LSD PQSL Series 2015
Geodetic Survey
Prepared by Mr KWOK King-hung
22 May 2015
1
Geodesy
Source from Wiki May 2015
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.
2
Overview
1.
2.
3.
4.
5.
Hong Kong Geodetic Datum
Map Projection and Grid System
Hong Kong Horizontal Control Network
Hong Kong SatRef
New Development of GNSS
3
Geodetic Datum
Source from Wiki May 2015
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
4
Geodetic Datum
Source from Wiki May 2015
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
5
Geodetic Datum
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
6
Hong Kong Geodetic Datum
1.
Local Datum- Hong Kong 1980 Geodetic Datum (HK80)
2.
Global Datum – the Word Geodetic System (WGS84)
7
Hong Kong Geodetic Datum
8
Hong Kong Geodetic Datum
9
Hong Kong Geodetic Datum
Au Tau
Tai Mo Shan
10
Geoid 大地水準面
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
Source: From Wiki May 2015
11
Geoid 大地水準面
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
12
Source: From ESA Science Photo Library
Geoid 大地水準面
GOCE satellite in orbit launched in 2009
Play video
13
Source: From ESA Science Photo Library
Hong Kong Height Datum
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
14
Hong Kong Height Datum
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
15
Hong Kong Height Datum
16
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.
17
Hong Kong Local Geoid
• Geoid Height
• Geoid-ellipsoid separation
• Varied with gradient
18
Hong Kong Local Geoid
Geoid Height = 282.43m – 279.604m = 2.826m
19
HKGEOID-2000
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.
20
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
21
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
22
Vertical Control Network 2013
23
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.
24
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.
25
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
27
Map Projection and Grid System
28
Map Projection and Grid System
 HK 1980 Grid Coordinates
 Geographical Grid Coordinates
 UTM Grid Coordinates
29
30
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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
32
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.
33
Hong Kong Horizontal Control Network
• 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
34
Hong Kong Horizontal Control Network
• Main and Minor Triangulation / Trilateration Network
• About 240 Stations
35
Hong Kong Horizontal Control Network
• Main and Minor Control Traverse Stations
• About 3,700 Stations
• Pillars, Picket Boxes,
Urban Suvey Marks (USM)
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Hong Kong Horizontal Control Network
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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”
38
Hong Kong GPS Control Station Network
• Marine Department
– GPS Reference Station at Kau Yi Chau
– Provide DGPS Correction Services via Radio
– Support Marine Navigation
39
Hong Kong GPS Control Station Network
• 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)
40
Hong Kong GPS Control Station Network
• 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
41
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
42
Hong Kong Satellite Positioning Reference
Station System (SatRef)
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Hong Kong Satellite Positioning Reference
Station System (SatRef)
• 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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Hong Kong Satellite Positioning Reference
Station System (SatRef)

2013
– Receive GLONASS Signals
– GPS+GLONASS Data Services
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Hong Kong Satellite Positioning Reference
Station System (SatRef)

2013
– Signed the Memorandum of Understanding for
Sharing Satellite Positioning Reference Station
Data with Cartography and Cadastre Bureau of
the Macao SAR Government
46
Hong Kong Satellite Positioning Reference
Station System (SatRef)

2014
– 3 New Reference Stations
• Sha Tau Kok
• Kau Sai Chau
• Lamma Island
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Hong Kong Satellite Positioning Reference
Station System (SatRef)
48
Hong Kong Satellite Positioning Reference
Station System (SatRef)
• Future Plan
– Exploring the possibilities for set up Reference Stations at:• Shenzhen Bay
– Process Beidou Signals
– Play video
49
Source from https://www.glonassiac.ru/en/index.php
50
Source from https://www.glonassiac.ru/en/index.php
51
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.
Source from
http://www.beidou.gov.cn/xtjs.html
52
Source from Wiki May 2015
53
BeiDou
GPS Block III
GLONASS K
21,150 km
20,180 km
19,130 km
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
54
Source from Wiki May 2015
Common GNSS Data Format
• 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
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
57
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/program
s/en/GSS/GSI/svy_specifications.htm
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Specifcations & Standards
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Specifcations & Standards
61
•
Calibration Baseline & Networks
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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Thank You
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