Summer services update
The International Terrestrial Reference Frame (ITRF) is a dynamic datum. Its coordinates change with time, and the datum has many different versions (or realisations). This means that an accurate transformation using ITRF is only possible with a reference date. This is usually stored as the coordinate epoch.
International Terrestrial Reference Frame (ITRF)
When you are calculating a coordinate transformation that includes a dynamic datum, additional parameters are needed to account for the time-dependent transformation and its deformation model/distortion grid. These provide the parameters for the internal deformation of the datum.
When New Zealand Geodetic Datum 2000 (NZGD2000) was developed it was aligned with the International Terrestrial Reference Frame 1996 (ITRF96), at the reference epoch 2000.0 (the date of 1 January 2000).
New Zealand Geodetic Datum 2000 (NZGD2000)
New Zealand has distorted since January 2000, including deformation due to significant earthquakes.
Coordinate transformation
The LINZ online coordinate converter uses the following processes to transform coordinates from ITRF to NZGD2000, or vice versa.
To transform a coordinate from ITRF to NZGD2000:
- Convert the ITRF coordinate to the ITRF96 realisation (for example, if the coordinate is in the realisation ITRF2008, it must first be converted to ITRF96).
- Subtract the value from the NZGD2000 model at the date of the coordinate epoch.
To transform a coordinate from NZGD2000 to ITRF:
- Calculate the NZGD2000 deformation value at the specified date and add it to the ITRF96 coordinate.
- Convert the ITRF96 value to the required ITRF realisation.
For more information on transformations between ITRF realisations and NZGD2000, including equations and examples, see the help document.