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Contents

1. Training strategy
2. Maps
3. Marginal information and symbols
4. Grids
5. Scale and distance
6. Direction
7. Overlays
8. Aerial photographs
  - Comparison with maps
  - Types
  - Types of film
  - Numbering and titling information
  - Scale determination
  - Indexing
  - Orienting of photograph
  - Point designation grid
  - Identification of photograph features
  - Stereovision
9. Navigation equipment and methods
10. Elevation and relief
11. Terrain association
12. Mounted land navigation
13. Navigation in different types of terrain
14. Unit sustainment

A. Field sketching
B. Map folding techniques
C. Units of measure and conversion factors
D. Joint operations graphics
E. Exportable training material
F. Orienteering
G. M2 compass
H. Additional aids
I. Foreign maps
J. Global positioning system
K. Precision lightweight global positioning system receiver

Survival Gear

Handheld GPS
Specialty Outdoor Gear
Digital Compasses
Survival Books
Hunting and Fishing Magazines

8-5. SCALE DETERMINATION

Before a photograph can be used as a map supplement or substitute, it is necessary to know its scale. On a map, the scale is printed as a representative fraction that expresses the ratio of map distance to ground distance, For example:

RF = MD
——
GD

On a photograph, the scale is also expressed as a ratio, but is the ratio of the photo distance (PD) to ground distance. For example:

RF = PD
——
GD

The approximate scale or average scale (RF) of a vertical aerial photograph is determined by either of two methods; the comparison method or the focal length-flight altitude method.

a.   Comparison Method. The scale of a vertical aerial photograph is determined by comparing the measured distance between two points on the photograph with the measured ground distance between the same two points.

SCALE (RF = Photo Distance
————————
Ground Distance

The ground distance is determined by actual measurement on the ground or by the use of the scale on a map of the same area. The points selected on the photograph must be identifiable on the ground or map of the same area and should be spaced in such a manner that a line connecting them will pass through or nearly through the center of the photograph (Figure 8-8).

Figure 8-8. Selection of points for scale determination.

Figure 8-8. Selection of points for scale determination.

b.   Focal Length-Flight Altitude Method. When the marginal information of a photograph includes the focal length and the flight altitude, the scale of the photo is determined using the following formula (Figure 8-9).

Figure 8-9. Computation of scale from terrain level.

Figure 8-9. Computation of scale from terrain level.

When the ground elevation is at sea level, H becomes zero, and the formula is as shown in Figure 8-10.

Figure 8-10. Basic computation of scale from sea level.

Figure 8-10. Basic computation of scale from sea level.



Aerial photographs
Comparison with maps | Types | Types of film | Numbering and titling information | Scale determination | Indexing | Orienting of photograph | Point designation grid | Identification of photograph features | Stereovision |




Buy The Book This Site Is Based On
The 'Land Navigation' section of this site is based on 'Map Reading and Land Navigation', a public domain work published by the U.S. Department of Defense that is available for sale at Amazon.com.




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