hong kong horizontal control network

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LSD PQSL Series 2015

Geodetic Survey

Prepared by Mr KWOK King-hung 22 May 2015

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also known as geodetics or geodetics engineering — a branch of applied mathematics and earth sciences, is the scientific discipline that deals with the measurement and representation of the Earth, including its gravitational field, in a three-dimensional time-varying space. Geodesists also study geodynamical phenomena such as crustal motion, tides, and polar motion. For this they design global and national control networks, using space and terrestrial techniques while relying on datums and coordinate systems.

Geodesy Source from Wiki May 2015

http://en.wikipedia.org/wiki/Applied_mathematics

http://en.wikipedia.org/wiki/Earth_science

http://en.wikipedia.org/wiki/Earth

http://en.wikipedia.org/wiki/Gravitational_field

http://en.wikipedia.org/wiki/Geodynamics

http://en.wikipedia.org/wiki/Crust_(geology)

http://en.wikipedia.org/wiki/Tide

http://en.wikipedia.org/wiki/Polar_motion

http://en.wikipedia.org/wiki/Control_network

http://en.wikipedia.org/wiki/Space_techniques

http://en.wikipedia.org/wiki/Datum_(geodesy)

http://en.wikipedia.org/wiki/Coordinate_system

http://en.wikipedia.org/wiki/Coordinate_system

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1. Hong Kong Geodetic Datum 2. Map Projection and Grid System 3. Hong Kong Horizontal Control Network 4. Hong Kong SatRef 5. New Development of GNSS

Overview

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1. is a coordinate system and a set of reference points, used to locate places on the Earth 2. are used in geodesy, navigation and surveying by cartographers and satellite navigation systems to translate positions indicated on maps to their real position on Earth 3. The North Pole, South Pole and Equator may be assumed to be in different positions on different datums

Geodetic Datum Source from Wiki May 2015

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4. Different datums use different estimates for the precise shape and size of the Earth 5. the Earth is an imperfect ellipsoid, localised datums can give a more accurate representation of the area of coverage than WGS 84 6. the benefits of a global system outweigh the greater accuracy, the global WGS 84 datum is becoming increasingly adopted

Geodetic Datum Source from Wiki May 2015

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7. Irregular Earth’s physical surface / Gravitational field 8. Ellipsoids does not provide a practical / meaningful reference of the 3rd dimension (height) with respective to the physical Earth 9. A separate height reference system related to the Earth surface / gravity is required

Geodetic Datum

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1. Local Datum- Hong Kong 1980 Geodetic Datum (HK80) 2. Global Datum – the Word Geodetic System (WGS84)

Hong Kong Geodetic Datum

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Tai Mo Shan

Au Tau

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A surface of constant gravity potential (equipotential surface) Closely approximates the global mean sea

level Use as Vertical Datum (HKPD 1.23m below MSL)

Represent Shape of Earth Irregular surface

Geoid 大地水準面

Source: From Wiki May 2015

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Source: From ESA Science Photo Library

Earth's geoid: Image produced from data obtained by the ESA's (European Space Agency) GOCE http://www.guardian.co.uk/science/video/2011/mar/31/gravity-map-earth-surface-goce

http://www.guardian.co.uk/science/video/2011/mar/31/gravity-map-earth-surface-goce









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Source: From ESA Science Photo Library

GOCE satellite in orbit launched in 2009

Play video

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Hong Kong Principal Datum (HKPD) Formerly known as “Ordnance Datum” “Rifleman’s Bolt”: a copper bolt fixed in Hong Kong

Naval Dockyard in 1866 The level of the “Bolt” was determined by H.M.

Surveying Vessel “Rifleman” The highest point of the Bolt was taken as 17’10”

(5.435m) above zero level which is now known as HKPD Based on the MSL derived from 19 years (1965-1983) of

tidal observations taken at automatic tide guage at North Point and is 1.23m below MSL

Hong Kong Height Datum

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Hong Kong Chart Datum (HKCD) Formerly known as “Admiralty Datum” Approximately the level of Lowest Astronomical Tide

and is adopted as the zero point for Tide Tables since 1917

For all depths, heights above mean high water mark and submarine contours on Admiralty Charts and sounding plans

HKCD = HKPD – 0.146m HKCD is 1.38m below MSL


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Height Reference Systems Height above HKPD The height of a point above HKPD means the distance measured along the vertical above the reference surface of HKPD.

