Orthophotos and True Orthophotos plus DSM

Orthophoto
A digital orthophoto (in short DOP) is a true to scale visualisation of the earth’s surface. For the un-distortion of the vertical images a digital terrain model is used. Depending on the size of a project up to several thousand images are geometrically and radiometrically homogenized and mosaicked.

True Orthophoto and DSM
For true orthophotos a digital surface model (in short DSM) is used for un-distortion. The DSM is created by stereoscopic image matching. It represents the image surface of visible terrain, infrastructure and vegetation. For a 10 cm ground solution this corresponds to 100 points/m².

Comparison Orthophoto and True Orthophoto
In “regular” orthophotos tumbling of the images is a common phenomenon which appears with e.g. multi-storey buildings particularly in edge areas. When overlaying these images with cadastral maps, differences between the maps are clearly visible. In True Orthophotos on the contrary not only near-ground objects are depicted correctly but also multi-storey buildings and engineering structures like tunnels and bridges.

Advantages of True Orthophotos
• No tumbling of images
• No distortions in engineering structures
• High resolution DSM