Question

The scale of an aerial photograph is 5 mm = 100 m. The size of the photograph is 23 cm × 23 cm. If the longitudinal overlap is 65% and sidelap is 20%, the number of photographs required to cover an area of 12.5 km × 8 km is __________________ (in integer).

Hint:

When calculating the number of photographs required, account for the overlap in both longitudinal and lateral directions to find the effective ground coverage.

Answer 1

Correct Answer: 36

The scale of the photograph is given as \( 5 \, \text{mm} = 100 \, \text{m} \), or \( 1 \, \text{mm} = 20 \, \text{m} \).
The size of the photograph is \( 23 \, \text{cm} \times 23 \, \text{cm} \), which is equivalent to \( 230 \, \text{mm} \times 230 \, \text{mm} \).
Thus, the ground coverage of one photograph is: \[ \text{Ground coverage} = 230 \, \text{mm} \times 20 \, \text{m} = 4600 \, \text{m} \, \text{or} \, 4.6 \, \text{km}. \] Now, account for the longitudinal overlap of 65% and sidelap of 20%. The effective ground coverage is: - Longitudinal coverage: \( 4.6 \, \text{km} \times (1 - 0.65) = 1.61 \, \text{km} \) - Lateral coverage: \( 4.6 \, \text{km} \times (1 - 0.20) = 3.68 \, \text{km} \) To cover an area of \( 12.5 \, \text{km} \times 8 \, \text{km} \), calculate the number of photographs required: \[ \text{Number of photographs} = \frac{12.5}{1.61} \times \frac{8}{3.68} \approx 36. \] Thus, the number of photographs required is 36.