Figure 2-7. Tick Marks Representing

Matching Detail at Nadir.

NOTE: See Figure 1-4 for an explanation of the scan angle.

2. There are two ways to determine ground coverage vertical to the flight path. One way is

that the altitude above ground level (AGL) or H-h in ft equals the approximate ground

coverage in m. To obtain a more accurate measurement, multiply the tangent (Tan) value of

one half the scan angle (

) of the imagery. Your answer will give you ground coverage for

one half of the imagery in ft or m, depending on the measurement you are using. For

example, H-h = 2,000 ft and half the scan angle (

) = 60. You must first use the

trigonometric functions (trig) table (Figure 2-8) to convert 60 to its Tan value, which is 1.7320.

Next, you must multiply 2,000 x 1.7320 = 3,464 ft, which covers 1/2 a flight line width,

multiplied by 2 = 6,928 ft; to obtain m, divide 6,928 by 3.281 and you have 2,112 m of total

coverage. Using the following formula:

Tan 60 x (H-h) x 2

Ground coverage =

3.281

Ground coverage =

1.7320 x 2 000 ft x 2 = 2,112 m.

3.281

NOTE:

In most cases, missions will be flown straight and level. But, on occasion it may not

be practical.

3. For additional information of trig functions, study subcourse IT 0684, panoramic

photogrammetry.

43

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