Geodetic Survey Control Geodetic Survey Control System of Hong KongSystem of Hong Kong

Simon KWOK, SLS/GSimon KWOK, SLS/GJames WONG, LS/G(NT)James WONG, LS/G(NT)

ContentsContents• IntroductionIntroduction• History of developmentHistory of development• Types of Geodetic Survey Control StationTypes of Geodetic Survey Control Station• Accuracy StandardsAccuracy Standards• Calibration baselines and networkCalibration baselines and network• Specification and Practice Guide for Specification and Practice Guide for

establishing GPS control stationsestablishing GPS control stations• Q and AQ and A

Development HistoryDevelopment History• Horizontal Control NetworkHorizontal Control Network• Vertical Control NetworkVertical Control Network• GPS Control NetworkGPS Control Network

Horizontal Control NetworkHorizontal Control Network18451845• Triangulation stations first appeared on the map Triangulation stations first appeared on the map

of Hong Kong produced by Lt. Collinson R.E.of Hong Kong produced by Lt. Collinson R.E.

1899/19001899/1900• Appeared on a map produced by Mr. TateAppeared on a map produced by Mr. Tate

1903/19041903/1904• Appeared on another map compiled by Mr. W.J. Appeared on another map compiled by Mr. W.J.

NewlandNewland

1845, 1899/1900, 1845, 1899/1900, 1903/19041903/1904 Although triangulation stations are Although triangulation stations are

shown on these maps, there is no shown on these maps, there is no survey record found for the survey record found for the triangulation.triangulation.

Horizontal Control NetworkHorizontal Control Network1928/291928/29• A military map of scale 1/20,000 was produced from air A military map of scale 1/20,000 was produced from air

photographs taken in photographs taken in 1924/251924/25 by the R.A.F. with ground by the R.A.F. with ground controls provided by the 2nd Colonial Survey Section R.E.controls provided by the 2nd Colonial Survey Section R.E.

• These ground controls were adjusted by the Geographical These ground controls were adjusted by the Geographical Section in Section in 1928-301928-30

19461946• The above-mentioned ground control were re-adjusted by The above-mentioned ground control were re-adjusted by

the Crown Lands and Survey Office in the Crown Lands and Survey Office in 19461946..• It was adopted as the Main Triangulation of Hong Kong on It was adopted as the Main Triangulation of Hong Kong on

which all surveys were based which all surveys were based up to 1963up to 1963..

Horizontal Control NetworkHorizontal Control Network19631963• A re-triangulation was carried out because the network of that tiA re-triangulation was carried out because the network of that time could not meet the requirements of large scale mapping and me could not meet the requirements of large scale mapping and cadastral surveys.cadastral surveys.• Hong Kong (1963) Geodetic DatumHong Kong (1963) Geodetic Datum

• Reference Ellipsoid : Clarke 1858Reference Ellipsoid : Clarke 1858• Datum Origin :Datum Origin : Old Trig. “Zero”Old Trig. “Zero”

• Hong Kong (1963) Grid SystemHong Kong (1963) Grid System• Map Projection : Cassini ProjectionMap Projection : Cassini Projection• Projection Origin : Old Trig. No.2Projection Origin : Old Trig. No.2

Horizontal Control NetworkHorizontal Control Network1975-771975-77• Metrication policy in the 1970sMetrication policy in the 1970s• Imperial grid was converted to metric unit of Imperial grid was converted to metric unit of

measuremeasure• Grid origin was further shifted 3550 m to the westGrid origin was further shifted 3550 m to the west

Horizontal Control NetworkHorizontal Control Network1978-19791978-1979• Introduction of EDMIntroduction of EDM• Re-survey the distances between hilltop stations for iRe-survey the distances between hilltop stations for improving the consistence and accuracy of the control mproving the consistence and accuracy of the control networknetwork• HK 1980 Geodetic DatumHK 1980 Geodetic Datum

• Reference Ellipsoid : International Hayford (1910)Reference Ellipsoid : International Hayford (1910)• Hong Kong 1980 Grid SystemHong Kong 1980 Grid System

• Map projection : Transverse Mercator ProjectionMap projection : Transverse Mercator Projection

Hong Kong 1980 Geodetic Hong Kong 1980 Geodetic DatumDatum• Reference Ellipsoid : International Hayford (1910)Reference Ellipsoid : International Hayford (1910)

• Semi-major axis (a) = 6378388 mSemi-major axis (a) = 6378388 m• Flattening (f) = 1 / 297Flattening (f) = 1 / 297

