The Digital Terrain Model (DTM) is a bare earth model, posted at 5m with a vertical accuracy of less than 60cm RMSE (root mean square error). The model represents the bare ground surface without any objects like trees and buildings. The dataset covers Great Britain. The first surface model, the Digital Surface Model (DSM), which represents the earth’s surface including all objects on the surface, is produced using the digital stereo aerial photography acquired by Getmapping. The DSM is edited to produce a 5m DTM product. A suite of algorithms have been applied to semi-automatically edit the DSM and remove unwanted surface features such as buildings and vegetation. These algorithms include a routine which reduces the woodland canopy areas based on a bounding polygon. This requires some manual intervention to create bounding polygons for woodland extents and identify true ground level. In addition, break lines are captured where required to ensure true terrain features are not removed and that bodies of water, such as lakes, remain flat. The PGA Elevation data offers improved spatial resolution compared to the NEXTMap data. The data is from the Pan Government Agreement (PGA) and an in-perpetuity license has been granted to BGS. The data is being managed by the Earth and Planetary Observation and Monitoring (EPOM) Team in support of the wider BGS Programme.
