1. Geodetic Survey Control System of Hong Kong
Simon KWOK, SLS/G
James WONG, LS/G(NT)

2. Contents Introduction History of development
Types of Geodetic Survey Control Station
Accuracy Standards
Calibration baselines and network
Specification and Practice Guide for establishing GPS control stations
Q and A

3. Development History Horizontal Control Network
Vertical Control Network
GPS Control Network

4. Horizontal Control Network
1845
Triangulation stations first appeared on the map of Hong Kong produced by Lt. Collinson R.E.
1899/1900
Appeared on a map produced by Mr. Tate
1903/1904
Appeared on another map compiled by Mr. W.J. Newland

5. 1845, 1899/1900, 1903/1904
Although triangulation stations are shown on these maps, there is no survey record found for the triangulation.

6. Horizontal Control Network
1928/29
A military map of scale 1/20,000 was produced from air photographs taken in 1924/25 by the R.A.F. with ground controls provided by the 2nd Colonial Survey Section R.E.
These ground controls were adjusted by the Geographical Section in
1946
The above-mentioned ground control were re-adjusted by the Crown Lands and Survey Office in 1946.
It was adopted as the Main Triangulation of Hong Kong on which all surveys were based up to 1963.

7. Horizontal Control Network
1963
A re-triangulation was carried out because the network of that time could not meet the requirements of large scale mapping and cadastral surveys.
Hong Kong (1963) Geodetic Datum
Reference Ellipsoid : Clarke 1858
Datum Origin : Old Trig. “Zero”
Hong Kong (1963) Grid System
Map Projection : Cassini Projection
Projection Origin : Old Trig. No.2

8. Horizontal Control Network
Metrication policy in the 1970s
Imperial grid was converted to metric unit of measure
Grid origin was further shifted 3550 m to the west

9. Horizontal Control Network
Introduction of EDM
Re-survey the distances between hilltop stations for improving the consistence and accuracy of the control network
HK 1980 Geodetic Datum
Reference Ellipsoid : International Hayford (1910)
Hong Kong 1980 Grid System
Map projection : Transverse Mercator Projection

10. Hong Kong 1980 Geodetic Datum
Reference Ellipsoid : International Hayford (1910)
Semi-major axis (a) = m
Flattening (f) = 1 / 297
Origin : Old Trig. “Zero” at the Observatory
Latitude : 22° 18’ 12.82” N
Longitude : 114° 10’ 18.75” E
Azimuth
Trig to Trig. 94 : 292° 59’ 46.5”
Determined by astronomical Observations in 1960 by a team of visiting Geodesists who assessed the accuracy to be ±0.2”

11. Hong Kong 1980 Grid System
Reference Ellipsoid : International Hayford (1910)
Map Projection : Transverse Mercator
Projection Origin : Old Trig. 2
Latitude : 22° 18’ 43.68” N
Longitude : 114° 10’ 42.80” E
Northing : m
Easting : m
Scale Factor
Unity along central meridian at old Trig. 2

12. Vertical Control Network
1866
The surveyors of the surveying vessel “Rifleman” fixed a bench mark (Rifleman’s Bolt) for surveying the foreshore of Victoria Harbour.
The highest point of the Bolt was taken as 17 feet 10 inches above the zero level which is now known as the Hong Kong Principal datum (HKPD).
All heights and levels on land refer to this datum.

13. Vertical Control Network
Rifleman’s Bolt
Originally fixed on the wall of No.12 storehouse of Naval Dockyard in Admiralty
Upon demolition of the Dockyard, the Bolt was relocated and refixed on the wall of Blake Block in H.M.S. Tamar Naval Base in Central
Preserved for its historical value and not to be used as a bench mark
In 1997, the British Forces donated the Rifleman’s Bolt to SMO

14. Original Location of Rifleman’s Bolt

15. Rifleman’s Bolt

16. Rifleman’s Bolt

17. GPS Control Network 1991 GPS Network 2000 GPS Network
Satellite Positioning Reference Station Network

18. 1991 GPS Network First Hong Kong GPS Network
Joint Survey : Hong Kong, Macau and
British Forces (512 Specialist Team Royal Engineers (STRE))
Hong Kong Network : 15 Stations
13 existing triangulation stations
4 satellite Doppler stations
Absolute position of Doppler stations as origin
Reference frame : WGS84 (STRE 91)

