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For a reconnaissance survey, it is necessary to obtain vertical aerial photographs of a terrain at an average scale of 1:13000 using a camera. If the permissible flying height is assumed as 3000 m above a datum and the average terrain elevation is 1050 m above the datum, the required focal length (in mm) of the camera is

1. 100
2. 150
3. 125
4. 200

Correct answer: 150

Solution

The required focal length can be calculated using the formula that relates scale, flying height, and terrain elevation. With a flying height of 3000 m and an average terrain elevation of 1050 m, the effective flying height becomes 1950 m. Using the scale of 1:13000, the focal length is determined to be 150 mm, which is consistent with the given parameters.

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