Trignometrical beacons, town survey marks & bench marks

The integrated survey system consists of a network of approximately 62 000 control points throughout the country. This survey system is gradually being replaced by more than 50 active GPS base stations to be known as TrigNet which provides post processing and real time GPS correction data.
The integrated survey system is 28 000 white beacons on mountains, hilltops and prominent man-made structures; 24 000 town survey marks of brass stud in a metal box in tarred streets located in 122 cities; and thousands of benchmarks brass studs set in a concrete base originally along railway lines but nowadays alongside roads and highways.

GPS has changed the manner in which geodisists and surveyors carry out their work. It has also changed the philosophy surrounding national control survey networks not only in South Africa but in many other countries around the world. The network of trigonometrical beacons on top of mountains and tall structures and buildings is known as a passive network since the beacon merely represents the position of the co-ordinate assigned to it and plays no role in updating or monitoring its position. In contrast, the current thinking lies in the establishment of active control survey networks which utilise GPS as the primary positioning tool.
The New South African Datum is referred to as the Hartebeesthoek 94 Datum and uses the World Geodetic System 1984 (WGS84) as ellipsoid of reference. The datum was implemented nationally on 1 January 1999. The benefit is that surveys and geo-spatial data all have a common datum, which facilitates the exchange of data, contributes to uniform standards of accuracy and reduces the costs of survey and spatial data to the public.
The Hartebeesthoek94 Datum enables South Africa to retain its status of possessing one of the most up to date and advanced integrated survey reference systems in the world, which affords its users the freedom to integrate their geo-spatial data in the world arena. The new datum provides South Africa with the opportunity to assist its southern African neighbours with technical and technological expertise in upgrading their geodetic.