[Proj] Is egm08_25.gtx misplaced half a pixel?

[Noel Zinn (cc)]

Mikael,

I can't address the registration issues with egm08_25.gtx that you raise, 
but egm08_25.gtx would have been derived from this file:

Und_min2.5x2.5_egm2008_isw=82_WGS84_TideFree

or its little endian equivalent.

I can confirm that the file I cite ranges from -90 to 90 in latitude (every 
2.5 minutes, for 4321 "rows") and 0 to 359+57.5/60 in longitude (every 2.5 
minutes, for 8640 "columns").

For what it's worth.

Noel

Noel Zinn, Principal, Hydrometronics LLC
+1-832-539-1472 (office), +1-281-221-0051 (cell)
noel.zinn at hydrometronics.com (email)
http://www.hydrometronics.com (website)

-----Original Message----- 
From: Mikael Rittri
Sent: Wednesday, October 05, 2011 8:23 AM
To: proj at lists.maptools.org
Subject: [Proj] Is egm08_25.gtx misplaced half a pixel?


Hello,

I have tried to use the geoid height file

   http://download.osgeo.org/proj/vdatum/egm08_25/egm08_25.gtx,

which is discussed here:

   http://trac.osgeo.org/proj/wiki/VerticalDatums

But I am beginning to think that the file is misaligned
(well, at least if ones uses GDAL 1.8 or later to read it).