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TrigNet: The South African Network of Continuously Operating GPS Base Stations. Richard Wonnacott Chief Directorate: Surveys and Mapping Map Africa 2007 Cape Town 29-30 October 2007. Overview. General Considerations TrigNet Architecture Post Processing and Real Time Services

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Slide1 l.jpg

TrigNet:

The South African Network

of

Continuously Operating GPS

Base Stations

Richard Wonnacott

Chief Directorate: Surveys and Mapping

Map Africa 2007

Cape Town

29-30 October 2007


Slide2 l.jpg

Overview

  • General Considerations

  • TrigNet Architecture

  • Post Processing and Real Time Services

  • Methods of Delivery

  • Co-ordinate System

  • Current Status

  • Non-positioning Applications

  • Future

  • Conclusion


Slide3 l.jpg

  • Chief Directorate: Surveys & Mapping mandated to “establish and maintain a national control survey network”

  • Up until a few years ago we had a passive network of ~29000 trig beacons

  • GNSS has been around for some time

  • CDSM recognized change in philosophy and technology and has installed a network of active GNSS base stations

Introduction


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General Considerations “establish and maintain a national control survey network”

  • System must be receiver independent - RINEX, RTCM

  • System must be reliable through integrity monitoring and redundancy

  • Post processing data must be as fresh as possible

  • Cost of services must not be excessive to user

  • System must be expandable and flexible

  • System must meet the accuracy demands placed on it

  • All stations must be equipped with same basic equipment such as receivers and antennas


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Basic Design “establish and maintain a national control survey network”

  • Use SWEPOS concept

  • One control station at Mowbray

  • Redundancy built into network

  • Initially only post-processing service available

  • Have 45 stations installed and in process of expanding

  • Stations between 40 km and 300 km apart


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Reference Station Layout (1999-2006) “establish and maintain a national control survey network”

SIGNAL SPLITTER

GPS 2

GPS 1

ACCESS

SERVER 2

ACCESS

SERVER 1

HUB

PC 2

PC 1

ROUTER


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Reference Station Layout (2006-20??) “establish and maintain a national control survey network”

SIGNAL SPLITTER

GPS 2

GPS 1

HUB

ROUTER


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Examples of Stations “establish and maintain a national control survey network”


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Communications “establish and maintain a national control survey network”

Frame Relay Cloud

Diginet / VPN

Signal splitter

GPS 2

GPS 1

OR

Hub

Network Control Centre

ISDN Dial up

ISDN

Router

ROUTER

HUB

Remote station

ISDN Dialup

ISDN


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Post Processing Services “establish and maintain a national control survey network”

  • Data available in Receiver Independent Exchange format (RINEX)

    • Hourly data from 29 continuous feed stations available approximately 30 minutes after each hour of observation.

    • 24 hour data from continuous feed and daily download stations available on following day

    • Data is available via internet (ftp) , e-mail, CD etc.

    • Achievable accuracy could be 0,05 m or better depending on users receiver and antenna type, location, processing software, etc


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Real Time Service “establish and maintain a national control survey network”

  • Data available in Radio Technical Commission: Maritime format (RTCM)

  • DGPS

    • pseudo range corrections provided in RTCM V 2.3

    • sub metre accuracy possible from single base station

      • RMS 35 cm Hor and 1 m Vert irrespective of distance

    • used for navigation and GIS applications

  • RTK

    • carrier phase corrections provided in RTCM V 3.0 or V2.3

    • sub 10cm accuracy possible from single base station

      • RMS 8 cm Hor at ~100 km

    • used for precise navigation and by surveyors and

  • engineers


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Methods of Delivery “establish and maintain a national control survey network”

  • NTRIP (Network Transport of RTCM by Internet Protocol)

    • Users download RTCM (RTK and DGPS) corrections

    • from an Internet site in real time.

    • Corrections received are based either on one station or on a

    • network solution.

    • Field connection to internet can be via any technology eg GSM,

    • GPRS, Satphone etc

    • GSM & GPRS have disadvantages of coverage.

    • Low cost GPRS costs ~R2/Mb. NTRIP uses ~400 Kb/hour

    • Could be used for in-shore hydrographic work or navigation

    • Being used extensively in Europe and California


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Delivery of Services “establish and maintain a national control survey network”

Telecom Sat

OMNISTAR

Real Time Users

  • NTRIP Web Server

  • DGPS

  • RTK

GSM / GPRS

RINEX Web Server

GSM / GPRS

Land Line

etc

Active GPS Base station

Network Control Centre

Post Processing Users

Base Station / User Seperation : Post processing – Possible to get <5cm @ 500km or greater

DGPS – 35cm irrespective of distance

RTK – 8cm @ ~100 km

Base Station Centre- > user separation can be up to 400 km for DGPSand 50km for RTK


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Networked Real Time Solution 1 “establish and maintain a national control survey network”

  • Networked solution

  • User connects to control centre via internet using Network Transport of

    • RTCM via Internet Protocol (NTRIP)

