GPS (Global Positioning System) is a surveying tool that
A D Horner Limited use primarily on topographic surveys when the client requires either the land survey to be adjusted to the Ordnance Survey National Grid
Co-ordinate system, or to Ordnance Survey level datum.
For most developments GPS is not necessary and we would not advise the additional expense. However if the scheme is a more major development then it is most likely that relating the topographic survey to the OS National Grid will be required.
Sometimes there is a requirement for the land survey to be related to the Ordnance Survey level datum by GPS rather than using the historic benchmark datum, especially on larger schemes or where there is a flooding risk.
As wonderful as GPS is there are several limitations to it's use;
- To get a good 'fix' a GPS system really needs to be set up for a minimum of four hours, the longer the system is left in position, the more satellite passes are made, the more accurate the fix.
- GPS is not as accurate as a conventional total surveying station and this is particularly true in level.
- Whilst GPS can speed up the topographic survey of large open spaces, it cannot be used under tree canopies or in the shadow of buildings where there is no ‘open' sky to get a satellite fix. This means that other traditional methods have to be used to fill the gaps in the survey, which slows productivity down.
- Real Time Kinematic GPS (RTK) relies on being able to get a mobile phone signal.