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Author Topic: AERIAL ARCHAELOGY  (Read 1511 times)
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Posts: 41646

« on: July 10, 2008, 06:21:42 pm »

An image of Cawthorn Camps is compiled by mapping

Image mapping

How then, is the archaeology mapped from all this photography? All photographs, obliques and
verticals, are digitally rectified to remove inherent distortions, due mainly to height and camera
tilt, and transformed into corrected plan views.

The accuracy of the resultant photo-map is largely dependent on the accuracy of the control that
the photo is rectified against, usually Ordnance Survey maps and height data, at 1:10,000 or 1:2,500 scale. For the highest possible accuracy, new vertical photography of the site is taken using a calibrated camera, and control is surveyed on the ground.

A computer software programme automatically generates height information, by comparing adjacent photo frames (remember that overlap?), and a composite orthophoto (a photo-map accurate to a few centimetres) can then be produced to the desired scale (see the image of Cawthorn camp). This is made possible through the use of a device called a stereoscope.

'The Victorians had stereoscopes in their parlours and bought views of famous places to marvel at.'
Stereoscopy involves two photographs, vertical or oblique, taken in close succession, each frame capturing a slightly different view of the same subject. They can be viewed stereoscopically, using no props, to recreate in the mind's eye a 3-d model of the landscape - or you can use a stereoscope to make it easier.

The Victorians had stereoscopes in their parlours and bought views of famous places to marvel at,
and the 'magic eye' craze of a few years ago worked on the same principle.

A stereoscope, at its simplest, is a pair of lenses mounted on a folding stand and costing less than 30. The device helps make it easier to see earthwork archaeology on vertical and oblique photographs, as things appear to 'stand up' out of the photo. Anyone interested in this process can take their own 'stereo pairs' of photographs on the ground. After taking one photo, you just take a couple of steps to the side and take a second photo.

Try it next time you are out with a camera.

The only tricky part is learning how to view them if you don't have a simple stereoscope, but it isn't impossible.
« Last Edit: July 10, 2008, 06:25:05 pm by Bianca » Report Spam   Logged

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