Vertical Offshore Reference Frames
Vertical Offshore Reference Frames (VORF) is a set of high resolution surface models, published and maintained by the UK Hydrographic Office, which together define a vertical datum for hydrographic surveying and charting in the United Kingdom and Ireland. Tidal surface models The following tidal and sea level surfaces are included: Chart Datum (CD) Lowest Astronomical Tide (LAT) Mean Sea Level (MSL) Mean Low Water Springs (MLWS) Mean High Water Springs (MHWS) Highest Astronomical Tide (HAT) Land datums including Ordnance Datums Newlyn, Belfast and Poolbeg The surfaces are modelled with respect to the terrestrial reference frame used for satellite navigation (GNSS) positioning, ETRS89. Thus VORF directly permits the use of high precision GNSS in hydrographic survey, and also allows the capability of transforming vertical data between the different datums. The UK Maritime & Coastguard Agency requires the use of VORF for tidal reductions as part of its civil hydrography programme. Files A main product of the VORF project was the gridded vertical correction files which deliver the capability to transfer heights and depths from one vertical reference system to another, "allowing the direct use of depth data from surveys which is referred to a WGS84 compatible datum rather than Chart Datum