Unit 2: Orthophoto maps

Orthophotos and Orthophoto maps

• Orthophotos are made from vertical aerial photos

• Orthophoto maps are made by adding map information to the orthophotos

  • They have contour lines placed over them to provide a sense of the height of the landscape

• An orthophoto map is a combination of a map and a photo

• An orthophoto map has a larger scale than a topographical map

  • Topographical - 1cm : 50 000cm

  • Orthophoto - 1cm : 10 000cm

• Since 2008 a digital mapping camera has been used to make orthophoto

  • When this camera is flown over an area, the images are recorded and corrected for scale automaticaly

Vertical Aerial Photographs

• Photographs captured from the air by a large camera that is fixed to the floor of an aeroplane which is flying directly over the photographed landscape.

• The camera axis is vertical to the ground (90-degree angle).

• Vertical aerial photographs show a top view of the landscape, its settlements, landforms and other features.

• These photographs are usually filmed and printed in black and white to save costs, but they can also be filmed and printed in colour, electronically.

• Vertical aerial photographs have a larger scale than topographic maps.

  • This means that features on these photographs are larger than map features.

• Vertical aerial photography helps to map large and inaccessible areas.

Types of Vertical Photographs

Contour Lines on Orthophoto Maps

• Orthophoto maps show a digitally changed image of the ground, as though every feature is seen from directly above

• In reality, aerial photograph images captured by a camera are distorted or skewed by the lands shape and by the position of the camera

• In addition to orthophoto images correcting the distortion they also provide height cues by having contour lines placed over the image