• Origin : Old Trig. “Zero” at the ObservatoryOrigin : Old Trig. “Zero” at the Observatory• Latitude : 22° 18’ 12.82” NLatitude : 22° 18’ 12.82” N• Longitude : 114° 10’ 18.75” ELongitude : 114° 10’ 18.75” E

• Azimuth Azimuth • Trig. 67.2 to Trig. 94 : 292° 59’ 46.5”Trig. 67.2 to Trig. 94 : 292° 59’ 46.5”• Determined by astronomical Observations in 1960 by a team of vDetermined by astronomical Observations in 1960 by a team of visiting Geodesists who assessed the accuracy to be ±0.2”isiting Geodesists who assessed the accuracy to be ±0.2”

Hong Kong 1980 Grid Hong Kong 1980 Grid SystemSystem• Reference Ellipsoid : International Hayford (1910)Reference Ellipsoid : International Hayford (1910)• Map Projection : Transverse MercatorMap Projection : Transverse Mercator• Projection Origin : Old Trig. 2Projection Origin : Old Trig. 2

• Latitude : 22° 18’ 43.68” NLatitude : 22° 18’ 43.68” N• Longitude : 114° 10’ 42.80” ELongitude : 114° 10’ 42.80” E• Northing : 819069.80 mNorthing : 819069.80 m• Easting : 836694.05 mEasting : 836694.05 m

• Scale FactorScale Factor• Unity along central meridian at old Trig. 2Unity along central meridian at old Trig. 2

Vertical Control NetworkVertical Control Network18661866• The surveyors of the surveying vessel “Rifleman” fixThe surveyors of the surveying vessel “Rifleman” fixed a bench mark (ed a bench mark (Rifleman’s BoltRifleman’s Bolt) for surveying the f) for surveying the foreshore of Victoria Harbour.oreshore of Victoria Harbour.• The highest point of the Bolt was taken as 17 feet 10 inThe highest point of the Bolt was taken as 17 feet 10 inches above the zero level which is now known as the ches above the zero level which is now known as the HHong Kong Principal datum (HKPD)ong Kong Principal datum (HKPD)..• All heights and levels on land refer to this datum.All heights and levels on land refer to this datum.

Vertical Control NetworkVertical Control NetworkRifleman’s BoltRifleman’s Bolt• Originally fixed on the wall of No.12 storehouse of Naval DockyarOriginally fixed on the wall of No.12 storehouse of Naval Dockyard in Admiraltyd in Admiralty• Upon demolition of the Dockyard, the Bolt was relocated and refiUpon demolition of the Dockyard, the Bolt was relocated and refixed on the wall of Blake Block in H.M.S. Tamar Naval Base in Cenxed on the wall of Blake Block in H.M.S. Tamar Naval Base in Centraltral

• Preserved for its historical value and not to be used as a bPreserved for its historical value and not to be used as a bench markench mark• In 1997, the British Forces donated the Rifleman’s Bolt to SMOIn 1997, the British Forces donated the Rifleman’s Bolt to SMO

Original Location of Rifleman’s BoltOriginal Location of Rifleman’s Bolt

Rifleman’s BoltRifleman’s Bolt

Rifleman’s BoltRifleman’s Bolt

GPS Control NetworkGPS Control Network

• 1991 GPS Network1991 GPS Network• 2000 GPS Network2000 GPS Network• Satellite Positioning Reference Station Satellite Positioning Reference Station

NetworkNetwork

1991 GPS Network1991 GPS Network• First Hong Kong GPS NetworkFirst Hong Kong GPS Network

– Joint Survey : Hong Kong, Macau and Joint Survey : Hong Kong, Macau and British Forces British Forces (512 Specialist Team Royal Engineers (STRE))(512 Specialist Team Royal Engineers (STRE))

• Hong Kong Network : 15 StationsHong Kong Network : 15 Stations– 13 existing triangulation stations13 existing triangulation stations– 4 satellite Doppler stations4 satellite Doppler stations

• Absolute position of Doppler stations as Absolute position of Doppler stations as originorigin

• Reference frame : WGS84 (STRE 91)Reference frame : WGS84 (STRE 91)

1991 GPS Network1991 GPS NetworkPurposePurpose • Link the local datum HK80 to WGS84 (STRE91)Link the local datum HK80 to WGS84 (STRE91)• Enable GPS equipment to be used for surveyinEnable GPS equipment to be used for surveyinggProblem of the 1991 GPS NetworkProblem of the 1991 GPS Network• On the top of mountainsOn the top of mountains• Difficult to accessDifficult to access

