OSTN97: ETRF89 Referenced OSGB

This projection is specifically used to convert between ETRS89 and Ordnance Survey^® British National Grid using the OSTN97^® transformation. The National Grid Transformation OSTN97 is an interpolated grid of horizontal plane shift parameters covering GB at 1-km resolution, which converts ETRS89 GPS coordinates to National Grid coordinates with an accuracy of 20 cm (RMS). It takes no projection-specific parameters.

Note: Users should not normally have to use this projection to define their own systems – FME ships with the OSGB-GPS coordinate system, which is based on this projection.