Real Time Kinematic - a form of corrected GPS giving accuracy down around 20 mm. Requires sophisticated kit (cost usually >£10 000) and more advanced training for the operator. A great part of Ordnance Survey`s large-scale topographic data collection is carried out by RTK GPS. Essential ingredient is an RTK quality signal from an external source. ... Found on http://www.encyclo.co.uk/local/20475