FIN2023N2000 geoid model

The FIN2023N2000 is a quasigeoid model (height conversion surface) of Finland. The model is recommended to be used inside of the Finnish borders as well as in the territorial waters of Finland. The model contains quasigeoid heights, ζ, that are used to convert EUREF-FIN ellipsoidal heights, h, to normal heights, H*, in the national height system of Finland, N2000.

Quasigeoid heights in the FIN2023N2000-model are given in meters with millimeter accuracy. Evaluating the model with the ground truth in Finland (first order GPS-levelling dataset), an accuracy of ±1.38 cm was achieved nationwide. The largest quasigeoid height differences between the FIN2023N2000-model and GPS-levelling are 3–4 cm.

To transform heights between the systems, one must first find the four points from the geoid grid that are nearest to the geographical EUREF-FIN coordinates of the point that is to be transformed. I.e., which four points close the point in question inside of a rectangle. Next, quasigeoid height of the transformed point is calculated with bilinear interpolation using the four grid points. Finally, normal height is calculated by deducting the quasigeoid height from the EUREF-FIN ellipsoidal height (H* = h - ζ).

The FIN2023N2000 is available in three ASCII-formats (box, grid and list). The dimensions of the model with grid spacings are given in the first row (header) of the box and grid -files. Values of latitudes and longitudes are given in degrees. Dimensions are the following:

| **Attribute** | **Value** |
|---|---|
| Minimum latitude | 58.80° |
| Maximum latitude | 70.19° |
| Minimum longitude | 19.00° |
| Maximum longitude | 31.98° |
| Latitude spacing | 0.01° |
| Longitude spacing | 0.02° |
| Total number of points | 741 000 |