# NZGD1949 Orders

New Zealand Geodetic Datum 1949 (NZGD1949) is a horizontal datum so coordinates in terms of it are two-dimensional.

NZGD1949

Horizontal coordinates in terms of the NZGD1949 are classified into horizontal orders according to the type and standard of observations that were used to determine them. A numerically lower order generally implies a more reliable coordinate.

A mark may have coordinates in multiple geodetic and vertical datums with different Orders in each.

The following table describes the NZGD1949 Orders. A description of the NZGD1949 observations standards is described in the next table.

OrderDescription
1Coordinates derived from the original NZGD1949 adjustment in 1949 that defines the datum. The observations meet the 1st order observation standards
2Coordinates derived from adjustments of observations of 2nd order observation standards connecting to 1st order marks
3Coordinates derived from adjustments of observations of 3rd order observation standards connecting to 1st or 2nd order marks
4aCoordinates from 2nd or 3rd order control downgraded because of poor design, high density, substandard ground marking, large adjustment corrections or non-compliance with 2nd or 3rd order specifications.
4bCoordinates supplied by LINZ District Office or LINZ contractors from modern reliable survey fix with proven origin and observation specifications (benchmark coordinates derived from urban or rural geodetic control surveys, trig coordinates derived from photo control surveys)
4cCoordinates determined by a hanging line fix over 100m long from a 1st, 2nd or 3rd order station or benchmarks with geodetic coordinates obtained from unknown sources
4hNZGD1949 coordinates obtained by double entry table transformation from initial coordinates in terms of the Hawkes Bay 1931 datum (post-Napier earthquake)
6aOld cadastral datum coordinates converted to NZGD1949 by double entry table transformation
6bCoordinates obtained by scaling from maps
2d, 3d, 4dCoordinates calculated in terms of NZGD2000 and subsequently transformed to NZGD1949.

These coordinates may be inconsistent with surrounding NZGD1949 coordinates as they were often measured from remote marks using GPS. The transformation modelled some of the distortion in the NZGD1949 datum, but it cannot represent all local effects.

NZGD1949 'd' coordinates are also described on this site.

### NZGD1949 Observation standards

The NZGD1949 datum is largely derived by adjustments of triangulation (horizontal angle) data. The following minimum standards were required for deriving 1st, 2nd, and 3rd order coordinates.

OrderTriangle ClosureLength ClosureNumber of Sets
MeanMax
11"3"1 in 25,00012
23"5"1 in 10,0006
35"8"1 in 5,0003