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GATE 2024 CE (CE2) – Question 30

Geomatics Engineering · Photogrammetry: scale, flying height, parallax, camera calibration · 1 mark · Multiple choice

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

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Correct answer: (B) 150

Explanation

The scale of a vertical photograph is $\frac{f}{H - h}$. The flying height above the average terrain is $3000 - 1050 = 1950$ m. So $f = \frac{1950}{13000} = 0.15$ m $= 150$ mm.