004-12-28 5:35:39 AM >>>
>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
(Continue reading)

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Lionel Barth | 26 Jan 2005 15:15
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differents results between cs2cs and proj

Hello,

I am a new proj user.
I do not understand why I have differents results using the following 
proj and cs2cs scripts :

The script :
"proj    +proj=lcc +lat_1=45.8989 +lat_2=47.6960 +lat_0=46.8000 
+lon_0=2.33722917 \
      +a=6378249.2 +b=6356515 +x_0=600000 +y_0=2200000 \
      4.34878E 44.35930755N"
 answers "760474.90       1930742.15"

while the script :
"cs2cs    +proj=latlong +datum=WGS84 +ellps=GRS80 \
  +to    +proj=lcc +lat_1=45.8989 +lat_2=47.6960 +lat_0=46.8000 
+lon_0=2.33722917 \
      +a=6378249.2 +b=6356515 +x_0=600000 +y_0=2200000 \
      4.34878E 44.35930755N"
answers "760465.95       1931091.70 58.36"

The differences are 9 meters and about 350 meters. Does anybody know why ?

Thank you,
L. Barth

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Frank Warmerdam | 27 Jan 2005 15:54
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Re: differents results between cs2cs and proj

On Wed, 26 Jan 2005 15:15:00 +0100, Lionel Barth
<lbarth <at> hachette-livre.fr> wrote:
> Hello,
> 
> I am a new proj user.
> I do not understand why I have differents results using the following
> proj and cs2cs scripts :
> 
> The script :
> "proj    +proj=lcc +lat_1=45.8989 +lat_2=47.6960 +lat_0=46.8000
> +lon_0=2.33722917 \
>       +a=6378249.2 +b=6356515 +x_0=600000 +y_0=2200000 \
>       4.34878E 44.35930755N"
>  answers "760474.90       1930742.15"
> 
> while the script :
> "cs2cs    +proj=latlong +datum=WGS84 +ellps=GRS80 \
>   +to    +proj=lcc +lat_1=45.8989 +lat_2=47.6960 +lat_0=46.8000
> +lon_0=2.33722917 \
>       +a=6378249.2 +b=6356515 +x_0=600000 +y_0=2200000 \
>       4.34878E 44.35930755N"
> answers "760465.95       1931091.70 58.36"
> 
> The differences are 9 meters and about 350 meters. Does anybody know why ?

Lionel, 

In the "proj" case conversion is being done between your projected
space, and geographic coordinates *on the same ellipsoid*.
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Gorling, Lothar | 27 Jan 2005 15:59
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AW: differents results between cs2cs and proj

Hello,

this is correct. In first script (proj-call) you make no datum-transformation and you take the same
ellipsoid. You make only a tarsnformation from geographic coordinates to rectangle Lambert-coordinates.
In the second script (cs2cs) you make a datum-transformation from WGS and a transformation to another ellipsoid.

L. Gorling

-----Ursprüngliche Nachricht-----
Von: proj-bounces <at> xserve.flids.com [mailto:proj-bounces <at> xserve.flids.com] Im Auftrag von Lionel Barth
Gesendet: Mittwoch, 26. Januar 2005 15:15
An: proj <at> xserve.flids.com
Betreff: [Proj] differents results between cs2cs and proj

Hello,

I am a new proj user.
I do not understand why I have differents results using the following 
proj and cs2cs scripts :

The script :
"proj    +proj=lcc +lat_1=45.8989 +lat_2=47.6960 +lat_0=46.8000 
+lon_0=2.33722917 \
      +a=6378249.2 +b=6356515 +x_0=600000 +y_0=2200000 \
      4.34878E 44.35930755N"
 answers "760474.90       1930742.15"

while the script :
"cs2cs    +proj=latlong +datum=WGS84 +ellps=GRS80 \
  +to    +proj=lcc +lat_1=45.8989 +lat_2=47.6960 +lat_0=46.8000
(Continue reading)

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