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1 WCSIF NCSN Status & TSMs: 3 Oct 2019
RSA National Control Survey Networks
Precise Levelled network benchmarks – Land Levelling Datum (Vertical Datum);
Trigonometrical Beacon - Hartebeesthoek 94 Datum (Horizontal Datum);
Town Survey Schemes – (Horizontal and Vertical Datum extension);
TrigNet – Continuous Operating Reference System (CORS) ( ITRF);
SAGeoid2010 Model – Hybrid Geoid.
WCSIF NCSN Status & TSMs: 3 Oct 2019 2
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DATA SET DEFINITIONS
LAND SURVEY ACT (Act 8 of 1997) Definitions:
'trigonometrical station' means any survey station, including a town survey mark, erected by or under direction of the Chief Director as part of the national control survey system and for which he or she has published, or intends to publish, official co- ordinate values, and includes such other stations as may be prescribed.
WCSIF NCSN Status & TSMs: 3 Oct 2019
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‘Town Survey Mark’ means surveyed points located in defined areas, such as cities and towns, that form part of the National Control Survey System. Each has horizontal coordinates (and some have a height) that are used by surveyors for local survey projects. The mark generally consists of a brass peg embedded in the centre of a concrete block, which is placed below the tarred road surface and protected by a heavy iron cover.
‘Trigonometrical Beacon’ means surveyed points located in elevated positions, such as mountain tops and man-made structures, that form part of the National Control Survey Network. Each has a horizontal coordinate and a height. The beacon generally consists of a white concrete pillar with a detachable black vane or signal placed at its centre. They are commonly referred to as Trig Beacons.
WCSIF NCSN Status & TSMs: 3 Oct 2019
DATA SET DEFINITIONS
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‘TSM Scheme’ means a network of Town Survey Marks located in a defined area, such as a city or town, which has been officially established through publication in the Government Gazette.
‘TrigNet’ means South Africa's network of Continuously Operating Reference Stations (CORS). It streams Global Navigation Satellite Systems (GNSS) data to a Control Centre where it is processed and made available to users.
‘Benchmark' means precise levelled points located along main road transport routes, that form part of the National Control Survey System. Each has a height that are used by surveyors for local survey projects. The mark generally consists of a brass peg embedded in the centre of a concrete block.
WCSIF NCSN Status & TSMs: 3 Oct 2019
DATA SET DEFINITIONS
Trigonometrical Beacons: 29,437 monuments, 9,845 selected for maintenance;
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Geodesy: Base Datasets Identified
WCSIF NCSN Status & TSMs: 3 Oct 2019
Town Survey Mark Schemes: 131 TSM Schemes, 28,964 monuments;
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Geodesy: Base Datasets Identified
WCSIF NCSN Status & TSMs: 3 Oct 2019
Benchmarks: 20,431 monuments;
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Geodesy: Base Datasets Identified
WCSIF NCSN Status & TSMs: 3 Oct 2019
TrigNet Global Navigation Satellite Systems (GNSS) Base-station network – Continuously Operating Reference System (CORS): 67 Stations;
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Geodesy: Base Datasets Identified
WCSIF NCSN Status & TSMs: 3 Oct 2019
Geoid Model: SAGeoid2010.
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Geodesy: Base Datasets Identified
WCSIF NCSN Status & TSMs: 3 Oct 2019
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CONTRIBUTING CUSTODIANS
NGI is the Base Data Custodian, with no Contributing Custodians, for the following geospatial datasets:
Trigonometrical Beacons;
Town Survey Mark Schemes;
Benchmarks;
TrigNet Global Navigation Satellite Systems (GNSS) Base-station network (CORS);
Geoid Model – derived from gravimetric dataset (CGS).
WCSIF NCSN Status & TSMs: 3 Oct 2019
Hartebeesthoek94 Datum
Reference surface:
Name: World Geodetic System 1984 ellipsoid;
Defining parameters:
Semi-major axis (a): 6378137.0m;
Ellipsoid flattening (f): 1/298.257223563;
Angular velocity of the earth (ω): 7292115.0 x 10-11 radians/second;
Earth’s gravitational constant (GM): 3986004.418 x 108 m3/sec2.