19. 1991 GPS Network Purpose Problem of the 1991 GPS Network
Link the local datum HK80 to WGS84 (STRE91)
Enable GPS equipment to be used for surveying
Problem of the 1991 GPS Network
On the top of mountains
Difficult to access

20. 2000 GPS Network Densification of 1991 GPS Network on low ground
near vehicular access
reduce logistic cost

21. 2000 GPS Network 46 stations Average distance between stations : 10km
Average Observation Time of each GPS baseline : 3 hours
No. of repeated baselines ≥ 3
Relative accuracy : ± 3mm ± 1 ppm

22. 2000 GPS Network

23. Comparison of Internal Accuracy (1991 vs 2000)
1 ppm scale error in the 1991 GPS Network
Reasons:
Full constellation of NAVSTAR satellite was not available before 1994
GPS hardware and software are improving during this decade
2000 GPS Network is more accurate.

24. Reference Frame WGS 84 (STRE 91) ITRF Origin at the centre of Earth
Doppler positioning measurement technique
1 to 2 meter absolute accuracy
ITRF
More accurate realization of the reference frame
Use combination of space techniques
GPS, VLBI, SLR, DORIS
cm level absolute accuracy
Nowadays : Broadcast and precise ephemeris are based on
ITRF system.

25. Connection of 2000 GPS Network to ITRF96
2 Hong Kong Permanent GPS Reference Stations
Fanling
Kau Yi Chau
6 Global Stations of International GPS Services for Geodynamics (IGS)
Cocos Islands (Indian Ocean)
Guam (Pacific Ocean)
Lhasa (Western China)
Shanghai (Eastern China)
Tsukuba (Japan)
Yarragadee (Australia)

27. Connection of 2000 GPS Network to ITRF96
2 months continuous GPS observation data
Baseline length : 1200 km to 5000 km
Accuracy of the ITRF96 coordinates determined in this survey is better than 2 cm
Hong Kong 2000 GPS Network shall be the GPS reference datum for all GPS surveys in Hong Kong

28. Station Summary of 2000 GPS Network Station

29. Position Difference between Reference Frames

30. Satellite Positioning Reference Station Network
2001 – Phase I
6 stations were constructed and operating.
2004 – Phase II
Other 6 stations shall be established.

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

33. Types of Geodetic Survey Control Stations
Horizontal Control Stations
Vertical Control Stations
Satellite Positioning Reference Stations

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

35. Horizontal Control Stations
Type A Triangulation Monument
Type B Triangulation Monument
Picket Box (fixed in open ground)
Picket Box with concrete platform
Picket Box (fixed on rock surface)
Urban Survey Mark

36. Type A Triangulation Monument

37. Vertical Control Stations
Number of Bench Marks in Hong kong : 1500 (Approx.)

38. Vertical Control Stations
Stainless Steel Rod Bench Mark
Stainless Steel Staple
Bedrock Bench Mark

39. Stainless Steel Rod Bench Mark

40. Bedrock Bench Mark

41. Design Drawing of Bedrock Bench Mark

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

43. Siu Lang Shui (HKSL)

44. Lam Tei (HKLT)

45. Kam Tin (HKKT)

46. Equipment Box

47. Equipment Box

48. Fanling (HKFN)

49. Equipment Cabinet of HKFN

50. Stonecutters Island (HKSC)

51. Accuracy Standards

52. Calibration Baselines and Network
Steel Band Baselines
Legislative Council Building, HK
Hong Kong Science Museum, Kowloon
North District Government Offices, NT
Plover Cove EDM Calibration Baseline
GPS Equipment Calibration Network at Ap Lei Chau

53. Plover Cove EDM Calibration Baseline

54. GPS Equipment Calibration Network at Ap Lei Chau
Location : Hill-top near Lei Tung Estate, Ap Lei Chau
Consist of 4 concrete pillars
Trig. 252
Trig. 253
Trig. 254
Trig. 255

55. GPS Equipment Calibration Network at Ap Lei Chau

56. Break

57. Discussion on the Specifications and Practice Guide for Establishing GPS Control Station

58. Q & A

59. Thank you !!