The vertical datum relationship grids allow the transformation of local vertical datum heights to NZVD2016. These grids have been calculated using geodetic control marks which have both an ellipsoidal and normal-orthometric height for each local vertical datum.
A significant aspect of the New Zealand Vertical Datum 2016 (NZVD2016) is the relationships between the national vertical datum and the 13 local mean sea level datums, or Vertical Datum Relationship Grids.
For NZVD2016 the transformation from each local vertical datum is modelled by a grid, allowing the offset value to vary depending on horizontal position. This is different to the approach used for NZVD2009 where datum relationship was represented as a single value offset.
The datum relationship grid is designed to cover the area where LINZ hold marks within a single local vertical datum. The grids are published at a 2 arc minute spacing (approx. 3.6 km).
The grids were computed using a ‘best fit method’, meaning that the grid is not forced to pass through the values at the observation points. Parameters allowed a point error of 1mm and a distortion error of 0.5ppm.
The grids were populated with the differences between the ellipsoidal and normal-orthometric heights at high order geodetic control marks (both orders 0-5 and 1-2V), and tends toward the mean datum relationship value in areas where there are no control points.