Survey control marks
Every attempt is made to keep the survey mark information in the ACTmapi Survey Infrastructure Map up-to-date. We welcome feedback and advice on the condition and accuracy of survey marks.
Trig Stations (MC)
Identifier: district names, old surveyors' names, for example, Tennent, Goodwin.
Today's trig stations consist of a ground mark with a white quadripod supporting a black disc above the ground mark. Most of these Trig Stations are part of the ACT Precision Zone, a national geodetic survey and adjustment carried out in the early 1970s. The ACT Precision Zone and its associated marks have been the primary control for all new development in the ACT since the early 1970s. The accuracy of ACT Precision Zone marks is 1 in 250,000.
Sectional Control Marks (SC)
Identifier: two alpha plus 1, 2 or 3 numerals, for example, TG116
These marks are fixed directly from the ACT Precision Zone at about one kilometre intervals. They usually consist of a deep driven rod protected by yellow concrete posts. Some Sectional Control marks are beaconed (for example, YA90, TG84). The accuracy of Sectional Control marks is 1 in 100,000.
Subdivision or Neighbourhood Control Marks or "RMs" (SRM)
Identifier: three numerals, for example, 363
These marks are fixed from the Sectional Control at intervals of between 200 and 400 metres. They usually consist (on placement only) of a galvanised pipe set in concrete protected by two steel droppers painted red and white. There may be an aluminium tag with the mark's identifier either set in the concrete of the mark or wired to one of the steel droppers. The accuracy of Subdivision Control is 1 in 30,000.
The subdivisions in Woden Valley (early 1960s) were the first to have Subdivision Control. In suburbs constructed before Gungahlin (pre-1990), Subdivision Control marks were 50 to 100 metres apart. Some of these marks survived development and can be found in open spaces in the suburbs. Only those SRMs in Gungahlin have been entered in the Survey Control Mark Detail Database Control Base. Information on others is contained on plans.
Coordinated Reference Marks or CRMs (CRM)
Identifier: CRM plus numerals - starting at 1 eg. CRM7381
In today's subdivisions numbered CRM plaques are placed in the kerb and coordinated by survey traverses that start and finish on Sectional or Subdivisional Control marks or other previously coordinated CRMs. These marks are about 50 to 150 metres apart. Only subdivisions constructed after 1980 contain CRMs that appear on Deposited Plans. Most do not have a height attributed to them.
Many CRMs have been placed in the older suburbs of Canberra in recent years. These CRMs were coordinated using GPS and are on the AGC system, which is not the system of the surrounding subdivision. Since 16 April 1998 a new style of CRM is used that has a raised nipple for accurate levelling. These are numbered from 10,001 and up.
SR (Steel rod) Marks (SR)
Identifier: SR plus numerals - starting at 1 eg. SR1003
The ACT Government Survey Office places SR marks in new subdivisions - one for every 100 blocks. The mark consists of a deep driven steel rod contained within a small manhole marked "Survey mark". These SRs are included in the CRM traverses and are precise levelled. Many other SR marks have been placed throughout Canberra. Most are coordinated on the AGC system which may not be the coordinate system of the surrounding subdivision. Not all SR marks are levelled. Conversely, some SRs have been levelled, but are yet to be surveyed for co-ordinates.
Kerb Bench Mark (KBM)
Identifier: KBM plus numerals - starting at 1, for example, KBM5203
Kerb Bench Marks are placed in the kerbs throughout urban Canberra. They consist of a rectangular brass casting with a nipple and number. Distance between KBMs in new suburbs is 100 to 200 metres and levelling is to 3rd order accuracy. (Many kerbs have moved and differences of more than 3 centimetres have been found). All KBM levels are on the Australian Height Datum (AHD). Precise Bench Marks (PBMs) are listed in the KBM register under their number (for example, PBM13 is KBM13). PBMs are precast concrete blocks that were part of earlier Imperial levelling network on an earlier Canberra datum: Precise Datum or PD. (To convert PD reduced levels (feet) to AHD (metres), subtract 1.07 feet from the PD value, then multiply the result by 0.3048 to give the AHD value).
Rural Bench Marks (RBM)
Identifier: RBM plus numerals - starting at 1, for example, R376
Rural Bench Marks were placed in the 1970s, at half mile - one kilometre - intervals, along many roads in the ACT. They consist of a star-iron picket driven to its full length into the ground and surrounded by a concrete collar containing a brass plaque with the mark's identifier. One yellow concrete post may be protecting it. In recent years many of these marks have been coordinated from GPS surveys. Other rural bench marks with identifiers "P", "NE", "NW" and "C" can be found on roads in the ACT. Not all have level (AHD) values.
Photo Control Marks (PC)
Identifier: One alpha plus thee numerics.
Photo Control marks consist of a G.I Pipe in concrete protected by a wood post painted red and white. Many Photo Control marks are for "level only" and their accuracy depends on the scale of the photography they are controlling.
Alpha Marks (AM)
Identifier: Three alphas - starting at AAA
Alpha Marks usually consist of a GI Pipe in concrete protected by two steel droppers. They are usually placed as a control mark for a specific survey - usually an engineering survey. The accuracy of these marks depends on the nature of the survey they are part of. Many are of an accuracy that does not warrant nominating the coordinate system.
Miscellaneous Marks (MS)
Identifier: not specified
Miscellaneous marks are any mark not contained in the previous categories (apart from Recovery marks). Some examples are old radial blocks, control marks placed before Sectional Control series commenced, dam deformation marks.
Identifier: RM plus numeral plus mark it recovers (for example, RM2 Painter)
Recovery Marks are close to more important marks.