2000 GPS Network2000 GPS NetworkDensificationDensification of 1991 GPS Network of 1991 GPS Network• on low groundon low ground• near vehicular accessnear vehicular access• reduce logistic costreduce logistic cost

2000 GPS Network2000 GPS Network• 46 stations46 stations• Average distance between stations : 10kAverage distance between stations : 10kmm• Average Observation Time of each GPS bAverage Observation Time of each GPS baseline : 3 hoursaseline : 3 hours• No. of repeated baselines No. of repeated baselines ≥≥ 3 3• Relative accuracy : ± 3mm ± 1 ppmRelative accuracy : ± 3mm ± 1 ppm

2000 GPS Network2000 GPS Network

Comparison of Internal Accuracy Comparison of Internal Accuracy (1991 vs 2000)(1991 vs 2000)• 1 ppm scale error in the 1991 GPS Network1 ppm scale error in the 1991 GPS Network ReasonsReasons::

– Full constellation of NAVSTAR satellite was not avaiFull constellation of NAVSTAR satellite was not available before 1994lable before 1994– GPS hardware and software are improving during tGPS hardware and software are improving during this decadehis decade

• 2000 GPS Network is more accurate.2000 GPS Network is more accurate.

Reference FrameReference Frame• WGS 84 (STRE 91)WGS 84 (STRE 91)

– Origin at the centre of Earth Origin at the centre of Earth – Doppler positioning measurement techniqueDoppler positioning measurement technique– 1 to 2 meter absolute accuracy1 to 2 meter absolute accuracy

• ITRFITRF – More accurate realization of the reference frameMore accurate realization of the reference frame– Use combination of space techniquesUse combination of space techniques

• GPS, VLBI, SLR, DORISGPS, VLBI, SLR, DORIS• cm level absolute accuracycm level absolute accuracy

– Nowadays : Broadcast and precise ephemeris are based on Nowadays : Broadcast and precise ephemeris are based on ITRF system.ITRF system.

Connection of 2000 GPS Network to Connection of 2000 GPS Network to ITRF96ITRF96• 2 Hong Kong Permanent GPS Reference Stations2 Hong Kong Permanent GPS Reference Stations

• FanlingFanling• Kau Yi ChauKau Yi Chau

• 6 Global Stations of International GPS Services for Geo6 Global Stations of International GPS Services for Geodynamics (IGS)dynamics (IGS)• Cocos Islands (Indian Ocean)Cocos Islands (Indian Ocean)• Guam (Pacific Ocean)Guam (Pacific Ocean)• Lhasa (Western China) Lhasa (Western China) • Shanghai (Eastern China) Shanghai (Eastern China) • Tsukuba (Japan)Tsukuba (Japan)• Yarragadee (Australia)Yarragadee (Australia)

Connection of 2000 GPS Network to Connection of 2000 GPS Network to ITRF96ITRF96

• 2 months continuous GPS observation data2 months continuous GPS observation data• Baseline length : 1200 km to 5000 kmBaseline length : 1200 km to 5000 km• Accuracy of the ITRF96 coordinates Accuracy of the ITRF96 coordinates

determined in this survey is better than 2 cmdetermined in this survey is better than 2 cm• Hong Kong 2000 GPS Network shall be the Hong Kong 2000 GPS Network shall be the

GPS reference datum for all GPS surveys in GPS reference datum for all GPS surveys in Hong KongHong Kong

Station Summary of 2000 GPS Network Station Summary of 2000 GPS Network StationStation

Position Difference between Reference Position Difference between Reference FramesFrames

Satellite Positioning Reference Station NetworkSatellite Positioning Reference Station Network2001 – Phase I2001 – Phase I• 6 stations were constructed and operating.6 stations were constructed and operating.

2004 – Phase II2004 – Phase II• Other 6 stations shall be established.Other 6 stations shall be established.

