Question

A flagpole appears in two successive photographs taken at an altitude of 2,000 m above datum. The focal length of the camera is 120 mm and the length of the air base is 200 m. The parallax for the top of the pole is 52.52 mm and for the bottom is 48.27 mm. Find the difference in elevation between the top and the bottom of the pole.
1. 55 m
2. 44.2 m
3. 67 m
4. 30 m
5. 50 m

Answer 1

Correct Answer - Option 2 : 44.2 m

Concept:

The difference in elevation (∆h) = \(\left( {\frac{{{{\rm{p}}_1} - {{\rm{p}}_2}}}{{{{\rm{P}}_1} \times {{\rm{p}}_2}}}} \right) \times {{\rm{B}}{\rm{f}}}\)

Where,

p1, and p2 = Parallax for the top and bottom respectively, B = length of airbase, and f = focal length of the camera.

Calculation:

Given: Parallax for the top = 52.52 mm, Parallax for the bottom = 48.27 mm, B = 200 m, and F = 120 mm

∆h = \(\left( {\frac{{52.52 - 48.27}}{{52.52 \times 48.27}}} \right) \times 200 \times 120\;\) = 44.2 m