Land Survey Introduction
The process of carrying out large scale land survey by photogrammetry has been revoltionised in recent years with the availability of commercial UAV that produce accurately geo-tagged images along with software algorithms for pattern recognition that have removed the need for human correlation of data. The output of aerial land surveys can be issued as three types of data.
orthomosaic data
Orthomosaics are made up a series of aerial photographs taken in nadir (looking directly down on the earth) format that are then stitched together. The algorithms used to process the data also eliminate parallax error so that the resulting image appears flat and without distortion. The output is accurate to +/- 30mm and equivalent to a land based CAD survey.
elevation maps
Elevation maps are a graphic representation of the relative height of the land. They can be calibrated to OS height data or merely used as a graphic representation of topography to support other data outputs referred to below.
point cloud or dxf output
Point clouds are files that contain the co-ordinates of millions of points of data output as either .xyz or .las files. This enables desktop computers to recreate the land geometry in third party applications such as AutoCAD Civil 3D. Output of contours as DXF Files can also be incorporated into land modelling software or represented as 2D drawings in CAD based software.
