Positioning and measurement
Positioning and measurement
This domain tests whether you can obtain, reduce and report positions in New Zealand's geodetic framework. Expect NZGD2000, NZVD2016, NZTM2000, PositioNZ/continuous GNSS, static and RTK GNSS, traverses, levels, least-squares adjustment, and the difference between precision and accuracy.
Core rules and concepts
- Work in a stated reference frame and epoch; NZGD2000 coordinates change with tectonic deformation.
- NZTM2000 is a projection: ground distances must be converted with a combined scale factor before comparison with grid coordinates.
- GNSS requires clear sky, good satellite geometry, correct antenna height and redundant observations.
- RTK solutions need independent checks; a small reported uncertainty is not proof of absolute accuracy.
- Leveling and trigonometric heighting must use the correct vertical datum and account for curvature/refraction where relevant.
Worked example
A ground distance of 100.000 m is measured between two points. The combined scale factor for the location is 0.999600. Grid distance = 100.000 × 0.999600 = 99.960 m. If a design coordinate difference is 99.960 m, the ground distance is consistent. Reporting 100.000 m as the grid difference would create a 0.040 m error, which matters for setting out and for checking a GNSS baseline.
Traps
Using ground distance as grid distance; ignoring scale factor or convergence; entering the wrong antenna height; mixing NZGD2000 and local coordinates; treating an RTK fix as an accuracy guarantee; and failing to check a baseline with an independent method.