3. Flight Planning

a. Considerations

Generally multiple aerial photos will be needed to cover an area. Depending on area configuration, more than one flight line may be necessary. A number of factors affect how many photos are needed, primarily flying height, focal length, negative/image size, and side/endlap percentages. Their combination affect the neat model's ground converage. Knowing the neat model and area sizes, the number of photos and flight lines can be determined. 

b. Ground Coverage

Scale relates photo area to ground area. This is shown in Figure E-7 and quantified in Equations E-1 and E-2.

Figure E-7 Neat Model Ground Area

		Equation E-1
		Equation E-2
	l	negative/image side length
	S	Scale

Refeing to Figure E-3 and recalling that the neat model extends halfway into the sidelap area, the width of the neat model is the same as the distance between the fight lines, W. 

Using the previous neat model example, with a 6.0 inch focal length camera flying 1200 ft above terrain, ground coverage is:

The flying height can be increased if greater coverage is needed. Otherwise a different camera can be used, varying focal length and image format size combinations. 

 c. Flight Lines

A flight line consists of two or more consectutive neat models. Multiple flight lines are uiformly spaced, W, to ensure there are no gaps betweeen adjacent neat models, Figure E-8.

Figure E-8 Adjacent Flight Lines

The optimum flight line orientations and number of photos can be determined by comparing the neat model ground coverageto to the approximate dimensions of the area to be mapped.

Continuing with the example, the area to be mapped is roughly rectangular, approximately 3500 ft N/S and 4750 ft E/W, Fugure E-9.

Figure E-9 Area To Be Flown

.

 Figure E-10 shows that three E/W flight lines cover the area. 

Figure E-10 E/W Flight Lines

There are seven neat models per flight line, requiring 8 photos.

The total number number of photos needed is (3 lines) x (8 photos/line) = 24 photos

Figure E-11 shows that four N/S flight lines are needed to cover the same area.

Figure E-11 N/S Flight Lines

There are 6 neat models per flight line requiring 7 photos.

The total number number of photos needed is (4 lines) x (7 photos/line) = 28 photos

The N/S option requires 4 more photos. Although it looks like the northwestmost neat model could be eliminated, it only saves a single photo.

In either case, there is very little wiggle room. An additional flight line and possibbly one more neat model per line might be incorporated as a safety factor. Increasing the flying height increases neat model size, so that may be another alternative. It depends in part on the topography and desired accuracy of the final product.