LSD PQSL Series Geodetic Survey. Prepared by Mr KWOK King-hung 22 May 2015

Transcription

1 LSD PQSL Series 2015 Geodetic Survey Prepared by Mr KWOK King-hung 22 May

2 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

3 Overview 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 3

4 Geodetic Datum Source from Wiki May 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

5 Geodetic Datum Source from Wiki May 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 the benefits of a global system outweigh the greater accuracy, the global WGS 84 datum is becoming increasingly adopted 5

6 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

7 Hong Kong Geodetic Datum 1. Local Datum- Hong Kong 1980 Geodetic Datum (HK80) 2. Global Datum the Word Geodetic System (WGS84) 7

8 Hong Kong Geodetic Datum 8

9 Hong Kong Geodetic Datum 9

10 Hong Kong Geodetic Datum Au Tau Tai Mo Shan 10

11 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

12 Geoid 大地水準面 Earth's geoid: Image produced from data obtained by the ESA's (European Space Agency) GOCE Source: From ESA Science Photo Library 12

13 Geoid 大地水準面 GOCE satellite in orbit launched in 2009 Play video Source: From ESA Science Photo Library 13

14 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 (5.435m) above zero level which is now known as HKPD Based on the MSL derived from 19 years ( ) of tidal observations taken at automatic tide guage at North Point and is 1.23m below MSL 14

15 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

16 Hong Kong Height Datum 16

17 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

18 Hong Kong Local Geoid Geoid Height Geoid-ellipsoid separation Varied with gradient 18

19 Hong Kong Local Geoid Geoid Height = m m = 2.826m 19

20 Hybrid/Combined Method - HKPU 3 steps HKGEOID-2000 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

21 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

22 Readjustment of HK Vertical Control Network Survey Results 1. A new vertical control network with higher accuracy and consistency- Vertical Control Network Permanent Bedrock Bench Marks were established 22

23 Vertical Control Network

24 Accuracy of Vertical Control Network % 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

25 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

26 8. Bedrock Bench Marks (BrBM) 26

27 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

28 Map Projection and Grid System 28

29 Map Projection and Grid System HK 1980 Grid Coordinates Geographical Grid Coordinates UTM Grid Coordinates 29

30 30

31 31

32 Part III Hong Kong Horizontal Control Network 1845 Triangulation stations first appeared on the map of Hong Kong Triangulation stations are shown on a map prepared by Mr. TATE Triangulation stations are shown on a map prepared by Mr. W.J. NEWLAND No survey record found for the triangulation 32

33 Hong Kong Horizontal Control Network 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, Ground control points readjusted by Geographical Section 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

34 Hong Kong Horizontal Control Network 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 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

35 Hong Kong Horizontal Control Network Main and Minor Triangulation / Trilateration Network About 240 Stations 35

36 Hong Kong Horizontal Control Network Main and Minor Control Traverse Stations About 3,700 Stations Pillars, Picket Boxes, Urban Suvey Marks (USM) 36

37 Hong Kong Horizontal Control Network 37

38 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

39 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

40 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

41 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

42 Hong Kong Satellite Positioning Reference Station System (SatRef) Hong Kong Satellite Positioning Reference Station Network (SatRef) Developed since 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

43 Hong Kong Satellite Positioning Reference Station System (SatRef) 43

44 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 44

45 Hong Kong Satellite Positioning Reference Station System (SatRef) 2013 Receive GLONASS Signals GPS+GLONASS Data Services 45

46 Hong Kong Satellite Positioning Reference 2013 Station System (SatRef) Signed the Memorandum of Understanding for Sharing Satellite Positioning Reference Station Data with Cartography and Cadastre Bureau of the Macao SAR Government 46

47 Hong Kong Satellite Positioning Reference Station System (SatRef) New Reference Stations Sha Tau Kok Kau Sai Chau Lamma Island 47

48 Hong Kong Satellite Positioning Reference Station System (SatRef) 48

49 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

50 Source from 50

51 Source from 51

52 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 52

53 Source from Wiki May

54 BeiDou 21,150 km GPS Block III 20,180 km GLONASS K 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 Source from Wiki May

55 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

56 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

57 Other Products and Services Geodetic Survey Services for other Government Departments Standards and Specifications Datum & Height Transformation Parameters Calibration Baselines & Network 57

58 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 58

59 Specifcations & Standards Geodetic Survey Specifications Accuracy requirements Equipment requirements Network design Field Observation procedures Computation & Error corrections Adjustment criteria Accuracy Standards of Control Survey s/en/gss/gsi/svy_specifications.htm 59

60 Specifcations & Standards 60

61 Specifcations & Standards 61

62 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 62

63 Thank You 63