Description:
RAF18 is a hybrid geoid model for France, covering the area 42° < lat < 51.5°, -5.5° < lon < 8.5° with a grid spacing of 1.5' in latitude
and 2' in longitude. It is an update of the previous RAF09 model. In particular it is an adaptation of the QGF16 model to 10000 high
accuracy GNSS/levelling points. The RAF18 model represents the height of the IGN69 reference surface above the GRS80 ellipsoid (RGF93 datum).
It has been assessed by using 5000 independent GNSS/levelling points, showing differences with a standard deviation of 1 cm. RAF18
was an intermediate solution that was consistent with RGF93, while RAF18b is the final and official solution that is consistent with RGF93b, where the transformation between the two frames is a Helmert 7-parameter transformation
References:
IGN (2018). Comment obtenir des altitudes NGF – IGN69 ou IGN78 à partir de levés GPS?.
Laboratoire de Recherche en Geodesie, Service de Geodesie et de Métrologie.
IGN (2019). National Report - France. EUREF Symposium 2019, 22-24 May 2019, Tallinn, Estonia.
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