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1. Scope
These guidelines are applicable to the following two situations of determining the spatial definition of easements:
- by survey and ground marking, and
- by calculation from the Spatial Cadastral Database (SCDB).
These guidelines are applicable to easements over both Crown and Freehold land.
These guidelines are particularly applicable to easements created under the Land Administration Act 1997 and the Petroleum Pipelines Act 1969 for depiction on ‘Interest Only’ plans.
The provisions in these guidelines can be adopted where authorised and applicable for the definition of other easements including those registered under the Transfer of Land Act 1893.
2. Easements by Survey and Ground Marking
2.1. General Provisions
Survey methods should conform to the basic principles of survey as defined in the Licensed Surveyors (Guidance of Surveyors) Regulations 1961 (the General Regulations).
Definition is to be achieved by surveying one side of the proposed easement, the centre line, or some other offset line. If the utility is in position at the time of survey, connections to it are required at every survey mark placed.
To facilitate verification of the easement survey and integration with the SCDB, rigorous connections to the State Geodetic Survey (geodetic connections) are required. In remote areas a surveyed connection should be made to each geodetic station within 5km of the easement route. In areas with a greater density of geodetic stations, geodetic connections should be made at intervals of not more than 5km.
The geodetic connections should be in accordance with Section 4.
2.2. Marking
Generally, easements protecting services within Crown Land in rural and pastoral areas, or access routes to those services, should be marked in accordance with the following provisions.
For other easements, ground marking is at the discretion of the surveyor and the other interested parties:
- One side of the easement should be marked.
- Angle points, surveyed intersections with existing cadastral boundaries and points at one kilometre intervals on long straights, should be marked in accordance with paragraph (a) of the Table to General Regulation 36.
- Intersections with unsurveyed boundaries do not generally need to be marked. In the case where the boundary is accurately represented on the ground by improvements such as a fence, then a single reference mark is to be placed on the intersection of the surveyed line with the improvement.
- Placement of one reference mark exactly on line, line produced, or half angle is recommended. Intermediate marks are required at 500 metre intervals or at other distances necessary to maintain line of sight. Reference marks and intermediate marks are to be sunk at least 0.3 metres where ploughing or other disturbance is likely.
- Posts are to be stamped with ‘E’ as viewed from inside the easement. It is preferred that each post is stamped with a unique identifier and the reference to that identifier is shown in the field notes and included on the easement plan.
- Trenching of posts will not be necessary but the use of a steel fence dropper, star picket or similar, positioned adjacent to each post as a marker is recommended where such placement does not endanger stock, people or property.
2.3. Field Notes
The field notes of the survey must be lodged in a standard cadastral field book certified by a licensed surveyor holding a current practising certificate.
Where GPS is used, the survey must be recorded in the field book as specified in Landgate’s current Survey and Plan Policy and Procedure Guides.
2.4. The Plan
The ‘Interest Only’ Plan should be drafted as generally indicated in Landgate’s current Survey and Plan Practice Manual.
Traverses from geodetic stations to the easement must be shown on the Plan, not necessarily to scale.
If the survey is mostly based on GPS surveys, the Plan should bear the following statement – ‘Dimensions derived from GPS observations’, but expanded to show the appropriate detail, for example ‘RTK’.
3. Easements by Calculation from the SCDB
3.1. General Provisions
The ground definition and marking of the boundaries of many easements that protect public and private assets such as pipelines or powerlines by normal survey methods is expensive and, in terms of physical identification and spatial accuracy, generally unnecessary.
3.2. Procedure
3.2.1. Spatial Upgrade
If the area of interest has not been spatially upgraded arrangements can be made for the spatial upgrade to be performed by the surveyor.
Additional geodetic connections would normally be required to achieve a suitable spatial accuracy of the upgraded SCDB.
3.2.2. Spatial Accuracy
In general, a nominal accuracy of 0.5 metres in rural and pastoral areas and 0.1 metres in urban areas for the upgraded SCDB is required to achieve an adequate degree of positional certainty.
If the area has been spatially upgraded but not achieved the aforementioned accuracies, additional geodetic connections will be necessary.
The geodetic connections should be in accordance with Section 4
3.2.3. Spatial Extent of Easement
If the infrastructure has already been constructed, a survey to determine the geographic position of all the physical elements that need to be contained within the easement must be carried out.
This ‘as-constructed’ survey must provide positions that are compatible with the boundary definition.
The aim is to achieve certainty that the structure falls completely within the easement. This would mean that a margin of error depending upon the expected relative accuracy is allowed when determining the clearance between the structure and the boundary.
The easement dimensions are calculated within the spatially upgraded SCDB to completely enclose the existing infrastructure, based upon the ‘as-constructed’ position. Intersections with other land boundaries are also calculated and shown on the plan.
