SPP-12 Three Dimensional Plans
Version 1 - 18/07/2018
1 The Cubic Parcel
The guidelines in this chapter are for the survey and drafting of Plans that include three dimensional lots (i.e. lots limited in height or limited in depth other than by the traditional Crown Grant depth limit). These Guidelines do not apply to plans under the Strata Titles Act.
Except when structures define the intended boundary surfaces vertical planes should be used in the definition of the 3D lot as much as possible. In the absence of other restrictions, definition of the lot parcel by horizontal and vertical plane (not curved) surfaces is preferred for simplicity of description. The inclusion of curved edges or surfaces is discouraged but if these are necessary, single or compound circular curves may be used. Spiral or other transition curves are unacceptable.
When defining upper or lower boundary surfaces by means of reduced levels (and unless following a constructed surface) the boundary surfaces must be a series of plane surfaces. Twisted planes are not acceptable because they are not unique. An infinite number of different twisted planes can all pass through the same four non-planar points.
When a boundary plane is defined by four or more points (the usual situation), those points must be calculated to be planar. If this is not the case the boundary surface must be broken into two or more planes, by recording changes of grade or by introducing break-lines on the Plan. Plan example 38 shows several such break-lines.
If the corners are not closely marked in three dimensions, then in the case of urban areas (and especially inner urban and city areas where complex three dimensional surveys are becoming frequent) the survey method and the accuracy of the survey should be at least equivalent to those specified for Special Survey Areas under General Regulation 26A, with nearby connections to the geodetic network in three dimensions.
It is recognised that the development methods and the boundary relationship to physical structures will vary greatly between different developments. But the density of marks and of connections to physical structures must correlate with the critical nature of the boundaries and correlate with the high value of the land. It is not acceptable to simply reduce the marking because it is physically impossible to mark most of the corners. Alternatives must be used (possibly unique to each case).
The sources of the AHD datum for the survey should be recorded in the field book.
Three dimensional boundary corners should be marked directly if practicable. Otherwise a mark should be placed on a vertical edge of the parcel (or its production), on a horizontal or sloping edge or least satisfactorily as an offset mark related three dimensionally to the corner of the lot. In the case of indirect marking it may be preferable to only record the mark in the field book (ie as an RM).
It is accepted that it will not be possible to mark or reference those three dimensional corners of the lot which are either high in air space or deep within construction material or earth. In those cases an alternative should be found, for example connections to the structure.
4 Location of Structure
A connection to a wall shown on a plan makes that wall a monument and monuments have precedence over measurements. Thus the recording of the position of the structure in relation to the boundary is a prudent practice for the surveyor to establish the intention, apart from the benefit to future surveyors in facilitating re-establishment.
Showing connections to horizontal surfaces of the structure could be particularly relevant in the re-establishment of a horizontal boundary surface defined via a long levelling traverse.
In the case of ‘below ground’ structures it is recommended that sufficient connections be made to the structure and recorded in the field book, to allow the relationship of the boundaries to the structure to be proven, to reduce the risk of mistakes and to provide an examination trail.
5 What Must be Shown on the Plan
The Plan must show all of the dimensions of each of the lots and other land tenure (roads etc.) and of the surround of the Plan. These dimensions include the definition of heights in the case of three-dimensional parcels.
The Plan must show abuttals (tenure and plan numbers) in all three dimensions (ie including tenure above and below the lot, and above and below the new Plan). The horizontal abuttals should show all of the abutting tenure at different heights where applicable. A Plan view and at least one other view or alternative means should be used to clearly define each three dimensional lot.
These guidelines are not intended to restrict or standardise. They are designed to help surveyors and to reduce delays in processing. The first priority is to make the survey Plan clear and complete – by whatever means you can devise. It is expected that three-dimensional Plans will be used for increasingly more complex lots (and easements) in the future.
7 The Plan View
The Plan must include a Plan view as the primary view. It is recommended that you show on the primary Plan everything that can be shown on that view without getting too cluttered. This includes all horizontal angles and distances that are at the surface of the ground and lot numbers and abuttals. This may require one or more enlargements – still in Plan view, and may need a second sheet.
It is very desirable that the primary Plan view also record (probably without dimensions, and just in outline) the position of below ground and ‘at height above ground’ parcel boundaries. It is suggested that these outlines use a new line symbol (0.35mm dots spaced at 3mm, used also for Mines boundaries) to differentiate from easement boundaries, road secants, break lines etc.)
It is recommended that each below ground and ‘at height above ground’ lot be recorded on a separate Plan view which shows its Plan dimensions. The height dimensions may be recorded on this view in simple cases. It can be impossible to find the space to show on the crowded main Plan the various lot numbers at different heights.
In such a case it is recommended that the main Plan shows only the numbers or names of those parcels which are unlimited in height. Then a separate enlargement can be drawn for lots which are limited in height or depth, showing on the enlargement a key for each polygon, linked to an adjacent schedule recording the key adjacent to a listing of the tenure at different heights.
In simpler, less crowded situations the statements could be put directly on the main Plan view.
8 Options for Defining Vertical Limits
Following are several suggested options for defining the upper and lower limits of three-dimensional lots:
- A simple stand-alone statement quoting reduced levels – for simple flat and horizontal surfaces. See plan example 37, and the example in the table 21.1.
Table12.1: Definition of vertical limits of the various tenures in the Murray Street Mall
|Polygon Key Shown on Plan.||Tenure||Upper and Lower Limit of the Tenure|
Above RL 31
Between RL 31 and RL 22.5
Between RL 22.5 and RL 17
Between RL 17 and RL 7
Below RL 7
Above RL 31
Between RL 31 and RL 7
Below RL 7
Above RL 31
Between RL 31 and RL 15
Between RL 16 and RL 7
Below RL 7
- A statement using point numbers on the Plan linked to a schedule showing the point numbers and the associated reduced level for each. This can be used for sloping planes but needs extra clarification when any point number has two or more upper limits (or two or more lower limits) associated with it, usually a step in the surface. See plan example 35 and plan example 39.
