During spring ‘leaves off’ periods at a flying height of 15,000 ft. with a 6 inch mapping camera with forward motion compensation. The scale of the photography is therefore 1:30,000.

Aerial Triangulation (AT) block models were developed and tested for accuracy. Adjacent blocks are tied to new ones to insure a ‘seamless’ image. DTM data points were collected on analytical stereoplotters at a sufficient density to support generation of 3 meter contours conforming to the National Map Accuracy Standards (+ or - 1.5 meters). Mass points were collected along parallel scan lines 75 meters apart at variable density as a function of the topography and other ground features. Spot elevation at summits and in depressions and breaklines along significant linear features were also collected. Distinctions between ‘hard’ and ‘soft’ breaklines were established and standardized to facilitate the generation of contours.

The photography was scanned at 15 microns and the images were differentially rectified using the DTMs and the AT block models. The histogram for tonal adjustment provides for a range of gray shades from 30 to 225 ( out of 256), thus allowing pure black and white to be legible when overplotted on the images. Accuracy of the image was given precedence over tonal consistency at the edges of the images. The final digital images were clipped with the Orthophoto Index Grid, thus the tiles do not overlap. The images meet or exceed the National Map Accuracy Standards to the extent that 90% of the well defined features fall within 0.5 mm of their true position on the ground at the nominal output scale of 1:5000 (2.5 m on the ground). Additionally, the maximum displacement of well defined features is less than 5 meters. Each pixel in the digital orthophoto image represents 0.5 meters on the ground. ..."

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