Survey Control Marks Database (SurCom)

Survey control marks provide a reference framework which enables the position of earth related information to be expressed in a common coordinate system. They provide a practical basis for position fixing for a wide range of users who deal with geographically related information.

Tasmanian survey control mark information is available from the Survey Control Marks Database (SurCom) from which you can:

Select survey control marks by name or number
Identify survey control in an area defined by grid or geographic coordinates
Download a variety of reports, including one in .csv format that contains an extract of basic coordinate information for all control marks in Tasmania with GDA94 and GDA2020 horizontal coordinates.

Horizontal Datums in SurCoM

Coordinates on the Geocentric Datum of Australia 2020 (GDA2020) have been available in SurCoM since 13 April 2018 and became the default coordinates provided in all station summaries and reports on 14 October 2020.

SurCoM includes the ability to select the horizontal datum coordinates will be reported in, noting that survey marks do not necessarily have a horizontal coordinate for every datum listed.

Horizontal Datums in SurCoM

There are records for over 16700 marks (existing or destroyed) with GDA2020 and GDA94 horizontal coordinates but only 15400 records have horizontal AGD66 coordinates. There are no marks with AGD84, ITRF2000, WGS72 or WGS84 coordinates on mainland Tasmania or the near islands.

In total, approximately 7200 survey control marks have an Australian Height Datum (Tasmania) 1983 (AHD83) elevation value but approximately 2000 of these marks have GDA2020 or GDA94 horizontal coordinates that have only been SCALED from a map.

GDA2020 and GDA94 ellipsoidal heights for approximately 3400 marks are available upon request from DPIPWE.

Coordinate Quality Indicators

The current Standard for the Australian Survey Control Network produced by ICSM completes the transition from CLASS and ORDER to UNCERTAINTY as the basis for evaluating and expressing the quality of measurements and survey mark coordinates that was introduced in earlier versions of the Standard. The quality of mark coordinates in SurCom for all datums other than GDA2020 is still indicated by CLASS and ORDER (as described in the SurCom Instructions page).

Positional Uncertainty or the uncertainty of the coordinates of a survey control mark with respect to datum, expressed in metres in terms of the 95% confidence level of the horizontal circular confidence region, is the only measure used to indicate the quality of horizontal GDA2020 coordinates.

Where the mark is included in the national GDA2020 least squares adjustment these values have been calculated rigorously in accordance with the formula in the Guideline for the Adjustment and Evaluation of Survey Control. If the mark isn't in the national GDA2020 adjustment the Positional Uncertainty is estimated.

GDA2020 Station Summary

In the instance of survey marks with GDA94 coordinates that were derived from an historic field survey and transformed to GDA2020 applying the NTv2 format Conformal and Distortion transformation grid the estimate is based upon empirical evaluation of the quality of a range of sample marks. GDA94 coordinates SCALED from a map are generally assigned an estimated Positional Uncertainty of 30 metres or greater. These coordinates were left unaltered since the uncertainty is so much greater than the difference between GDA94 and GDA2020 coordinates, which is around 1.5 metres in Tasmania.

The following table summarises the number of marks in nominal GDA2020 Positional Uncertainty ranges.

Horizontal Positional Uncertainty (m)	Approximate Number of Marks	Positional Uncertainty Method
0.008 – 0.025	3350	Rigorous
0.026 – 0.05	1600	Rigorous or Estimated
0.051 – 0.15	2950	Rigorous or Estimated
0.151 - 1	1400	Rigorous or Estimated
1.001 - 200	7500	Estimated

Survey Control in LISTmap

LISTMap displays the available survey control marks and you can obtain survey control station summaries with either GDA94 or GDA2020 coordinates for individual control sites. GDA94 will remain the default DISPLAY option for horizontal datum coordinates until GDA2020 is adopted to display LISTmap coordinates - see the Land Tasmania Services and Applications Datum Summary and Web Mapping and WGS84/Web-mercator pages for further details.

Go to LISTmap
The Survey Control Layer will not display at this initial zoom scale – it will display automatically when you zoom into your area of interest using any of the zooming options
Click on a survey control mark you are interested in and review the basic information in the Identify Results box or select the GDA2020 Site Summary or GDA94 Site Summary link.