WCSIF NCSN Status & TSMs: 3 Oct 2019 1 - Western Cape · 2019. 10. 7. · WCSIF NCSN Status & TSMs:...

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 coordinate 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.



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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.



Trigonometrical Beacons: 29,437 monuments, 9,845 selected for maintenance;

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Geodesy: Base Datasets Identified


Town Survey Mark Schemes: 131 TSM Schemes, 28,964 monuments;

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Benchmarks: 20,431 monuments;

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TrigNet Global Navigation Satellite Systems (GNSS) Base-station network – Continuously Operating Reference System (CORS): 67 Stations;

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Geoid Model: SAGeoid2010.

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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).


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).


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



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


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.


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


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


http://www.trignet.co.za/ftp://ftp.trignet.co.za/

TrigNet


TrigNet - proposed base-stations

Bredasdorp Swellendam

Vredendal

Pofadder

Alldays Thabazimbi

Cradock Butterworth Colesberg Douglas

Vryburg Bloemhof Ficksburg

Pongola Paulpietersburg Vrede Carolina


TrigNet coverage (50km radius)


TrigNet coverage (100km radius)


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.


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.


Existing TSM Schemes


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.


Proposed TSM Schemes


Proposed and Current TSM Schemes


Proposed (Prioritised) TSM Schemes



Area NEW

Towns %

of total TSM Req.

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THAT’S IT FOLKS!!

THANK YOU!!


WCSIF NCSN Status & TSMs: 3 Oct 2019 1 - Western Cape · 2019. 10. 7. · WCSIF NCSN Status & TSMs:...

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