The following information relates to rule 3.3.1 and the accuracy requirements for boundary points on right-line and arc boundaries that are defined on a cadastral survey.
In summary, the accuracy standard specifies two tiers of accuracies:
- a more stringent level of accuracy to be met between 95% of new and old points (a 95% confidence level) [r 3.3.1, Table 2(i), (iii), and (v)], and
- a less stringent level of accuracy to be met by all points (100%) [r 3.3.1, Table 2(ii), (iv), and (vi)].
These accuracies differ depending on whether the boundary points are classes A, B, or C.
The following information explains these requirements in more detail.
The more stringent tier requires the survey to provide 95% likelihood (confidence) that the relationship between the marks specified in the Rules meets the specified accuracies. This 95% standard applies to all new work but not to adopted work. The standard uses the root sum squared (RSS) method to calculate the accuracy value [r 3.3.1(a)(i), (iii), and (v)].
This second tier is less stringent with tolerances approximately 50% greater than the more stringent standard.
The standard requires the relationship between all (100 %) of the points specified in the Rules, including all adopted points to meet the specified standards. The standard uses a simple sum method to calculate the accuracy value [r 3.3.1(a), (ii), (iv), and (vi)].
This means that up to 5 % of the relationships between new work are permitted to be outside the more stringent accuracy standard providing they are within the less stringent standard.
For new and old boundary points, the accuracy tolerance remains at about 0.04 m for points up to 100 m apart.
For new and adopted boundary points, the tolerance increases from 0.06 m at a steady rate of 0.015 m per 100 m.
For new and old boundary points, the tolerance approximates 0.20 m for points up to 150 m apart and increases steadily as marks get further away.
For new and adopted boundary points, the tolerance increases from 0.30 m at a steady rate of 0.06 m per 100 m.
Confidence levels can be estimated through a least squares analysis and are influenced by the number and location of the vectors connecting the points (the strength of the geometry) and the accuracy of those vectors. Good survey practice, strong geometry, accurate measurement, and the inclusion of additional non-boundary vectors may provide assurance the required confidence levels are met.
Note that where circuits include new and adopted vectors, the circuit closure may not be a definitive indicator of meeting the confidence levels because of the different accuracy specifications in rule 3.3.1.
The accuracy tolerances apply to all horizontal and vertical boundaries and all their associated boundary points that are on a parcel being surveyed.
The affected points include:
- adjacent points on a boundary line,
- all points on the same boundary line,
- points not directly joined by boundary lines,
- points on intersected boundaries where the severed existing boundary is being replaced by two new shorter boundaries,
- a non-primary parcel boundary point and an underlying parcel boundary point; for example, an easement boundary point and an associated primary parcel boundary point.
Accuracy tolerances do not apply to adopted boundary vectors that:
- are not between boundary points on parcels being created on the survey, and
- which are used for the purposes of boundary definition (in the same manner as poor quality traverse vectors are permitted to be used as evidence in locating an existing boundary point [r 3.1,Table 1(b)].
This is illustrated in Figure 3 above (in green).
Adopted boundary vectors used for the purposes of boundary definition must be included in the Diagram of Survey [r 9.6.13(d)]. If these vectors do not provide a fit within applicable accuracy standards between reliable survey marks on the survey, there will usually be a conflict that needs to be resolved and boundary points to be defined by survey.
Details of any conflict and how it was resolved, and details of decisions relating to boundaries defined by survey must be included in the survey report [r 8.2(a)(v) & (ix)]. Calculation sheets and diagrams can greatly assist with illustrating this information. When used, they must be included in the CSD and referred to in the survey report [r 8.2(b)(i)].
The computed boundary vectors between boundary points on parcels being created on the survey, resulting from resolving the conflict, must comply with the accuracy standards.
Note that the capture of adopted boundary vectors used for the purposes of boundary definition, where they fit poorly with other data captured in the CSD, will generate Landonline pre-validation adjustment report test failures. An assessment of actions taken to address these failures is required to be included in the survey report (Lodgement Standard 7).
The boundary accuracy tolerances specified in rule 3.3.1 do not apply to the relationship between boundary points where the boundary points are on parcels that are not contiguous with other parcels being surveyed.
Where a rural parcel abuts an urban area and adopts existing boundaries that are class A, the class A boundaries must comply with the applicable class A accuracy standards [r 3.3.1(a)(ii)].
Providing these boundaries are not being marked and meet the class A accuracy tolerances, they may be defined by adoption (the requirement to define by survey under rule 6.2(a)(iv) only applies to the boundaries of a parcels under survey).
For new boundaries of covenants, the use of class C may be used where class B boundaries would normally be required (refer to Alternative requirements for covenant parcels (rule 16)).
Where a new non-primary parcel's boundaries are unable to be determined accurately in terms of the underlying parcel boundaries a field survey may be required with the placement of witness marks and PRMs (refer to Alternative requirements for non-primary parcels (rule 17)).
When the accuracy class of a primary parcel boundary is upgraded upon resurvey:
- an existing non-primary parcel boundary that intersects with that primary parcel boundary may need to be defined to that higher accuracy class [r 3.3.1]. Refer to Class of boundary point
- all existing non-primary parcel boundaries must meet the same accuracy standard as the primary parcel boundaries [r 3.3.1]. The exception to this is where the boundaries of the non-primary parcel, when created, were permitted to be of a lesser accuracy standard and that lesser standard is still permitted. An example is an existing covenant surveyed pursuant to rule 16 (Alternative requirements for covenant parcels) where boundaries were permitted to be class C and a class C boundary may remain providing the underlying parcel boundary is class B.
This exception does not apply to non-complying non-primary parcel boundaries that were originally permitted by specific dispensation. A dispensation applies only to the survey being carried out at the time a dispensation was provided. A subsequent surveyor must reconsider the issues afresh and either resolve the issues or seek a further dispensation.
There is no provision for allowing boundary vectors of new parcels to be adopted where they fail the current standards and only meet the survey accuracy tolerances in place at the time of the original survey. Where the criteria of classes C and D are not applicable, the inaccuracies must be resolved.
For adopted boundary vectors that are not associated with the parcel under survey, refer to Boundary points that the right-line and arc boundary accuracy tolerances apply to above.
Historically, there was often no difference in the accuracy of 'traverse' vectors and boundary vectors as boundaries were often traversed. Adopted boundary vectors were therefore usually used for the purpose of defining a boundary position. This may no longer be suitable as the boundary accuracy standard for boundary vectors [r 3.3.1] is less than the survey accuracy standard [r 3.1].
To reliably re-establish a boundary position, the network of non-boundary marks will normally provide the most accurate solution.