[Proj] Geod: I need a little guide

Paul Selormey paul at toolscenter.org
Sun Apr 25 19:33:56 EDT 2004

Hello My Prof,
Thanks for the information. After reading the sources in the
Geotrans, I searched the internet and got a lot of information
on this.
I thought proj4 was doing a similar thing with the geod program,
and also, there is a point somewhere in the proj4 docs that if you
pass in a 3-point, there is conversion of the Z and so I thought, it
was geoid conversion being applied there.

Again, thanks for the information and the support.

Any information of the format of the binary file for the geoid-ellipsoid
height conversion in the Geotrans, "egm96.grd"?

Best regards,

----- Original Message ----- 
From: "Clifford J Mugnier" <cjmce at lsu.edu>
To: <proj at remotesensing.org>
Sent: Monday, April 26, 2004 6:17 AM
Subject: Re: [Proj] Geod: I need a little guide

> EGM96 is "Earth Gravity Model 1996" and represents the relation between
> WGS84 ellipsoid AND the WGS84 datum with respect to the distance of the
> surface of equipotential energy (mean sea level) and the ellipsoid.  The
> equation is a 360-degree spherical harmonic, and the coefficients are
> unclassified.
> The surface of equipotential energy is called the "GEOID."
> When working with remotely-sensed data for topography, such as LIDAR (or
> GPS-controlled photogrammetry), the heights obtained are with respect to
> inertial reference system - centered at the center of mass of the Earth -
> the origin of the WGS84 datum and ellipsoid.  To obtain elevations from
> data, one must apply a Geoid model, commonly EGM96 - the most reliable
> geoid available.
> The query was with regard to utilizing a table of values (geoid separation
> from the ellipsoid) to convert ellipsoid heights to elevations.
> I don't think PROJ4 does that.
> Cliff Mugnier
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> Proj at remotesensing.org
> http://www.remotesensing.org/mailman/listinfo/proj

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