Articles

Astronomic azimuths had been used for orienting old surveys in Ghana. With technological advancement and the development of simpler but accurate equipment and techniques for measurement, this has been replaced by the use of the Global Navigational Satellite System (GNSS) techniques such as the Global Positioning System(GPS). However, the use of these for azimuth determinations results in a different type of azimuth as opposed to astronomic azimuths previously used. For retracing some of those old surveys based on Astronomical coordinates, the relationship and convertibility between the different azimuths is imperative. In this exploration, the relationship and precision of both techniques were tested on various baselines located in different parts of the country. This involved the computation of Astronomic, Geodetic and Grid Azimuths between pairs of points to form several baselines. These baselines span from the Southern to the Middle belt portions of the Country where triangulations have been done, as some of these triangulation stations were Laplace stations that have both astronomic and geodetic coordinates determined for them. The results were investigated in terms of effect of using the convergence and t-T correction to convert between the set of azimuths. The results show that Geodetic Azimuths could be converted to grid coordinates and vice versa to accuracies of mean 0° 0ʹ 0.56ʺ and standard deviation ± 5.6 seconds. However, for Astronomic to Grid Azimuths, without correcting for Deflection of vertical, the conversion is accurate only to mean differences of 0° 1ʹ 25.3ʺ with standard deviation ± 0° 8ʹ 21.5ʺ. The results show the necessity of the Laplace correction for vertical deflection in astronomic azimuths in addition to the convergence and t-T correction and recommends the provision of country-wide deflection corrections.