SPP-06 Surveys Using Global Positioning System (GPS)

Version 1 - 18/07/2018

This guide is intended as general information only. If you are uncertain of your rights or interests, please seek professional legal advice. Landgate staff are not able to give legal advice or to draft your documents. Please read our Terms of Use above.

1  General

Amendments to the General Regulations (gazetted 5.9.2000) removed the technology specific provisions that prevented the use of GPS for cadastral surveys without first obtaining special approval from the Surveyor General. The Regulations are now technology independent and allow for the use of GPS technology in all cadastral surveys. Surveyors responsible for surveys are to ensure the accuracy requirements of the 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 material specifically covering control surveys by GPS.

3  Geodetic Connection

Generally, each GPS 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 practical to connect to a geodetic 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 GPS surveys in a particular area it is recommended that the Geodetic Survey section of Landgate be contacted for advice. Consideration may be given to an extension or densification of the network in that area.

4  Permanent Marking of GPS Stations

At least two GPS 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 field book.

5  Distant Reference Marks

In any situation where a GPS station is established individually and an azimuth is not otherwise obtainable on the ground (either by sight to another GPS 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 GPS 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:

  • GPS 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 book. (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 (GPS vectors) shall be recorded in the field book. (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 book:

  • 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 GPS observations shall be recorded in the field book.

6.4 Results

6.4.1 Control Networks

The GPS baseline observed values and adjustment results shall be recorded in the field book as follows (see examples 13 and 15 in Appendix 3):

  • the observed mean ground level distance and
  • 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 vertial datum’s upon which they are based;
  • a description of the adjustment method, constraints and software; and

6.4.2 Parcel Boundaries

The following dimensions and values relating to the parcel boundaries shall be recorded in the field book (see example 16 in Appendix 3):

  • Mid-azimuth of each straight line and of the long chord of curved boundaries,
  • Ground level distances,
  • Calculated spheroidal angles at corners (calculated from the end azimuths),
  • Parcel closure and area, and
  • GPS 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. PCG94).

6.4.3 Real Time Kinematic (RTK) Surveys

  • In addition to the requirements of 6.6.4.1 and 6.6.4.2 above, surveys by 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 field book 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. GDA94).
  • Heights can be expressed in terms of the ellipsoid or the geoid. Heights above the reference ellipsoid or spheroid (ellipsoidal, or spheroidal, heights) are derived directly from GPS 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, as long as the coordinates of every point have been supplied. (See examples 17 and 18 in Appendix 3.)

6.4.4 Geodetic Survey Controls

GPS baselines between State Geodetic Survey Marks such as Standard Survey Marks and Trigonometrical Stations 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. GDA94) on which the data is based.

See SPP-02 Searching Landgate Records for information on field book examinations and Validation and Examination Practices Section 2.3 for checklists.

6.4.5 Virtual Reference Station (VRS) Surveys

  • In addition to the requirements of 6.6.4.1 and 6.6.4.2 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 field book 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. GDA94).
  • Heights can be expressed in terms of the ellipsoid or the geoid. Heights above the reference ellipsoid or spheroid (ellipsoidal, or spheroidal, heights) are derived directly from GPS 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, preferably as long as 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 State Geodetic Marks visited (LANDGATE published coordinates) 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 field books containing authorised surveys utilising GPS, and do not absolve the surveyor from requirements under other relevant Regulations, Guidelines and Survey Instructions.

The surveyor is encouraged to include in the field book 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 GPS data files and 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 GPS 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.

This page was last updated on: 17 Mar 2020