[Gdal-dev] NAD83 vs. WGS84

[Ed McNierney]

Hank -

I'll look into this a bit, but for the location and precisions you're talking about, the NAD27->WGS84 conversion IS the NAD27->NAD83 conversion.  The difference between the two should be invisible or at best microscopic - nowhere near the delta you're seeing.  I'm inclined to agree with Frank here, and you may just be grouping tools into those that are doing the datum shift and those that are not.

	- 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: Grabowski, Hank [mailto:hgrabows at stk.com]
Sent: Friday, December 12, 2003 9:43 AM
To: gdal-dev at remotesensing.org
Subject: [Gdal-dev] NAD83 vs. WGS84


The problem as I've determined is that my "NAD27->WGS84" conversion is
really just doing a "NAD27->NAD83" conversion.  The NAD27->NAD83
conversion in ESRI identically matches the conversion I'm attempting in
OGR.  Is there something wrong with the syntax of my command for the
conversion to WGS84?  

ogr2ogr -t_srs WGS84 out.shp roads.shp

My program's internal conversion to WGS84 has the exact same difference,
so I figure once I determine how to get the conversion working in
ogr2ogr I should be able to map it over to my internal code as well.  Is
it such that NAD83 is the best I can do with OGR? If that's the case
that's fine.  I just need to make that fact known to our users.

Thanks for the help guys, you've all been very responsive.
Hank
_______________________________________________
Gdal-dev mailing list
Gdal-dev at remotesensing.org
http://remotesensing.org/mailman/listinfo/gdal-dev