GPS COORDINATE TRANSFORMATION PARAMETERS FOR JAMAICA

Abstract

The Surveying and Mapping community now has the benefit of real-time 3-dimensional coordinates at the centimetre level, through the Global Positioning System (GPS). The reference frame, World Geodetic System of 1984 (WGS84), within which a user ascertains these coordinates is essentially geocentric. In Jamaica all coordinate data and mapping are based on a non-geocentric coordinate system known as the Jamaican Datum of 1969 (JAD69), which like many others around the world was realized by making basic assumptions about the geoid-ellipsoid separation at the origin. WGS84 coordinates are therefore not compatible with the JAD69.This paper presents the results of work carried out to define the relationship between the two coordinate systems, through three types of transformation parameters, namely Block Shifts, Molodensky and Seven Parameter Similarity. Three of the forty-two primary control stations together with a Continuously Operating Reference Station (CORS), previously tied to the island network, forms a fiducial network at which WGS84 coordinates were determined. The two coordinate data sets for the four fiducial stations were used to solve the parameters. Tests were carried out on nine points with coordinates known in both systems. The results indicate that the Block Shift and Molodensky values transforms WGS84 coordinates to JAD69, accurate to ±1-2m and the seven parameter similarity values produce JAD69 coordinates accurate to ±0.5m or better. Arguments are put forward to suggest why coordinate transformation is an interim solution and that the development of a Geocentric Datum is preferred for Jamaica.