Thursday, July 10, 2014

Chelsea Point Trig beacon

One of the local Geocacher teams, Chris'nDenise, recently placed a series of 7 caches called the Trig Beacon Series.  Six of the seven caches were placed at trig beacons along the Wild Side and Driftsands area.  The Chelsea Point Tri Beacon (I hope that's the name of the trig beacon as its the name Chris gave it in the cache description) was the third stop in the series.  Chris gave the following information about trig beacons in South Africa as the cache description.
South Africa is fully covered by the National Control Survey System which is of high accuracy and which is marked by a network of trigonometric stations and town survey marks.
The integrated survey system consists of a network of approximately 62 000 control points throughout the country. There are approximately  29 000 white beacons on mountains, hilltops and prominent man-made structures; approximately 24 000 town survey marks of brass stud in a metal box in tarred streets located in 122 cities; and approximately 20 000 benchmarks brass studs set in a concrete base originally along railway lines and alongside roads and highways.
The purpose is to provide Surveyors with a network of known co-ordinates and elevation which are critical for accurate survey for everything from roads, houses, skyscrapers to pipelines and boundaries etc.
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 responsible government department has identifies 9 836 trigonometric beacons that will be maintained. These beacons were selected using the following criteria:
  • Beacons requiring less than two hours climb
  • Block/Platform in excess of 4 meters
  • Beacons located on man made structures
  • Wind pump tower and pipe beacons
  • Tertiary beacons supplementing the above to ensure adequate horizontal control coverage around built up/development areas.
This trig beacon is on the list to be maintained.

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