Photogrammetry is the technique of extracting three dimensional detail points from two dimensional photographs.

In the simplest example, the three dimensional coordinates of points on an object are determined by measurements made in two or more photographic images taken from different positions. Common points are identified on each image. A line of sight can be constructed from the camera location to the point on the object. It is the intersection of these rays (triangulation) that determines the three-dimensional location of the point.

The photography can be flown by fixed wing aircraft, helicopters or be ground based or terrestrial photogrammetry for buildings or structures.

The aerial photography is tied together and related to a survey grid on the ground by photo control points; usually coordinated by a network of GPS observations.

The deliverables of a photogrammetric survey can be the discreet coordinated points, CAD line drawings, or the ortho-rectified photography itself. Ortho-rectified images are created by scaling and removing any distortion from the original site photos. They can also be transformed onto the site survey grid to enable overlay with conventional DXF data and dimensions to be measured directly from the images.

Photogrammetry can provide an ideal cost effective solution in a number of situations:

• A large area can be covered rapidly resulting in reduced time in the field
• Complex and controversial land access problems can be avoided
• There are Health and Safety benefits from a remote survey
• Costly rail possessions, road or lane closures can be avoided
• A value added dataset (orthorectified photography) is produced
• A photographic archive for monitoring or future mapping can be created.

We can advise on the achievable accuracies and whether this could be the solution to your needs.

Example applications include:

• Conventional 3D mapping and production of ‘ortho-rectified images’
• Route proposals for tram and train lines
• Terrain models (DTMs) for flood modelling
• Surveying for new roads
• Telecoms mast installations
• Pipeline routes

Aerial LIDAR Survey:

Helicopter LIDAR (Light detection and ranging) is another from of Aerial mapping - this time by direct measurements. LIDAR measurements create a ‘point cloud’ of non-intelligent 3D survey points (see image). These points are dense enough to observe between trees and on the tree canopy – creating a versatile data set over large areas of land.

LIDAR is ideal for visual impact analysis, route planning or surveys covering large areas of land, especially where access to the land is an issue.

See the Generic Services page for case studies in Photogrammetry and LIDAR.

For advice on organising or specifying an Aerial survey, call us or e-mail webenquiry@severn-partnership.co.uk for advice.