- A vertical elevation or a vertical section can be used to illustrate steps clearly. See plan example 38.
- An isometric projection to scale can illustrate more complex shapes. It is generally best to only show one lot per isometric projection. See examples on plan example 38. If, because of the viewing angle points or lines on different surfaces coincide on the view, causing confusion, it is acceptable to show the projection as ‘not to scale’ and then stretch the graphic so as to separate the co-incident points or lines. Usually this is only practical near the edges of the view.
Where several three dimensional parcels abut or interlock it is acceptable to use a vertically exploded isometric projection. This will separate the parcels to allow each to be shown clearly, but also defines how they all fit together. See plan example 38.
Whether separate enlargements or elevations are used for each parcel or whether they are combined to save space is a decision for the surveyor. Both are acceptable, provided clarity is achieved.
9 Defining Upper and Lower Limits of 3D Lots
Always use reduced levels above Australian Height Datum to define the upper and lower limits of three-dimensional lots. AHD heights should be recorded on the Plan to the nearest 0.01 metre. In a vertical elevation or isometric view the practice of showing a reduced level along a horizontal line is favoured.
The traditional format of showing depth limits on Plans (e.g. ‘limited in depth to 12.19 metres’ - carried forward from the Crown Grant) is misleading on three-dimensional Plans, all of which carry a reference to AHD. It is recommended that on three-dimensional plans, the full wording of the depth limit from the Title is used (ie ‘………12.19 metres below the natural surface of the ground’).
Because extensive ground disturbance may be a part of the development relating to a three dimensional Plan, it is recommended that if the natural surface or remnants of it, are visible at the time of survey that its height be measured and recorded in the field book for future reference. In complex cases it is very useful to show an approximate height of the ground or paving at selected places on vertical elevations or isometric views – to clarify the situation to the viewer (as on plan example 38, 39, 68, 95 and 105.)
Some structures may approach or reach the depth limit, in which case the surveyor may elect to convert the depth limit to AHD reduced levels and to record that lower surface as part of the graphic. This is acceptable but because of the risk that there was cut or fill many years ago, it would be prudent to qualify those RLs – for example ‘nominal depth limit is 2.70 metres above AHD, for information purposes only’.
10 Isometric Projections
‘Statutory’ Plans are used:
- To facilitate actions under various statutes in reference to particular areas of land. They do not affect tenure but impose conditions or lift constraints on the subject of the Plan.
- For ‘Notices of Intention to Take’.
- For administrative boundaries and these boundaries can be of a temporary nature exempting an area for 1 day from restrictions under law that would not allow the proposed activities to take place. Examples of a more permanent nature include definitions of Port Authority areas, custom areas, off-road vehicle areas, shire and rating area.
- Where the nature of the administrative process does not justify the expense of survey and marking.
11 Areas of Three Dimensional Lots
An area should be shown for each lot. In the case of three-dimensional lots the shapes of lots can vary greatly, so a range of methods may be necessary. These may include:
- As first priority it is recommended that the area recorded be the area at ground level.
- If the above is misleading, the area of the bulk of the lot could be recorded.
- If the lot is wholly or predominantly below ground level:
- the area at below ground level should be shown, or
- in some cases where there are gross differences in area at different heights it will be useful to record more than one area for a lot, calculated at representative heights and recorded as such.
- The height at which the area of each three dimensional lot is calculated should be shown (unless it is obvious)
In the past some lots which were closed in height and depth have been annotated with a cubic volume instead of an area. It is now thought that this is an added complication with little benefit so it is recommended that only areas be shown in future, not volumes.
12 Total Area of Plan
It is not necessary to show the total area of the subject land on the Plan except for Crown surveys. Refer Plan Practices Section 15
13 Easements Limited Vertically
For easements (typically under section 136C of the Transfer of Land Act) limited vertically, similar methods should be used as are used for descriptions of parcel boundaries, with the notable difference that no marks are necessary for easement boundaries. See plan examples 35 and 36. In the case of multiple three dimensional easements within a building (easements for a variety of purposes) the situation can be complex and it is then recommended that each easement be drawn on its own enlargement, usually a Plan view with the third dimension defined by reduced levels. See plan examples 35 and 36. In some cases a vertical elevation or isometric projection may be needed as well.
In some situations of overlapping or abutting easements, it will be advisable to draft a vertical elevation or vertical section depicting the relationships among the various easements (for example in the case of access and service easements passing through a dividing wall or party wall). See plan example 36.
14 Digital (CSD) Files
Vertical information is not required in the Cadastral Survey Data (CSD) file for three dimensional lots. The horizontal extent of each three-dimensional lot and easement must be recorded in the CSD file (and also that of the Plan surround). On some Plans this can result in two, three or several lots populating the same SCDB space (but at different heights). This is acceptable and will be clarified by the viewer referring to the Deposited Plan.
All that is required for the CSD entry for each three dimensional lot is a horizontal outline or ‘footprint’, not all of the intricacies of the lot boundary at different heights. It is suggested that the most informative footprint is the total extent of that lot but it is recognised that this may not always be practical and that an alternative such as the lot extent at ground level may sometimes be better.
There is no firm rule – the purpose is to illustrate and to guide the viewer to the Deposited Plan for the rigorous solution. Two dimensional easements are recorded in CSD files. Three dimensional easements should also be recorded in CSD files but only in Plan view. The 3D button within the lot identification should be activated.