Providing & Verifying Orientation

Orientation in terms of NZGD2000

The Rules for Cadastral Survey 2010 require all surveys that define or mark a new primary parcel boundary, and that make a new field measurement, to be oriented in terms of a NZGD2000 projection.

Ruling LINZ R65304 provides a temporary exemption from this rule and alternative requirements for some surveys until 24 May 2011.

As well as being internally consistent with other bearings on the survey, all bearings must be correctly oriented in respect of the meridian within the accuracy standards in rule 3.

Obtaining & proving orientation

Reliable orientation can be obtained by several methods including:

  • observing orientation lines into the survey from control marks
  • calculating orientation from cadastral survey network marks located at a sufficient distance to provide an orientation meeting rule 3 accuracy standards (eg by a resection or by a ray trace calculation)
  • observing some or all lines using GNSS technology
  • obtaining an orientation from a previous CSD (see next paragraph).

Obtaining an orientation from a previous CSD usually consists of finding a traditional ‘origin of bearings’ based on three old marks from a previous CSD. However, such orientations may not always be sufficiently accurate in terms of the meridian. In rural areas in particular, inaccuracies may have resulted from errors creeping in through successive ‘daisy chained’ surveys, or from inaccurate corrections being applied to orientations in terms of other datums. Where orientation is obtained from a previous CSD there are a number of ways that surveyors can test that their bearings are actually in terms of the meridian. These include, for example:

  • observing from marks on the survey to a cadastral survey network mark at a suitable distance from the survey and comparing the observed bearing with a bearing calculated from coordinates
  • connecting the survey, either by measurement or by adoption, to two or more cadastral survey network marks and comparing the surveyed bearing with a bearing calculated from Landonline coordinates. When making this comparison, the marks used should be at sufficient distance apart to provide an orientation meeting rule 3 accuracy standards
  • examining the chain of previous surveys (and possibly survey reports) to validate the reliability of the original orientation (eg some old NZGD1949 coordinated control marks that may now have NZGD2000 coordinates will allow comparative joins to be calculated).

The tests should verify that the bearings are in terms of the meridian within the tolerances specified in the accuracy standards. The tolerances apply across the whole of the survey and therefore the most critical test is between the marks furthest apart.

Reporting orientation

The basis for determining the orientation of bearings and the accuracy of that orientation must be included in the Survey Report (rule 8.2(a)(ii) and (iv)).

  • Where control marks or cadastral survey network marks have been used to calculate an orientation, the fit with check lines should be reported. The fit with any lines from previous CSDs that are in terms of the same datum should also be reported.
  • Where GNSS has been used to obtain orientation, a statement about the proper use of the technology and the checks that have been applied will suffice. The fit with any lines from previous CSDs that are in terms of the same datum should also be reported.
  • Where orientation is obtained from a previous CSD, a good method is to provide a calculation sheet for any check rays such as to cadastral survey network marks. Showing these comparisons on a calculation sheet rather than capturing them in Landonline prevents scale problems when generating the diagram of survey. However, where the survey is required to connect to a cadastral survey network mark by rule 4.2 those connecting vectors must be captured. Any validation of the orientation through the chain of previous surveys can also be provided in the Survey Report.
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