An area 45 km long and 36 km wide is to be photographed to an average scale of 1:12000, using an aerial camera of f = 21 cm. The speed of the aircraft is 200 km/h. The photographs are 23 cm square, with a longitudinal overlap of at least 60% and lateral overlap of 30%, average elevation of the terrain is 500 m above MSL. Calculate the following:

• The flying height above mean sea level (MSL).
• Distance between successive exposures
• Distance between flight lines for successive strips.
• Flight line spacing on flight map at a scale of 1 cm = 600 m
• Interval between successive exposures
• Number of photographs per strip taking one extra photograph at either end
• Number of strips with only one extra strip as a safety factor
• Total number of photographs

• The flying height (H) can be calculated by using

• Spacing of the flight line (W)

• Number of flight lines (N _fl ) required

• Actual spacing between flight lines

• Spacing of the flight lines on a flight map

• Ground distance between exposures

• Exposure interval

Since required overlap is at least 60%, hence exposure interval can be kept as 19 seconds.

• Adjusted ground distance between exposures
  L = 55.55 x 19 = 1055.45 m

• No. of photographs per flight line (N _p )

Allowing two extra photographs at each end, the total photographs per flight lines = 44 + 2 + 2 = 48.

• Hence, total no. of photographs = 48 x 20 = 960