If the infrastructure has not yet been constructed, then the easement dimensions are calculated within the spatially upgraded SCDB in accordance with the requirements of the owner of the asset to be protected. Sufficient survey control and marking is required to accurately define the easement at any time in the future.
3.2.4. Spatial Verification
The SCDB is a digital cadastral model that has been constructed from a limited number of surveyed connections between cadastral marks and State geodetic stations.
An estimate of the spatial accuracy of any point in this model can be given by a statistical analysis of the least square adjustment results. This is expressed in the SCDB as the ‘circular error’ (arithmetic mean of the major and minor semi-axes of the error ellipse).
The accuracy of this estimate can be tested by comparing the positions of a set of surveyed boundary points that have not been included in the adjustment with the modelled position.
The method of survey and the accuracy of measurements shall be such that there is less than a 5% probability that the actual error in position of any surveyed boundary point within the area of interest exceeds the accuracy statement for that point in the SCDB.
Verification can be achieved by making redundant geodetic connections to cadastral points within the area of interest that are not used in the spatial upgrade process. These can be used to verify the reliability of the adopted geodetic connections, and to provide a ground truth for upgraded points in the SCDB.
The field notes of the survey, including geodetic connections, pickup of the infrastructure and ground truthing connections, must be in a standard cadastral field book certified by a licensed surveyor holding a current practising certificate.
Where GPS is used the survey must be recorded in the field book as specified in Landgate’s current Survey and Plan Policy and Procedure Guides.
3.2.5. The Plan
The ‘Interest Only’ Plan is to be drafted in accordance with the requirements of Landgate’s current Survey and Plan Policy and Procedure Guides.
The following additional notations are to be placed within the graphic area of the Plan:
- Surveyed in accordance with Survey Practice Guidelines for Easements under regulation 26A of the Licensed Surveyors (Guidance of Surveyors) Regulations 1961’.
- ‘Dimensions derived from the Spatial Cadastral Database as at <date of final adjustment/calculation>’.
- ‘Calculations have been made on the GDA94 and distances reduced to mean ground level’.
- ‘Easement boundaries are completely unmarked but related to the SSMs shown’.
- The notation ‘Reg 26A’ is to be added to the ‘approved’ panel in the title block.
4. Geodetic Connections
4.1. Survey
For each connection provide, sufficient data to enable MGA coordinates to be derived for at least two points on a cadastral alignment. Where practicable these points should be separated by 200 metres or more.
Locate and validate existing cadastral points. Marks must be renovated or replaced in accordance with the requirements of the Licensed Surveyors (Guidance of Surveyors) Regulations 1961. Additional reference marks are to be placed at cadastral points occupied with GPS.
Validate the horizontal stability of the controlling SSM from reference marks.
Survey the connection using the following technique:
- observe a GPS baseline between the controlling SSM and one cadastral point, and
- observe a GPS baseline between the selected cadastral points. Note that it is not acceptable to calculate a connection between the cadastral marks on the basis of individual GPS observations from the controlling SSM.
Where practicable, provide redundant measurements that will confirm the connection.
The GPS baseline observation may be of any type (static, rapid static, kinematic) as long as the required precision is achieved.
4.2. Accuracy
Horizontal ground distances and azimuths as calculated from GPS observations between the selected cadastral points should agree with original values within the limits specified in the Licensed Surveyors (Guidance of Surveyors) Regulations 1961. Where such agreement is not attained then further pickup is recommended to prove the alignment.
The method of survey and accuracy of measurements shall be such that there is less than a 5% probability that the actual error in the positional accuracy (co-ordinate) of the cadastral mark with respect to the SSM will exceed r millimetres provided by the formula:
r = c(d + 0.2) - where d is the direct distance between the two points in kilometres and c is as specified in Table 7.1 below.
4.3. Field Notes
For GPS baselines, both the ellipsoidal (GRS80) and mean ground level distances and the calculated mid-azimuths are to be clearly documented in the field book. Also to be recorded is the angle, as calculated from end azimuths between the SSM connection and the re-established alignment (or offset).
MGA coordinates are not generally to be shown in field notes as they are subject to change should any readjustment of the controlling SSMs be undertaken. However, a listing of the base station input coordinates and the cadastral points and their derived MGA coordinates is required in the case of a GPS RTK survey.
Details of the GPS hardware type including serial numbers of receivers and antennae plus the software version used for reduction of observations must be recorded on the index page of the lodged field book/s together with calibration details for EDM and bands, if used.
Sufficient information should be recorded to demonstrate that the required accuracy has been achieved.