  • User’s receiver sends provisional position to control centre

  • A virtual reference station is computed close to user’s provisional

    • position based on data from at least 4 actual reference stations

  • RTCM corrections then sent to user relative to the virtual station

  • Are able to provide either

    • DGPS for the whole country or;

    • RTK solution in 2 clusters - Gauteng

      - Western Cape

      - KZN planned for March 2008


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Remote Station “establish and maintain a national control survey network”

Remote Station

Remote Station

Remote Station

Network Control Centre

Networked Real Time Solution 2


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Remote Station “establish and maintain a national control survey network”

WWW

NTRIP

Remote Station

Provisional position

Provisional position

Remote Station

Remote Station

Network Control Centre

Networked Real Time Solution 3


Slide17 l.jpg

Remote Station “establish and maintain a national control survey network”

WWW

NTRIP

Remote Station

Position of virtual reference station & RTCM corrections

Position of virtual reference station & RTCM corrections

Remote Station

Remote Station

Network Control Centre

Networked Real Time Solution 4

Virtual reference station

New reference station when user 10 km from initial station


Slide18 l.jpg

  • Hartebesthoek 94 “establish and maintain a national control survey network”

  • Based on ITRF91 at epoch 1994.0 (International Terestrial Reference Frame)

  • WGS84 (reference system for GPS) very close to ITRFxx within few tens of

  • centimetres of centre of Earth

  • ITRF 2005

  • This is latest realisation of ITRF. WGS84 is even closer to ITRF2005

  • ITRF 2005 and TrigNet

  • Have changed all TrigNet co-ordinates to ITRF2005

  • Consistency within TrigNet is better using ITRF2005 co-ordinates

    • for TrigNet.

  • Users will have to transform from GPS/TrigNet based co-odrinates to

  • official Hart94 co-ordinates.

  • Hartebeesthoek 94 remains the official co-ordinate reference frame

Co-ordinate System 1


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Northings “establish and maintain a national control survey network”

Eastings

Height

Sample of TrigNet co-ordinates before and after introduction of new ITRF 2005 co-ordinates.

Port Elizabeth

Langebaan

Co-ordinate System 2


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May 2006 “establish and maintain a national control survey network”

Thohoyandau

Post process and Real time data

Ellisras

Pietersburg

Post processing data only

Phalaborwa

BOTSWANA

MOZAMBIQUE

Steelpoort

Int GNSS Service (IGS) Stations

Nylstroom

Nelspruit

Groblersdal

Proposed Post processing and

Real time data

Mafikeng

Pretoria

Krugers

Middelburg

NAMIBIA

Hartebeesthoek

Benoni

SWAZI

Kuruman

LAND

Vereeniging

Ermelo

Upington

Ulundi

Bethlehem

Bloemfontein

Ladysmith

Kimberley

Pietermaritzburg

Springbok

LESOTHO

Durban

Prieska

DeAar

AliwalNorth

Beaufort West

Umtata

Calvinia

Queenstown

Graaff-Reinet

Sutherland

Langebaanweg

Grahamstown

EastLondon

CapeTown

George

PortElizabeth

200KM

Hermanus


Slide21 l.jpg

Thohoyandau “establish and maintain a national control survey network”

Post process and Real time data

Ellisras

Pietersburg

Post processing data only

Phalaborwa

BOTSWANA

MOZAMBIQUE

Steelpoort

Int GNSS Service (IGS) Stations

Nylstroom

Nelspruit

Groblersdal

Proposed Post processing and

Real time data

Mafikeng

Pretoria

Krugers

Middelburg

NAMIBIA

Hartebeesthoek

Benoni

SWAZI

Kuruman

LAND

Vereeniging

Ermelo

Upington

Ulundi

Bethlehem

Bloemfontein

Ladysmith

Kimberley

Springbok

Pietermaritzburg

LESOTHO

Durban

Prieska

DeAar

AliwalNorth

Beaufort West

Umtata

Calvinia

Queenstown

Graaff-Reinet

Sutherland

Langebaanweg

Grahamstown

EastLondon

CapeTown

George

PortElizabeth

200KM

Hermanus

September 2007

Kroonstad

Malmesbury

Stellenbosch


Slide22 l.jpg

Applications of TrigNet data “establish and maintain a national control survey network”

  • Post processing applications

  • Surveying and GIS

  • Atmosperic science

    • Monitoring of atmospheric water vapour for climate monitoring

    • Monitoring of ionosphere for communication and positioining

  • Geophysics

    • Long term monitoring of station positions – plate techtonics

  • Real time applications

  • Surveying and GIS

  • Navigation

  • Weather forecasting & ionosphere mapping

  • Timing


Slide23 l.jpg

Non-Navigation Applications 1 “establish and maintain a national control survey network”

Plate motions

C.J.H. Hartnady, E. Calais & R. Wonnacott (2007): “ITRF2000 velocity field from the South African TrigNet GPS array and the African GNSS network: Implications for Nubia-(Rovuma-Lwandle-)Somalia plate motions” East African Rift Conference, Kampala


Slide24 l.jpg

Non-Navigation Applications 2 “establish and maintain a national control survey network”

  • Climate & Weather

    • Estimation of precipitable water vapour from network of GNSS stations in South Africa


