[OSRS-PROJ] PROJ4 and datums

[Gerald I. Evenden]

Since the target coordinates are based upon the Bessel ellipsiod
the original WGS84 datum coordinates will almost certainly
require a datum correction.

In any case of datum conversion of cartesian data, the data must be:

1. cartesian to geographic (inverse projection),

2. datum conversion in geographic space and finally

3. converted to cartesian (forward projection).

*Nad2nad* will take care of this entire operation but ONLY for USA data.
In your case, you will need to some procedure to take care of
step 2. Proj can take care of steps 1 and 3 provided correct
ellipsoid is given.  Note, the above steps are those carried out
in *nad2nad*.

Jerry Evenden and the low riders: Katie and Daisy-Mae
gevenden at capecod.net  http://www.capecod.net/~gevenden
-----Original Message-----
From: Markus Neteler <neteler at geog.uni-hannover.de>
To: osrs-proj at remotesensing.org <osrs-proj at remotesensing.org>
Date: Monday, April 03, 2000 11:46 AM
Subject: Re: [OSRS-PROJ] PROJ4 and datums


>On Mon, Apr 03, 2000 at 11:33:45AM -0400, Gerald I. Evenden wrote:
>> Except for the North American Datum (NAD), PROJ does
>> not support datum conversions.  PROJ is system for
>> cartographic projections only.  *nad2nad* was included
>> in the PROJ distribution as an example of how to use
>> the PROJ lib.
>> 
>> Jerry Evenden and the low riders: Katie and Daisy-Mae
>> gevenden at capecod.net  http://www.capecod.net/~gevenden
>
>Yes, I understand. But my question was more related to 
>following, more general, point:
>
>Do I need datum conversion if reprojecting a map
>from UTM/WGS84 to Transverse Mercator/Bessel?
>The German system is based on Potsdam-Datum, the
>UTM datum I don't know.
>
>As nad2nad is existing, the datum conversion seems
>to be important.
>
>Kind regards
    ...

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