Using GNSS to establish a Height Datum on a Survey Richard Stanaway QUICKCLOSE.
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Transcript of Using GNSS to establish a Height Datum on a Survey Richard Stanaway QUICKCLOSE.
![Page 1: Using GNSS to establish a Height Datum on a Survey Richard Stanaway QUICKCLOSE.](https://reader030.fdocuments.us/reader030/viewer/2022020718/5513cce655034679748b4aed/html5/thumbnails/1.jpg)
Using GNSS to establisha Height Datum on a Survey
www.quickclose.com.auRichard Stanaway QUICKCLOSE
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Overview of GNSS Heighting
Height systems and Geoid models
AHD and MSL
Measuring ellipsoid Heights
Working with height datum offsets
Victorian case-study - Murray Valley LiDar
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The Geoid
Universität Stuttgart
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Heighting Surfaces
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Differences between MSL and the geoid(Mean Dynamic Topography)
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H = h - N N = h - H
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Australian Height Datum
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GDA94 Ellipsoid Height
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Ausgeoid98
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local AHD offset (o) can computed by GNSS/GPS measurements at local PMs.
o = H(AHD) – h(GDA94) + N(Ausgeoid98)
H(AHD) = h(GDA94) - N(Ausgeoid98) + o
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Complications…..
AHD20?? – 0.1 to 0.2 m higher (sea level rise)
Regional and localised subsidence (groundwater changes)
Levelling errors and mark disturbance
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Antenna Reference Point and Phase
Centre
GNSS measurements made to phase centre (and not antenna reference point)
“trunnion axis of the GPS”
Different antennas have different phase centre
offsets!!
Good advice to use phase centre heights rather than
ARP heights if different antennas are used
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Steps to get “local” AHD using GNSS/GPS
1. Determine phase centre offsets / models2. Ensure correct geoid model is used
(Ausgeoid98 or Ausgeoid09 in Victoria)
3. Take measurements at local high order (3rd order or higher) PMs/PSMs to compute offset (o)
(The Ausgeoid surface should be parallel with AHD over a localised area)
4. Apply the offset to Ausgeoid derived elevations in order to align them with local AHD
Some later GNSS systems have a local geoid builder in their software (local AHD calibration).
Alternatively, a local geoid model can be created and loaded into a GNSS controller or software
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LiDar Ground validation - example
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Ground Validation Points
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Local AHD Control
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Control Information
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Static Data Processing - Setup
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Network and Baselines
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Network and Baselines
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Results
Baselinesolutions