Horizontal Datum - orientation

Note: this guideline is issued by the Surveyor-General under section 7(1)(ga) of the Cadastral Survey Act 2002 about the Rules for Cadastral Survey 2010 and is not legally binding.

The following information relates to the orientation of horizontal bearings on a cadastral survey, including ways that orientation may be obtained or verified.

Bearings must be NZGD2000 where a new primary parcel boundary point is created

A survey which defines a new primary parcel boundary point must orientate all bearings in terms of the applicable official geodetic projection.  This will always be the NZGD2000 Meridional Circuit projection in which the cadastral survey dataset is situated.

Referto Ruling on official geodetic datum and projections (LINZR65300)

As well as being internally consistent with other bearings on the survey, all bearings must be correctly orientated in respect of the meridian (within the accuracy standards in rule 3) [r 4.1]

Bearings for covenant and non-primary parcels under rules 16 and 17

A survey which defines a new covenant in terms of rule 16 (Alternative requirements for covenant parcels) or rule 17 (Alternative requirements for non-primary parcels) must orientate all bearings, other than existing magnetic bearings, in terms of the applicable geodetic projection [r 16.4(a) and r 17.1(d)(ii)].

Obtaining and 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 accurate orientation (within the accuracy standards in rule 3),
  • observing some or all lines using GNSS technology (refer to Bearings from GNSS below),
  • obtaining an orientation from a previous CSD (refer to further information below).

Existing NZGD2000 bearings may not be adequate

The bearings on some existing NZGD2000 surveys may not have been accurately obtained.  Surveyors will need to carry out sufficient work to ensure that the bearings derived from existing NZGD2000 surveys are in terms of the local NZGD2000 projection [r 4.1].

Where a difference in orientation exceeds the applicable accuracy standards, an adjustment to the existing bearings may be required and reported on [r 8.2(a)(ii) and (iii)]. 

NZDG1949 bearings and NZGD2000 bearings may not be the same

Although the datum orientation for NZGD1949 and NZGD2000 is virtually the same, the bearings on some existing NZGD1949 surveys have not been accurately obtained.  Surveyors will need to carry out sufficient work to ensure that the bearings on these existing NZGD1949 surveys are in terms of the local NZGD2000 projection [r 4.1].

Where a difference in orientation exceeds the applicable accuracy standards, an adjustment to the existing bearings may be required and reported on [r 8.2(a)(ii) and (iii)].

Bearings from GNSS

Orientations derived by GNSS can be determined directly in terms of the official geodetic datum independently of the orientation of existing surveys and old marks in the locality.

The practice of adjusting GNSS derived bearings to be in terms of existing surveys and old marks in the locality creates a risk that the final orientation will not be in terms of the required datum and projection.

Bearings from three origin marks

It is no longer a rule requirement to obtain a bearing origin from three existing marks.  The Rules do not specify an 'origin of bearings' and a surveyor may use any method they consider adequate to ensure their survey orientation meets the requirements of rule 4.1.

A theodolite can be used to carry forward an existing orientation based on observations between existing marks.

Surveyors should note that this orientation is dependent on the accuracy of the previous survey or surveys.  In the absence of control network marks or where existing surveys daisy-chained off each other, an accumulation of small errors in bearings often resulted in the orientation of such surveys being in terms of their origin marks, but not in terms of the purported datum or projection.

Testing bearings from three origin marks

Where orientation is obtained from existing marks, there are a number of ways that surveyors can test that their bearings are in terms of the meridian.  Examples include:

  • observing from a mark 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 far enough apart to take into account the effects of coordinate inaccuracies,
  • examining the chain of previous surveys (and possibly survey reports) to validate the original orientation's reliability.

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

Bearings where boundaries are not marked

Rule 4.1 applies irrespective of a new primary parcel boundary point being marked or unmarked.

Last Updated: 6 April 2017
Authority: Surveyor-General - Section 7(1)(ga) of the Cadastral Survey Act 2002
LINZ OP G : 00080