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1. General
The Licensed Surveyors (General Surveying Practice) Regulations 1961 (general regulations) are technology independent and allow for the use of Global Navigation Satellite System (GNSS) technology in all cadastral surveys. Surveyors responsible for surveys are to ensure the accuracy requirements of the general regulations are met and that the field records accurately reflect the methods and results of the surveys.
2. Control Surveys
The Special Survey Area Guidelines under General Regulation 26A include information specifically covering control surveys by GNSS.
3. Geodetic Connection
Generally, each GNSS survey for cadastral purposes should be connected to the State Geodetic Network. Landgate can provide verified coordinates for geodetic survey marks that can be used as datum stations. If it is not reasonably practicable to connect to a State Geodetic Survey mark the origin of the coordinates for the datum station, and the nature of that station must be provided in the field record.
In urban areas, the two closest State Geodetic Survey Marks should be used as datum stations and to provide redundancies for the survey.
In rural areas, a State Geodetic Survey Mark within 10 km of the land the subject of the survey should be used as the datum station. If there is another State Geodetic Survey Mark within 7 km of the survey, that station should be used to provide a redundant connection.
If the State Geodetic Network is considered inadequate for efficient GNSS surveys in a particular area it is recommended that the Survey Services team of Landgate be contacted for advice. Consideration may be given to an extension or densification of the network in that area.
Connections to Continuously Operating Reference Stations (CORS) can replace the connections to conventional ground marks when such marks are outside of the 10km radius, providing that the required accuracy standards are met.
4. Permanent Marking of GNSS Stations
At least two GNSS stations within each small subdivision (more on larger rural subdivisions) should be permanently marked or referenced (horizontally, to cadastral standards of visibility and stability).
If, to get satellite visibility, stations outside the subdivision need to be occupied each should be in a secure place and be permanently marked or referenced as above.
In all cases, the relationships between these reference stations and the cadastre and the geodetic control used should be recorded in the lodged field record.
5. Distant Reference Marks
In any situation where a GNSS station is established individually, and an azimuth is not otherwise obtainable on the ground (either by sight to another GNSS station or from other lines of the survey), then a distant reference mark should also be established. The reference mark should be visible from that GNSS station and ideally at least 150 metres away from it.
6. Field Notes
6.1. Equipment
The following details for each item of equipment used in the survey are required for legal traceability purposes (see example 4 in Appendix 3):
- Manufacturer
- model number
- serial number
- calibration details and certificate number (if applicable).
This requirement is applicable, where relevant, to the following equipment types:
- GNSS receivers,
- Theodolites,
- EDM units,
- Electronic tacheometers (‘total stations’), and
- Steel bands
6.2. Method
The methods and equipment used for making measurements for each line within the survey shall be clearly recorded in the field record. (See example 13 in Appendix 3.)
Examples of methods are as follows:
- traversing
- open radiations
- Static Baselines
- Pseudo-Kinematic Baselines
- Rapid Static Baselines
- Kinematic Baselines
- Real Time Kinematic (RTK) Baselines
- Differentially derived point positions (DGPS).
Examples of the information that is required for each of these methods include:
- single or dual frequency
- number of common satellites observed
- duration of common observations.
- A summary sketch to illustrate the relationship of the baselines (GNSS vectors) shall be recorded in the field record. (See examples 13 and 16 in Appendix 3). It is essential that an independent check be made at each new parcel corner. Suitable checks include:
- re-initialisation
- re-occupation at a later time
- observations from two reference stations.
Examples of the information that is required for each of these methods include:
- single or dual frequency
- number of common satellites observed
- duration of common observations.
- A summary sketch to illustrate the relationship of the baselines (GPS vectors) shall be recorded in the field record. (See examples 13 and 16 in Appendix 3). It is essential that an independent check be made at each new parcel corner. Suitable checks include:
- re-initialisation
- re-occupation at a later time
- observations from two reference stations.
6.3. Processing
6.3.1. Datum
The following information shall be recorded in the field record:
- The datum station for the survey.
- Starting coordinates and source.
- The spatial reference system upon which the coordinates are based.
6.3.2. Software
The title and version number of the software used for processing the GNSS observations shall be recorded in the field record.
6.4. Results
6.4.1. Control Networks
The GNSS baseline observed values and adjustment results shall be recorded in the field record as follows (see examples 13 and 15 in Appendix 3):
- the observed mean ground level distance for each line
- pseudo observed mid azimuth for each line
- the adjusted mean ground level distance and adjusted mid azimuth for each line
- the adjusted three-dimensional coordinates of all points in the survey, and the horizontal and vertical datums upon which they are based
- a description of the adjustment method, constraints and software.
6.4.2. Parcel Boundaries
The following dimensions and values relating to the parcel boundaries shall be recorded in the lodged field record (see example 16 in Appendix 3):
- Mid-azimuth of each straight line and of the long chord of curved boundaries
- Ground level distances
- Calculated ellipsoidal angles at corners (calculated from the end azimuths)
- Parcel closure and area
- GNSS derived height of each boundary mark.