Three-dimensional Origin and Orientation:
Name: Hartebeesthoek Radio Astronomy Telescope, Pretoria (IERS
name: 30302S001 HARTEBEESTHOEK VLBI 7232);
Position: International Terrestrial Frame 1991 (ITRF1991) epoch 1994.0
(0h00 SAST, 1 January 1994);
Orientation: Global Positioning System (GPS) Broadcast Ephemeris.
Scale: 1 (No scale factor applied).
WCSIF NCSN Status & TSMs: 3 Oct 2019 12
Reference surface: Adopted mean sea level;
Vertical Origin and Orientation:
Based on mean sea level determined from tidal observations at Cape
Town, 1900 and 1907. Verified by mean sea level determinations from
tidal observations at Durban, Port Elizabeth and East London, over
varying periods of time. These adopted mean sea levels were referred to
datum bench marks, and, subsequently, to the fundamental bench marks.
The heights, above adopted mean sea level, of the datum bench marks,
at the four principal ports. (See Table 1)
These heights were adopted for the original adjustment of the levelling
circuits, which commenced in 1943.
Note: No final adjustment of the levelling circuits has been completed till
present.
Normal to the Geoid.
Scale: 1 (No scale factor applied).
Land Levelling Datum
WCSIF NCSN Status & TSMs: 3 Oct 2019 13
Land Levelling Datum
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Land Levelling Datum
WCSIF NCSN Status & TSMs: 3 Oct 2019 15
Land Levelling Datum
Port Datum Height above
MSL (metre)
Cape Town Harbour datum (LWOST)
BM1
FBM Cape Town
- 0.678m
+ 3.589m
+ 5.432m
Durban BM Post Office
FBM Durban
+ 3.069m
+10.592m
Port Elizabeth B.M. PE1
PE1A
PE3
PE4
FBM Port Elizabeth
+ 4.278m
+ 4.292m
+10.327m
+14.232m
+72.680m
East London Neates beacon
FBM. East London
+ 5.114m
+ 3.336m Table 1: Adopted Mean Sea Level
WCSIF NCSN Status & TSMs: 3 Oct 2019 16
SAGI Technology Update Workshop: 1 September 2017
TRIG. BEACON MAINTENANCE
In July 2006 subset of 9,836 trigonometrical beacons retained within beacon
maintenance program. Criteria used:
Primary and secondary beacons requiring less than two hour’s climb;
Block/Platform beacons in excess of 4 metres;
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.
2,622 international boundary beacons and 67 TrigNet stations maintained.
Total: 12,525.
WCSIF NCSN Status & TSMs: 3 Oct 2019 17
TrigNet Stations 1999 (4 stations) Langebaan Cape Town Hermanus Pretoria 2000 (14 stations) Bethlehem Bloemfontein Calvinia De Aar Durban East London George Kimberley Ladysmith Port Elizabeth Pietermaritzburg Springbok Ulundi Mthatha 2001 (5 stations) Ellisras Middelburg Nelspruit Phalaborwa Pietersburg (Polokwane) 2002 (5 stations) Ermelo Kuruman Kroonstad Mafikeng Upington 2003 (3 stations) Aliwal North Graaff-Reinet Thohoyandou
VRS: Gauteng
VRS: KZN
VRS: W Cape
WCSIF NCSN Status & TSMs: 3 Oct 2019 18
2004 (3 stations) Beaufort West Prieksa Queenstown 2005 (3 stations) Groblersdal Nylstroom (Modimolle) Steelpoort (Mangabane) 2006 (4 stations) Grahamstown Malmesbury Stellenbosch Sutherland
2007 (3 stations) Benoni Krugersdorp Vereeniging 2008 (7 stations) Brits Bronkhorstspruit Heidelberg Ixopo Mooirivier Scottburgh Stanger
2009 (2 stations) Greytown Worcester 2010 (3 stations) Bhisho Cape Point Orkney 2011 (1 station) Potgietersrus (Mokopane) 2012 (6 stations) Kokstad Newcastle Plettenberg Bay Richards Bay Secunda Welkom 2013 (2 stations) Rustenburg Steenbras Dam
TrigNet Users:
Users register on TrigNet website (www.trignet.co.za) to access real-time
services;
Post processing data downloaded via the ftp site (ftp.trignet.co.za);
Registered users receive e-mails, letters and notifications relating to
TrigNet. Website has Status Messages relating to health of Trignet