Satellite Positioning Reference Station NetworkSatellite Positioning Reference Station Network• Territory-wide array of permanent GPS reference statiTerritory-wide array of permanent GPS reference stationsons• Total 12 stationsTotal 12 stations• Station Separation : 10 to 15 kmStation Separation : 10 to 15 km• In most of the Hong Kong area, users can measure basIn most of the Hong Kong area, users can measure baselines from at least 2 permanent stations which are wielines from at least 2 permanent stations which are within a distance of 10 km.thin a distance of 10 km.• Relative Accuracy : ± 3 mm ± 0.2 ppmRelative Accuracy : ± 3 mm ± 0.2 ppm

Types of Geodetic Survey Control Types of Geodetic Survey Control StationsStations

• Horizontal Control StationsHorizontal Control Stations• Vertical Control StationsVertical Control Stations• Satellite Positioning Reference StationsSatellite Positioning Reference Stations

Horizontal Control StationsHorizontal Control Stations

Number of Stations in Hong kongNumber of Stations in Hong kong• Main / Minor Triangulation Station : 230 (Approx.)Main / Minor Triangulation Station : 230 (Approx.)• Main / Minor Control Traverse Station : 3500 (Approx.)Main / Minor Control Traverse Station : 3500 (Approx.)

Horizontal Control StationsHorizontal Control Stations

• Type A Triangulation MonumentType A Triangulation Monument• Type B Triangulation MonumentType B Triangulation Monument• Picket Box (fixed in open ground)Picket Box (fixed in open ground)• Picket Box with concrete platformPicket Box with concrete platform• Picket Box (fixed on rock surface)Picket Box (fixed on rock surface)• Urban Survey MarkUrban Survey Mark

Type A Triangulation MonumentType A Triangulation Monument

Vertical Control StationsVertical Control Stations

Number of Bench Marks in Hong kong : 1500 (Approx.)Number of Bench Marks in Hong kong : 1500 (Approx.)

Vertical Control StationsVertical Control Stations

• Stainless Steel Rod Bench MarkStainless Steel Rod Bench Mark• Stainless Steel StapleStainless Steel Staple• Bedrock Bench MarkBedrock Bench Mark

Stainless Steel Rod Bench MarkStainless Steel Rod Bench Mark

Bedrock Bench MarkBedrock Bench Mark

Design Drawing of Bedrock Bench Design Drawing of Bedrock Bench MarkMark

Satellite Positioning Reference StationsSatellite Positioning Reference StationsExisting 6 StationsExisting 6 Stations• Siu Lang Shui (HKSL)Siu Lang Shui (HKSL)• Lam Tei (HKLT)Lam Tei (HKLT)• Kam Tin (HKKT)Kam Tin (HKKT)• Fanling (HKFN)Fanling (HKFN)• Shatin (HKST)Shatin (HKST)• Stonecutters Island (HKSC)Stonecutters Island (HKSC)

Siu Lang Shui (HKSL)Siu Lang Shui (HKSL)

Lam Tei (HKLT)Lam Tei (HKLT)

Kam Tin (HKKT)Kam Tin (HKKT)

Equipment BoxEquipment Box

Equipment BoxEquipment Box

Fanling (HKFN)Fanling (HKFN)

Equipment Cabinet of HKFNEquipment Cabinet of HKFN

Stonecutters Island (HKSC)Stonecutters Island (HKSC)

Accuracy StandardsAccuracy Standards

Calibration Baselines and NetworkCalibration Baselines and Network

• Steel Band BaselinesSteel Band Baselines•Legislative Council Building, HKLegislative Council Building, HK•Hong Kong Science Museum, KowloonHong Kong Science Museum, Kowloon•North District Government Offices, NTNorth District Government Offices, NT

• Plover Cove EDM Calibration BaselinePlover Cove EDM Calibration Baseline• GPS Equipment Calibration Network at Ap Lei ChaGPS Equipment Calibration Network at Ap Lei Chauu

Plover Cove EDM Calibration BaselinePlover Cove EDM Calibration Baseline

GPS Equipment Calibration Network at Ap Lei ChGPS Equipment Calibration Network at Ap Lei Chauau• Location : Hill-top near Lei Tung Estate, Ap Lei ChauLocation : Hill-top near Lei Tung Estate, Ap Lei Chau• Consist of 4 concrete pillars Consist of 4 concrete pillars

•Trig. 252Trig. 252•Trig. 253Trig. 253•Trig. 254Trig. 254•Trig. 255Trig. 255

GPS Equipment Calibration Network at Ap Lei ChGPS Equipment Calibration Network at Ap Lei Chauau

BreakBreak

Discussion on theDiscussion on theSpecifications and Practice Guide forSpecifications and Practice Guide for

Establishing GPS Control StationEstablishing GPS Control Station

Q & AQ & A

Thank you !!Thank you !!