Datum and Projection Conversion Calculator (free download) -Instructions
E-mail questions to TatukGIS , Text by Jack Yeazel
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Revision: 20 May 2002

This calculator is being supplied courtesy of TatukGIS, the maker of  a royalty-free GIS development toolkit and aerial imagery rectification software.  The program provides converting between UTM, Long/Lat, and X,Y,Z coordinates with a large selection of datums and projections.  There are MANY datums to choose from.

In the left panel of the above example, an NAD-27 datum, UTM position has been entered in Northing, Easting, Height, Datum, Projection, and Zone.  In the right panel the NAD-27 position is being converted to the WGS-84 datum.  It is interesting see that UTM northing is a significant 209 meters more than with the NAD-27 datum. The height is about 39 meters different, but this is not a geodetic (actual) difference, but the difference in the two

In this example, the NAD-27 UTM position is being converted to WGS-84 Longitude and Latitude.  In order to do this, the WGS-84 Projection must be set to Geodetic.   Also note that the ellipsoids of the datums are displayed under the datums.
Jack Yeazel

Description of Geodetic Coordinates:
Geodetic coordinates consist of geodetic latitude (f), geodetic longitude (l), and geodetic height (h) which define the position of a point on, or near, the surface of the earth with respect to a reference ellipsoid.  Their relationship to the reference ellipsoid is shown in the figure below.  The angle between the normal SP and the equatorial (X-Y) plane is called the geodetic latitude (f) of point P.  The meridian plane containing point P is defined as the half-plane containing the Z-axis and point P.  The angle between the prime meridian (X-Z) plane and the meridian containing point P is the geodetic longitude (l) of point P.  Geodetic longitude is not defined when P lies on the Z-axis.  The distance from Q to P is called the geodetic or ellipsoidal height (h).

Description of Geocentric Coordinates:
Geocentric coordinates are Cartesian coordinates (X, Y, Z) that define the position of a point with respect to the center of mass of the earth.  The origin of the coordinate system is at the center of the reference ellipsoid.
The coordinate system is a right-handed system, with the positive X axis emerging from the ellipsoid at the equator on the prime meridian, and the positive Z axis emerging from the ellipsoid at the north pole.
Tomasz Kosinski