Grid bearings may be shown but must be either MGA or a Transverse Mercator Project Grid recognised by Landgate (e.g. PCG2020)
6.4.3. Real Time Kinematic (RTK) Surveys
In addition to the requirements of 6.4.1 and 6.4.2 above, surveys by Real Time Kinematic (RTK) shall also include the base station input coordinates, output coordinates and height of each rover station. (See examples 17 in Appendix 3.)
Where corner and intermediate marks have been set out at predetermined positions, and the plan dimensions are pre-calculated, it is recommended that the lodged field record contains a table comparing the design coordinates with the surveyed coordinates. (See example 18 in Appendix 3.)
The coordinate system adopted for the survey (e.g., arbitrary plane system) should be defined by reference to points on a geodetic datum compatible with that of the State Geodetic Network (e.g., GDA2020).
Heights can be expressed in terms of the ellipsoid or the geoid. Heights above the reference ellipsoid (ellipsoidal heights) are derived directly from GNSS observations. Heights above the geoid (orthometric heights, generally equivalent to AHD) are calculated from ellipsoidal heights by applying the geoid-ellipsoid separation (N value). If AHD heights are chosen, then the derivation of the adopted N values used in the conversion shall be stated.
Inter-station vector information in the form of grid bearings or mid-azimuths and ground level distances is preferred for spatial integration of the survey. It is sufficient to provide this information for key points within the survey, providing the coordinates of every point have been supplied. (See examples 17 and 18 in Appendix 3.)
6.4.4. Geodetic Survey Controls
GNSS baselines between State Geodetic Survey Marks are useful to Landgate for verifying and upgrading the existing geodetic network. It is also possible that Benchmarks and key cadastral points can be added to the network if reliable inter-mark relationships are provided. The best way to provide the three components of a 3D vector for this purpose is in the form of dx, dy and dz (and the standard deviations) (see example 14 in Appendix 3). It is important to specify the geodetic datum (e.g., GDA2020) on which the data is based.
See SPP-02 Searching Landgate Records for information on field record examinations and SPP-19 Validation and Examination Practices for checklists.
6.4.5. Virtual Reference Station (VRS) Surveys
In addition to the requirements of 6.4.1 and 6.4.2 above, surveys by VRS shall also include output coordinates, number of epochs observed and height of each observed station. (See example 19 in Appendix 3.)
VRS observations of the survey control network and the State Geodetic Network should be carried out concurrently.
Where corner and intermediate marks have been set out at predetermined positions, and the plan dimensions are pre-calculated, it is recommended that the lodged field record contain a table comparing the design coordinates with the surveyed coordinates. (See example 18 in Appendix 3.)
The coordinate system adopted for the survey (e.g., arbitrary plane system) should be defined by reference to points on a geodetic datum compatible with that of the State Geodetic Network (e.g., GDA2020).
Heights can be expressed in terms of the ellipsoid or the geoid. Heights above the reference ellipsoid (ellipsoidal heights) are derived directly from GNSS observations. Heights above the geoid (orthometric heights, generally equivalent to AHD) are calculated from ellipsoidal heights by applying the geoid-ellipsoid separation (N value). If AHD heights are chosen, then the comparison with the published height of any State Geodetic Survey Mark visited shall be stated.
Inter-station vector information in the form of grid bearings or mid-azimuths and ground level distances is preferred for spatial integration of the survey. It is sufficient to provide this information for key points within the survey, providing the coordinates of every point have been supplied. (See examples 17 and 18 in Appendix 3.)
All calculations are to use the observed values from the survey in question. Connections from at least two observed stations of the survey network to the two closest observed positions of the State Geodetic Marks, in accordance with 6.3 should be shown in a schematic format. (See examples 20 in Appendix 3.). A comparison between the published coordinates of State Geodetic Marks visited and the observed coordinates are to be shown, preferably in a tabular format.
Show a comparison of any redundancies, re-observations and checks using suitable survey methods
7. References
The guidelines in this chapter are considered to describe the minimum requirements for the survey and for the presentation of lodged field records containing authorised surveys using GNSS, and do not absolve the surveyor from requirements under all other relevant Regulations, Guidelines and Survey Instructions.
The surveyor is encouraged to include in the lodged field record any information additional to that required under these guidelines to demonstrate that the above mentioned requirements have been satisfied. The surveyor is also encouraged to maintain archive copies of the raw GNSS data files, processed output files and adjustment input and output files, for at least 2 years from the date of lodgement.
The two references below specify observational and processing requirements for surveys by GNSS for legal purposes:
Survey Practice Guidelines for Subdivisions within Special Survey Areas (see LSLB website).
Standards and Practices for Control Surveys (SP1), Inter-governmental Committee on Surveying and Mapping.