Test Your EQ (Engineering Quotient)

EQ #3

A 15-megapixel consumer-grade digital camera is being used for aerial photography. The lens being used on it gives it a 22° horizontal (cross-track) field of view. When flying at 10,000 feet above the ground, what is the approximate per-pixel resolution?

Handheld cameras typically have aspect ratios between 1.2 and 1.5; let’s assume this one has a ratio of 1.33 (i.e., equivalent to 640 × 480). That means that the sensor has about 4,470 pixels horizontally and 3,360 pixels vertically.

22° divided by 4,470 is 0.00492°, or 85.9 µradians. Since sin(x) = x for small angles, we can just multiply the height by the angle in radians to get the resolution: 0.859’ or 10.3”.


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