Surveying instrument training courses at Allen Associates include a sound introduction to coordinate systems. A change for land and engineering surveying in South Africa lies ahead.
A change to South Africa’s national coordinate and projection system has been announced. With this comes profound consequences for measurement in general and will impact future surveying, mapping, engineering and high accuracy positioning applications.
*Please note that proposed changes are open for public comment until 30th November 2018.
Currently South Africa uses the Gauss Conform Projection, a special instance of the Transverse Mercator Projection that is limited to two-degree zones.
Although the Gauss Conform Projection is used in all cadastral surveying and other applications, it does hold shortcomings and presents operational challenges for users.
The Gauss Conform Projection preserves shape, with projection distortions increasing exponentially with distance from the central meridian. The Gauss Conform Projection is therefore restricted to two-degree zones – one degree on each side of the central meridian.
The two-degree zone is very restrictive for many applications and prevents working over coverages greater than two degrees in longitude (east-west direction).
To fully cover the extent of continental South Africa nine such zones are required.
The Chief Directorate: National Geo-spatial Information or CD:NGI is instructed by section 3A(d) of the Land Survey Act (Act 8 of 1997), to establish and maintain a national control survey system, including the definition of the South African spatial referencing system.
In an attempt to address the limitations that the Gauss Conform Projection presents for applications with large coverages, the CD:NGI has investigated alternative projection systems. Specifically, the Universal Transverse Mercator (UTM) and the Lambert Conformal Conic Projection with Two Standard Parallels having been assessed.
Internationally the UTM is used extensively and provides for six degree zones. Four zones cover South Africa, however, the projection distortions are significantly greater than the Gauss Conform Projection.
Although projection distortions may be acceptable for some applications, they would not be acceptable for applications requiring greater accuracy – such as cadastral surveys.
Because South Africa is greater in extent in the east-west direction than the north-south, a conical projection is more suited. As a result, the Lambert Conformal Conic Projection with Two Standard Parallels provides an advantage.
Two options have been considered, three zones covering four degrees in extent or four zones covering three degrees in extent.
The projection distortions are indicated in Table. 1. The four- zone option is then comparable with the projection distortions in the Gauss Conform Projection and should then be acceptable for cadastral surveys.
Table 1: Comparisons of the projections
Currently, the projected coordinate system is a left-handed coordinate system, with +y axis pointing west and +x axis pointing south, with directions measured clockwise from the south. This coordinate system is not compatible with most application software and creates problems for users.
To combat this, it’s been proposed that the system is changed to the greater accepted right-hand coordinate system – having the first x axis pointing east and the second y axis pointing north, with directions then measured clockwise from north.
Although these changes will greatly impact surveying, mapping, engineering and high accuracy positioning applications, Allen Associates surveying instrument training can help keep your business and employees ahead of the game.
We provide extensive surveying instrument training courses at affordable prices. Contact us for more information about the short courses we offer and course dates.
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