Oblique Aerial Photographs are Photographs taken at an angle. If they are taken from a low angle earth surface–aircraft, they are called low oblique and photographs taken from a high angle are called high or steep oblique. The technical definition of the vertical aerial photograph is photography looking down on a subject at an angle of less than or equal to three degrees from the vertical. In other words, the vertical aerial photograph is defined as an aerial photography technique where the shots are taken from directly above the subject of the image
The following are advantages of oblique aerial photograph over vertical aerial photograph:
- Oblique aerial photograph may use inexpensive cameras because they are not used for photogrametric or precision purpose.
- Determination of feature elevations is more accurate using oblique aerial photograph than vertical aerial photograph.
- An oblique aerial photograph covers more ground area than vertical aerial photograph taken from the same altitude and with the same focal length.
- If an area is frequently covered by cloud layer, it may be too low and/or impossible to take aerial vertical photograph but there may be enough clearance for oblique coverage.
- Oblique aerial photograph have more natural view because we are accustomed to seeing the ground features obliquely. For example tall objects such as bridges, building towers and others will be more recognizable because the silhouettes of these objects are visible .
- Objects that are under tree or under other tall objects may not be visible on vertical aerial photograph if they are viewed from above. Also some objects such as ridges, cliffs, caves and others of the same reflection may not show on the vertical aerial photograph if they are directly beneath the camera.