Guest blog by OS Surveyor Lee Harvey.
Imagine you’re buying a new house and are worried about the risk of flooding. Or you’re installing a mobile network, such as 5G, and want to know where to place transmitters. You’ll need to know the shape of the ground, buildings blocking line of sight, where will water flow, and a host of other things. OS create a set of 3D height products as well as our 2D maps and data.
Remote Sensing at OS is a big thing. The team spends Spring and Summer (when the weather is better… apparently!) flying up and down Great Britain capturing aerial imagery. These images are used to update our maps quickly and efficiently at head office in Southampton. By taking many overlapping images and using some air triangulation software (that’s the maths of measuring angles from the air), we match these images to their real-world location and work out the height of features on the ground. The software takes these height points and constructs a Digital Surface Model (DSM), which also forms the basis of our orthorectified imagery (a top-down perspective, map-like image). The DSM data includes buildings, trees, bridges and anything which exists at the time the photos are taken. A video game is a good example, as you move your character through any 3D environment, the hard surface that the game graphics display, will be draped over a DSM (although it’s called a Mesh in the 3D graphics industry, the fundamentals are the same). To complement this surface, and to allow lots of clever analysis of the real world, we also create a Digital Terrain Model (DTM).