stations. A Twitter account has been created to serve as an additional
communication mechanism (“TrigNet South Africa” → @TrigNet_RSA);
TrigNet
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http://www.trignet.co.za/ftp://ftp.trignet.co.za/
TrigNet
WCSIF NCSN Status & TSMs: 3 Oct 2019 20
TrigNet - proposed base-stations
Bredasdorp Swellendam
Vredendal
Pofadder
Alldays Thabazimbi
Cradock Butterworth Colesberg Douglas
Vryburg Bloemhof Ficksburg
Pongola Paulpietersburg Vrede Carolina
WCSIF NCSN Status & TSMs: 3 Oct 2019 21
TrigNet coverage (50km radius)
WCSIF NCSN Status & TSMs: 3 Oct 2019 22
TrigNet coverage (100km radius)
WCSIF NCSN Status & TSMs: 3 Oct 2019 23
SA Geoid Model 2010 In 2007, the Chief Directorate: National Geo-spatial Information (NGI)
commenced with the development of an accurate geoid model for South Africa,
with the aim to convert ellipsoidal heights, determined using NGI's TrigNet
GNSS Basestations, to orthometric heights on the South African Land Levelling
Datum, to an accuracy of 10 cm (design requirements).
South African geoid model 2010 (SAGM2010) relates gravimetric model to the
Land Leveling Datum.
The SAGM2010 is a hybrid model as the gravimetric model was tilted to model
the geoidal heights (diff. between ellipsoidal and orthometric heights) for the
control group of benchmarks.
The SAGM2010 consists of grid of geoidal heights spaced at 2½’ intervals
(±4.5km) across South Africa. The accuracy of the SAGM2010 is
approximately 7cm.
WCSIF NCSN Status & TSMs: 3 Oct 2019 24
SAGeoid Model 2010
The SAGeoid Model 2010 is a hybrid model as the gravimetric model was tilted to model the geoidal heights (diff. between ellipsoidal and orthometric heights) for the control group of benchmarks.
The SAGM2010 consists of grid of geoidal heights spaced at 2½’ intervals (±4.5km) across South Africa. The accuracy of the SAGM2010 is approximately 7cm.
WCSIF NCSN Status & TSMs: 3 Oct 2019 25
Existing TSM Schemes
WCSIF NCSN Status & TSMs: 3 Oct 2019 26
Existing TSM Schemes
Area EXISTING
Towns %
of total Existing
TSM
TOWN SURVEY MARK SCHEMES
LAND SURVEY ACT 8 OF 1997
42 Town survey marks
(1) If the Chief Director is satisfied that town survey marks should be officially
erected in any area or part of an area under the jurisdiction of a local
authority, to enable the positions of the corner points of all pieces of land
therein to be accurately determined, he or she may order the erection and
survey of such town survey marks as provided in this section.
(4) (a) A local authority shall within its area of jurisdiction be responsible for
the maintenance to the satisfaction of the Chief Director, of any town survey
marks erected in terms of this section, and should the local authority fail to
maintain any town survey mark the Chief Director may undertake any
necessary work at the expense of that local authority.
(b) A local authority established after the commencement of this Act shall by
the mere fact be responsible for the maintenance of the town survey marks
which were erected within its area of jurisdiction before its establishment.
WCSIF NCSN Status & TSMs: 3 Oct 2019 28
Proposed TSM Schemes
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Proposed TSM Schemes
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Proposed TSM Schemes
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Proposed and Current TSM Schemes
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Proposed (Prioritised) TSM Schemes
WCSIF NCSN Status & TSMs: 3 Oct 2019 33
Proposed TSM Schemes
Area NEW
Towns %
of total TSM Req.
35
THAT’S IT FOLKS!!
THANK YOU!!
WCSIF NCSN Status & TSMs: 3 Oct 2019