Tanks, but we has a problems, now the new projection is a ITRF,

We do not find information about that,

Please if you has any information, send us.


Alfonso Ochoa

----- Original Message -----
From: "Natalie Green" <[EMAIL PROTECTED]>
Sent: Thursday, March 21, 2002 10:25 AM
Subject: [geonet]: DNAG data projection on the DAP server

> Dear Geoneter's,
> It has been pointed out that DNAG gravity and magnetic data retrieved from
> the Geosoft DAP server does not reproject correctly when displayed on maps
> that are not in the native DNAG projection.  We will be loading a new,
> re-projected DNAG data set on the server by March 28 that gets around this
> problem.
> Following is an explanation of why this happens for the projection-aware
> there...
> The DNAG data uses a coordinate system based on a spheroid (called
> which is not a standard datum, such as NAD27.  Since most of the data in
> compilation was in some projection on NAD27, all data was first converted
> longitude, latitude on NAD27.  These NAD27 geographic coordinates were
> assumed to be located at the same latitude, longitude on the STM1987
> spherical datum.  The latitudes should have changed when converting from
> NAD27 ellipsoid to the STM1987 spheroid.  However, the DNAG group probably
> found it was convenient to use NAD27 latitudes because converting back to
> latitude, longitude yields the correct location on a NAD27 datum.  Modern
> software like Geosoft naturally changes the latitude, longitude when
> changing between datums, which results in the location problem people have
> observed.
> We are correcting this problem by loading a properly projected DNAG data
> that includes the correction for latitude, longitude shift between datums.
> Please be aware that any use of the DNAG data retrieved on the DAP server
> prior to March 28 will mislocate features by up to 20 km in the North-Sout
> direction.
> Please contact your local support representatives for more information.
> Kindest regards,
> Natalie Green
> ____________________________________________
> Natalie Green
> Technical Support
> Geosoft Latinoamérica Ltda.
> Av. Rio Branco, 156 Gr. 2615 - Centro
> Rio de Janeiro - RJ - BRASIL - 20043-900
> Tel: 55 21 2532-0140  Fax: 55 21 2532-7197
> Knowledge from data.
> Free Oasis montaj interface with public-domain Data Access Protocol (DAP)
> for accessing high-volume spatial data over the Internet available for
> download at www.geosoft.com/pinfo/free/downloadfree.html
> _______________________________________________________
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