CivilForge

Photo Scale

S = \frac{f}{H} = \frac{d _{map}}{D _{ground}}

Vertical-photograph scale S (representative fraction) is focal length over flying height above ground. Equivalently, a length on the photo divided by the same length on the ground. Relief displacement and tilt distort scale away from the nadir; use H − h_terrain for variable terrain.

S

Photo scale (RF)

f

Focal length

H

Flying height above datum/ground

d, D

Photo length and ground length

Step-by-step solved example

Camera f = 152.4 mm, flying height above ground H = 762 m. Find the photo scale.

Similar triangles: map scale S = f/H.

1. Units
f = 0.1524 m, H = 762 m.
2. Scale
S = 0.1524/762 = 1/5000.
$S = 1/5000$

Answer: S = 1:5000

10 practice questions

0/10 correct

1.f = 6.00 in, H = 3000 ft. Scale is

2.Larger flying height (same f) makes the scale

3.A road 250 m long measures 50 mm on the photo. Scale is

4.Relief displacement on a vertical photo is radial from the

5.Stereo overlap along the flight line is typically about

6.If terrain is 200 m above datum and flying altitude is 1200 m above datum, use H_agl =

7.Photo distance 20 mm represents 100 m on the ground. RF is

8.Wide-angle mapping cameras have relatively

9.Scale 1:24 000 means 1 inch on the map is

10.Tilted photographs have a scale that