Slide25 l.jpg

Month “establish and maintain a national control survey network”

Month

Dec

Dec

Nov

Nov

Oct

Oct

Sep

Sep

Aug

Aug

Jul

Jul

Jun

Jun

May

May

Apr

Apr

Mar

Mar

Feb

Feb

Jan

Jan

0

2

4

6

8

10

12

14

16

18

20

22

24

0

2

4

6

8

10

12

14

16

18

20

22

24

Hour of day [UT]

Hour of day [UT]

Non-Navigation Applications 3

  • Space weather

    • Ionospheric mapping of variation of annual TEC over South Africa from network of GNSS base stations

2004

2002

Thanks to B Opperman of Hermanus Magnetic Observatory for plots


Slide26 l.jpg

Future “establish and maintain a national control survey network”

  • Establish VRS cluster in KZN – Drbn, Pmbg+ 3 others by March 2008

  • Converting to VPN as means of remote and control station communication

  • by March 2008

  • Are in the process of purchasing 12 GPS/GLONASS receivers for

    • installation in WC & Gauteng by March 2008

  • Operationalize ionospheric mapping in co-operation with HMO by end 2007

  • Implications on single frequency positioning

  • Will have to consider a rebuild in about 2010 to cater for GPS

  • modernization plus GLONASS and Galileo

  • Increase co-operation with SAWS for weather forecasting and climate

  • monitoring applications


Slide27 l.jpg

Conclusion “establish and maintain a national control survey network”

  • The passive network of Trigonometrical beacons has served

  • South Africa well for nearly 100 years.

  • There is a confidence that TrigNet will serve the country just

  • as well.

  • The services available from TrigNet are easily available.

  • NTRIP is “state of the art” in real time service provisison.

  • The applications of TrigNet are not confined to positioning.

  • A rebuild is planned to accommodate GPS modernization,

    • GLONASS and Galileo.


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Thank You “establish and maintain a national control survey network”

Website for further information and data

www.trignet.co.za


Extra slides l.jpg
Extra Slides “establish and maintain a national control survey network”


Slide30 l.jpg

South African Active “establish and maintain a national control survey network”GPS Base Station Network

  • Chief Directorate: Surveys & Mapping (CDSM) mandated in terms of Land Survey Act (8 of 1997) to “establish and maintain a national control survey network”

  • Up until a few years ago we had a passive network of ~29000 trig beacons


Slide31 l.jpg

South African Active “establish and maintain a national control survey network”GPS Base Station Network

  • GPS has been around for some time

  • CDSM recognized change in philosophy and technology and has installed a network of active GPS base stations

  • Consultancy was provided by National Land

  • Survey of Sweden – strong SWEPOS influence


Slide32 l.jpg

  • Hartebesthoek 94 “establish and maintain a national control survey network”

  • Based on ITRF91 at epoch 1994.0 (International Terestrial Reference Frame)

  • WGS84 (reference system for GPS) very close to ITRFxx within few tens of

  • centimetres of centre of Earth

  • ITRF 2005

  • This is latest realisation of ITRF. WGS84 is even closer to ITRF2005

  • Testing ITRF 2005 against Hart94

  • Differences between ITRF 2005 and Hart94 co-ordinates of TrigNet stations:

  • dy = -0.139 m std dev = 0.074 m

  • dx = -0.358 m std dev = 0.059 m Lo Co-ordinates

  • dh = 0.105 m std dev = 0.167 m

  • Consistency within TrigNet will be better using ITRF2005 co-ordinates

    • for TrigNet.

  • Users will have to transform from GPS/TrigNet based co-odrinates to

  • official Hart94 co-ordinates.

Co-ordinate System


Slide33 l.jpg

Northings “establish and maintain a national control survey network”

Eastings

Height

Sample of TrigNet co-ordinates before and after introduction of new ITRF 2005 co-ordinates.

Port Elizabeth

Langebaan

Co-ordinate System


Slide34 l.jpg

Co-ordinate System “establish and maintain a national control survey network”

  • Hartebeesthoek 94 will remain the

  • official co-ordinate system


Slide35 l.jpg

Thohoyandau “establish and maintain a national control survey network”

Post process and Real time data

Ellisras

Pietersburg

Post processing data only

Phalaborwa

BOTSWANA

MOZAMBIQUE

Steelpoort

Int GNSS Service (IGS) Stations

Nylstroom

Nelspruit

Groblersdal

Proposed Post processing and

Real time data

Mafikeng

Pretoria

Krugers

Middelburg

NAMIBIA

Hartebeesthoek

Benoni

SWAZI

Kuruman

LAND

Vereeniging

Ermelo

Upington

Ulundi

Bethlehem

Bloemfontein

Ladysmith

Kimberley

Pietermaritzburg

Springbok

LESOTHO

Durban

Prieska

DeAar

AliwalNorth

Beaufort West

Umtata

Calvinia

Queenstown

Graaff-Reinet

Sutherland

Langebaanweg

Grahamstown

EastLondon

CapeTown

George

PortElizabeth

200KM

Hermanus

April 2007

Kroonstad

Malmesbury

Stellenbosch


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