HKPD is implicitly defined by the territory-wide network of bench marks established by the Geodetic Survey Section of LandsD as the elevation of them are all surveyed with reference to HKPD.

Hong Kong Local Geoid • Geoid Height • Geoid-ellipsoid separation • Varied with gradient

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Hong Kong Local Geoid

Geoid Height = 282.43m – 279.604m = 2.826m

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Hybrid/Combined Method - HKPU 3 steps Form gravimetric model Remove systematic bias of gravimetric model

by fitting with GPS/Levelling data using least square transformation linear regression or quadratic regression

Refine the transformed gravimetric model using surface interpolation. Signal extraction – different methods such as weighted average, least square collocation etc.

HKGEOID-2000

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Modernization of Height System to support accurate real-time three-dimensional

applications using GNSS Three Stages 1) Readjustment of the Hong Kong Vertical Control

Network 2) Collection of GNSS, levelling and gravity data 3) Development of a precise reference geoid model

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Readjustment of HK Vertical Control Network

Survey Results 1. A new vertical control network with higher accuracy and consistency- Vertical Control Network 2013 2. 63 Permanent Bedrock Bench Marks were established

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Vertical Control Network 2013

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Accuracy of Vertical Control Network 2013

88% of 1092 bench marks with accuracy better than 1 mm were achieved. 98% of height difference between adjoining bench marks with accuracy better than 1 mm were achieved.

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Bedrock Bench Marks (BrBM)

In order to maintain the stability and consistency of the vertical control network, 63 Permanent Bedrock Bench Marks were established in the bedrock over the territory.

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8. Bedrock Bench Marks (BrBM)

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Map Projection and Grid System Transverse Mercator Projection a) Considered as a cylinder wrapping the Earth with its axis passes

through the plane of equator b) Conformal Projection c) Grid North aligns to the True North at projection meridian

Universal Transverse Mercator Projection a) A universal projection by rotating the cylinder around the earth with 6

degrees interval in longitude

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Map Projection and Grid System

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Map Projection and Grid System HK 1980 Grid Coordinates Geographical Grid Coordinates UTM Grid Coordinates

Part III Hong Kong Horizontal Control Network • 1845

– Triangulation stations first appeared on the map of Hong Kong

• 1899-1900 – Triangulation stations are shown on a map prepared

by Mr. TATE • 1903-1904

– Triangulation stations are shown on a map prepared by Mr. W.J. NEWLAND

• No survey record found for the triangulation

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Hong Kong Horizontal Control Network • 1928-29

– Using air photographs taken in 1924/25 by the Royal Air Force – Ground controls provided by the 2nd Colonical Survey Section

Royal Engineers – Production of military map of scale 1:20,000

• 1928-30 – Ground control points readjusted by Geographical Section

• 1946-48 – Ground control points readjusted by Crown Lands and Survey

Office (former Lands Department) – Adopted as the Main Triangulation of Hong Kong on which all

surveys were based up to 1963.

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• 1957 – 100-ft long Invar Tape – Established the 100-ft standard baseline

• 1963 – Large Scale Mapping and Boundary Survey – Systematic Aerial Survey Project – Re-triangulation for the Hong Kong 1963 Geodetic Datum and Grid

System • 1976

– Metrication policy • 1978-79

– Using EDM for Distance Measurements between Trig Stations – Improved accuracy and consistence for the Network – Established the Hong Kong 1980 Geodetic Datum and Grid System

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Hong Kong Horizontal Control Network

• Main and Minor Triangulation / Trilateration Network • About 240 Stations

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• Main and Minor Control Traverse Stations • About 3,700 Stations • Pillars, Picket Boxes,

Urban Suvey Marks (USM)

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Hong Kong GPS Control Station Network

• 1990s – SMO started to apply the GPS technique – No. 512 Specialist Team, Engineers of the U.K.

