Can I install my own height bench marks on the Newlyn datum?
A. Yes. The services available on this web site allow you to compute high-accuracy orthometric heights (mean sea level heights) relative to the Ordnance Survey height datum without visiting any Ordnance Survey bench marks, and without knowing in advance the orthometric heights of the control stations you use. Ordnance Datum Newlyn (ODN) is the usual definition of mean sea level on the British mainland and some islands. Any survey station with precise ETRS89 GPS coordinates determined using the National GPS Network can be used as a height bench mark by obtaining the equivalent orthometric height from the Ordnance Survey National Geoid Model OSGM02 (this is available from this web site in the Coordinate converter’ service). It is advisable to use several such stations on the same site and level between them, to check the consistency of the orthometric heights. There is no need to occupy traditional Ordnance Survey bench marks by GPS, unless you have a specific requirement to check the re
