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A new close-range three-dimensional photogrammetry program has been introduced. This one uses digital images on a computer screen instead of standard photos on a digitizing tablet. Photographs may be taken with a digital camera, or prints or slides may be digitized. In either case, the points to be surveyed are selected from the digitized images on screen.
There are significant advantages to using digitized images. The orientation of the images is easier, and, once an image has been oriented, it can be used again and again without re-orienting it. Photos on a digitizing tablet, however, must be oriented each time they are used.
Digitized images also remove the enlarging process from the equation. That is an aid to accuracy, since the enlarger can add distortion to the image that cannot be easily corrected.
In one sense, digitized photos are less expensive; there are no enlargements to make. On the other hand, the computer files are enormous; so the disk space required can be very expensive indeed.
The most significant drawback for digitized images remains the quality of the images themselves. Only a very high-resolution digital image can provide the kind of accuracy required for archaeological surveying; so only the more high-tech forms of digital imagery will be useful. Nonetheless, this is a promising technology, and developments in digital imagery will make it very useful in the long run.
Next Article: Digital Inclinometer for Historic Architecture
Table of Contents for the August, 1994 issue of the CSA Newsletter (Vol. 7, no. 2)
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