The GATE Grind

GATE 2022 CE (CE1) – Question 23

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

An aerial photograph is taken from a flight at a height of 3.5 km above mean sea level, using a camera of focal length 152 mm. If the average ground elevation is 460 m above mean sea level, then the scale of the photograph is

  1. 1 : 20000
  2. 1 : 20
  3. 1 : 100000
  4. 1 : 2800

Practise this question in The GATE Grind →

Show answer and explanation

Correct answer: (A) 1 : 20000

Explanation

Photograph scale is focal length divided by flying height **above ground**. Here $H-h=3500-460=3040$ m and $f=0.152$ m.

Thus $s=0.152/3040=1/20000$. **Answer: 1:20000 (A)**. Using height above mean sea level directly would omit ground elevation.