Geodesy is the study of the earth and its movement over time.
Geodetic surveys are conducted with the highest degree of accuracy to provide widely spaced control points on the earth surface. Provision of the control points is based on the principle of surveying from the whole to the part and not from the part to the whole.
Geodetic surveys require the use of sophisticated instruments, accurate methods of observations and their computation with accurate adjustment.
Intergovernmental Committee on Surveying and Mapping
The Intergovernmental Committee on Surveying and Mapping (ICSM) are the national governing authority on geodesy.
Within ICSM, a committee of technical specialists from each of its jurisdictions, the ICSM Geodesy Working Group, coordinates geodetic projects across Australia and assists ICSM to meet its objectives.
Some key national initiatives include:
Geoscience Australia is the national focal point for coordination of geodetic information and data, and maintains a national network of geomagnetic observatories, forming part of a global observatory network.
Some key national projects include:
Survey Operations Unit
Our Survey Operations Unit is responsible for the development and maintenance of geodetic infrastructure and deliver services to support positioning in South Australia. It maintains the state’s survey data base which provides the positional reference for the cadastre and its graphical representation.
Key initiatives of the unit include:
- SA input to the National Positioning Infrastructure
- refine and maintain SA GDA 2020 Dataset
- provide and maintain a geodetic ground station network
- cadastral integrity through the protection and coordination of permanent survey marks
- provide the datum to underpin the foundation spatial data sets
- maintenance of an AHD height network.
Published permanent survey mark coordinates
The Survey Mark Database (SDB) is maintained by our Survey Operations Unit, and delivers the Map Grid of Australia 2020 (MGA2020) coordinates for survey marks.
Survey Mark details ordered from the South Australian Property and Planning Atlas (SAPPA) and SAILIS report MGA2020 coordinates and other details of permanent survey marks (PSMs). SAPPA should be used as the primary search tool for PSMs mark details as the report contains additional fields to the SAILIS survey mark report.
Map Grid of Australia 94 (MGA94) coordinates of survey marks are no longer available from SAPPA or SAILIS.
Download a static version of the SDB MGA94 PSM coordinates - updated 1 December 2018.
View Historical GDA94 versions on Data SA.
The positional uncertainty (PU) of MGA2020 coordinates is reported with the survey mark details. PU of coordinates is an indication of the accuracy of the coordinates compared to the reference datum (GDA2020) and determines which marks can be used as datum for surveys and control points to coordinate new survey marks.
PSMs in known reactive soil areas will be assigned a Type B PU attribute that may increase their PU. Type B is an international standard relating to measurement uncertainty based on environmental factors.
Voluntary provision of permanent survey mark data and coordinates
Coordinates of survey marks that are not provided as a requirement of certified survey plans can be provided to the Survey Operations Unit on a voluntary basis. This information may assist with spatial cadastre improvements and national network adjustments.
Complete the Provision of PSM coordinates form to provide the Surveyor-General with coordinates for permanent survey marks.
Information regarding Vertical Detail accuracies
As positional uncertainty (PU) cannot be used to describe the quality of an AHD height, ‘order’ remains relevant for vertical details.
The following table assists users to understand the indicative vertical accuracies of the orders and the techniques used to derive the heights quoted in the survey mark reports.
|12√K (mm)||+/- 0.1m||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||+/- 0.5m||6||GNSS (CORS RTK / RTK / PPP / AUSPOS) not adjusted to the local levelling control network|
|0.5m||+/- 1m||7||Doppler / Inertial / Photogrammetry / Vertical Angles / Other|
|NA||NA||9||Scaled from topographic map|
PSM coordinates provided by industry that have a PU but no height will be assigned a height by the OSG. 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.
Australian Vertical Working Surface
The Australian Vertical Working Surface (AVWS) is a new reference surface for heights in Australia based on the Earth’s gravity field.
As part of an ongoing improvement process, the Government of South Australia is partnering with Geoscience Australia (GA) to undertake an airborne gravity survey over Adelaide and surrounding regional areas from late 2021.
This survey will collect new gravity data which will provide height information at a greater accuracy.
Height information is used when producing elevation models crucial for construction and development activities, as well as environmental risk analysis (i.e. flooding, sea level rises and bushfire risk).
Register for updates or send enquiries to: DIT.GravityAVWS@sa.gov.au