To facilitate cross referencing it is important that the following details are clearly shown in the field notes for each connection:
- Original (Orig) distances between the GPS connection point and adjacent cadastral bends or corners
- Lot `numbers, road names or numbers, reserve numbers, etc.
- Clear details of the search used including the page number/s of field book/s together with details of the field book/s containing the centreline or ‘as-constructed’ survey
- Survey Index Plan reference.
5. Transmission Line Easements
5.1. Scope
These guidelines are applicable to the following two situations of determining the spatial definition of transmission line easements:
- by local re-establishment and calculation, and
- by calculation from the Spatial Cadastral Database (SCDB).
The survey methods for each of the above situations will be similar, but there will be some data transfer processes to consider if calculating from the SCDB.
No ground marking of easements for transmission lines will be required. These guidelines are applicable to easements over both Crown and Freehold land.
5.2. Local Re-establishment and Calculation
5.2.1. General Provisions
It is the surveyor’s responsibility to ensure that the survey method used is appropriate for the circumstances, and that the work is proven.
Survey methods should conform to the basic principles of survey as defined in the Licensed Surveyors (Guidance of Surveyors) Regulations 1961.
To facilitate verification of the survey and integration with the SCDB, rigorous connections to the State Geodetic Survey (geodetic connections) are required. In remote areas a surveyed connection should be made to each geodetic station within 10km of the transmission line. In areas with a greater density of geodetic stations, geodetic connections should be made at intervals of not more than 5km. The geodetic connections should be in accordance with Section 4.
Where GPS is used the survey must be carried out in accordance with Landgate’s current Survey and Plan Policy and Procedure Guides.
5.2.2. Field Notes
The field notes of the survey must be lodged in a standard cadastral field book certified by a licensed surveyor holding a current practising certificate. The following information is to be recorded in the field book:
- Normal requirements of cadastral re-establishment.
- Validation of SSMs from reference marks.
- All connections from SSMs to cadastral points.
- Any additional control placed and connections from that control to cadastral points whether measured or calculated.
- Marking and referencing details with relevant abutting information (e.g. lot on plan, C/T, road name).
- Feature information (e.g. fences, terrain, access).
- Any other relevant information.
It will not be necessary to include all the easement dimensions in the field book.
5.2.3. The Plans
The plans should be drafted as specified for ‘Interest Only’ Plans in Landgate’s current Survey and Plan Practice Manual. The Plan type will be ‘Freehold’ and the purpose will be ‘Interest’.
Each Plan must be compatible with the easement documents that the Service Provider intends to register. The extent of each plan must be consistent with the proposed registration actions of the Service provider such that upon registration of the documents, the whole of the plan can be approved.
Surveyors need to consult with the Service Provider as to the registration requirements. Where any uncertainty exists surveyors should prepare individual easement plans for each affected parcel.
CSD files based on MGA coordinates are to be prepared in accordance with the requirements specified by the Inspector of Plans and Surveys for each individual Plan and lodged at Landgate.
Where the survey is based on GPS observations, the relevant Plans should bear the following statement:
“Survey dimensions derived from GPS observations.”
The following notations are to be placed within the graphic area of the plan:
“Surveyed in accordance with Survey and Plan Practice Guidelines for Transmission Line Easements under regulation 26A of the Licensed Surveyors (Guidance of Surveyors) Regulations 1961.”
“Reg 26A” is to be added to the approved box in the title block.
6. Calculations from the SCDB
6.1. General Provisions
A method that satisfies the key factors of certainty of position (within adequate tolerances) and reasonable cost is a calculation of the easement boundaries using Landgate’s Spatial Cadastral Database (SCDB). This method relies upon the spatial relationship of the physical infrastructure with the boundaries defined in the SCDB.
The SCDB must be spatially upgraded using the surveyed easement alignment and/or control traverse before definition of the easement can be undertaken. Areas of the SCDB that are upgraded for this purpose must be done in accordance with Landgate’s requirements. Definition of easements by calculation from the upgraded SCDB can only be accepted where the accuracy of the SCDB is sufficient to provide certainty of position within adequate tolerances. (See Section 4.2.)
6.2. Procedure
In the case of existing transmission lines a survey to determine the position of all the physical elements of the infrastructure that need to be contained within the easement must be carried out. For new lines where easement definition is required prior to construction a centreline survey is necessary.
This survey must provide positions that are compatible with the boundary definition. The aim is to achieve certainty that the structure falls completely within the easement. This would mean that a margin of error depending upon the expected relative accuracy is allowed when determining the clearance between the structure and the boundary.
The easement dimensions are calculated within the spatially upgraded SCDB to completely enclose the existing infrastructure based upon the surveyed position. Intersections with other land boundaries are also calculated and shown on the plan. See Section 3 for other provisions that apply to transmission line easements.