Military Survey started a Territory wide observation on a network of 15 stations in Hong Kong + 3 stations in Macau using GPS and Doppler satellite techniques

– Provided a rigid link between the local HK1980 Datum and WGS84 “STRE512”

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• Marine Department – GPS Reference Station at Kau Yi Chau – Provide DGPS Correction Services via Radio – Support Marine Navigation

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• 1999 – PolyU to compute the ITRF96(1998:121)

(i.e. as at 1st May 1998) coordinates using GAMIT software for:

• Trig. No. 75 (Kau Yi Chau) • Trig. No. 430 (Fanling)

– SMO to provide Observation Data – Link to 6 International GNSS Service

(IGS) Reference Stations • Lhasa (China) • Shanghai (China) • Tsukuba (Japan) • Guam (United States) • Yarragadee (Australia) • Cocos Island (Australia)

– Connect to the International Terrestrial Reference Frame 1996 (ITRF96)

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• Hong Kong GPS 2000 Network – Adopted ITRF96

Coordinate of Trig. No. 75 as origin

– Computed ITRF96 Coordinates of 46 existing Trig Stations

– Determined the Transformation Parameters between Hong Kong 1980 Geodetic Datum and ITRF96

• Support static baseline processing & RTK survey

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Hong Kong Satellite Positioning Reference Station System (SatRef)

• Hong Kong Satellite Positioning Reference Station Network (SatRef) – Developed since 2001 – 12 Continuous Operating Reference Stations (CORS)

• 7 x 24 observations

– 3 Integrity Monitoring Stations – Data Centre and Control Centre

• Data Process and Management • Data Services delivered via Internet • Support high accuracy positioning

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• SatRef Data Services – June 2006

• Open to Government Departments & Contractors – February 2010

• Open to Public for Free – Data Services:

• RINEX Data Services – High precision & reliability positioning (Static Post-processing)

• Network RTK Data Services – cm-level real time positioning

• DGPS Data Services – m-level real time positioning

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2013 – Receive GLONASS Signals – GPS+GLONASS Data Services

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2013 – Signed the Memorandum of Understanding for

Sharing Satellite Positioning Reference Station Data with Cartography and Cadastre Bureau of the Macao SAR Government

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2014 – 3 New Reference Stations

• Sha Tau Kok • Kau Sai Chau • Lamma Island

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• Future Plan – Exploring the possibilities for set up Reference Stations at:-

• Shenzhen Bay – Process Beidou Signals – Play video

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Source from https://www.glonass-iac.ru/en/index.php

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Source from https://www.glonass-iac.ru/en/index.php

52 Source from http://www.beidou.gov.cn/xtjs.html

On 30 March 2015,China’s first New-Generation Beidou Navigation satellite was successfully launched and sent to orbit by LM-3C rocket, which has the meaning of China’s Beidou Navigation System began to expand from regional to the world.

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Source from Wiki May 2015

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21,150 km

20,180 km

19,130 km

BeiDou

GPS Block III

GLONASS K

環球貿易廣場國際金融中心二期

中環廣場中銀大廈中環中心

Source from Wiki May 2015

• RINEX (Receiver Independent Exchange Format) – Raw GNSS static data format for data processing and archive

• NMEA (National Marine Electronics Association) – Standard related to data communication between marine electronic

devices. – Transmission of GNSS position from GNSS receiver to other devices (e.g.

GNSS receiver to PDA) – For real time positioning

• RTCM SC-104 (Radio Technical Commission for Maritime Services)

– Transmission of GNSS correction from GNSS reference station to GNSS Rover

– For DGPS/RTK surveys

Common GNSS Data Format

RTCM and RINEX data in SatRef

• SatRef System – DGPS – Single-RTK – Network-RTK All GNSS corrections from SatRef are in RTCM-3.0 data format MSM – Multiple Signal Messages

• SatRef RINEX data downloaded from LandsD website are 5 second per epoch

Other Products and Services • Geodetic Survey Services for other Government

Departments • Standards and Specifications • Datum & Height Transformation Parameters • Calibration Baselines & Network

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Geodetic Survey Services • Hong Kong Observatory

– Position of Automatic Weather Stations • Hong Kong Police Force

– Laser Gun Calibration Baselines • Civil Aviation Department

– Aircraft Crash Record Survey

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Specifcations & Standards • Geodetic Survey Specifications

– Accuracy requirements – Equipment requirements – Network design – Field Observation procedures – Computation & Error

corrections – Adjustment criteria

• Accuracy Standards of Control Survey

– http://www.geodetic.gov.hk/smo/gsi/programs/en/GSS/GSI/svy_specifications.htm

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Specifcations & Standards

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Specifcations & Standards

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• Steel Band Baseline – Hong Kong: Former LegCo Building (Temporary Closed) – Kowloon: Science Museum – NT: North District Government Office

• EDM Calibration – Plover Cove EDM Calibration Baseline – Maintained by SMO, Lands Department

• GNSS Calibration – Ap Lei Chau Calibration Network

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Calibration Baseline & Networks

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Thank You

hong kong horizontal control network

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