Since the positional uncertainty (PU) is not available for AHD height, ‘order’ remains relevant for describing the quality of the heights.
The following table indicates the vertical accuracies of the orders and the techniques used to derive the heights quoted in the survey mark reports.
Precision | Accuracy | Order | Method |
|---|---|---|---|
12√K (mm) | +/-0.10m | 3 | 3rd order levelling |
18√K (mm) | +/-0.15m | 4 | 4th order levelling |
0.1m | +/-0.25m | 5 | GNSS (Static, Rapid Static & Kinematic) adjusted to the local levelling control network |
0.2m | +/-0.50m | 6 | GNSS (CORS RTK / RTK / PPP / AUSPOS) not adjusted to the local levelling control network |
0.5m | +/-1.00m | 7 | Doppler / Inertial / Photogrammetry / Vertical Angles / Other |
NA | NA | 9 | Scaled from topographics map |
PSM coordinates provided by industry that have a PU but no height will be assigned a height by the Office of the Surveyor-General. The height will be derived by scaling topographic maps to allow LSSA survey examination to calculate a combined scale factor and compare lodged survey plan data with PSM coordinates. These heights will be stored in the survey mark database as order 9 with the method ‘scaled’ but will not be displayed on the SAPPA or SAILIS survey mark reports. All other AHD heights (order 7 or better) will be displayed with three (3) decimal places irrespective of their derivation and accuracy.