4. Parallax Equations

a. Ground Coordinates

The ground coordinate system is similar to that of a single vertical photo. The origin and axes directions are defined by the left photo, Figure F-10, using the actual flight direction.

Figure F-10
Ground Coordinate System


Coordinates and elevation of ground points can be determined from parallax measurements using equations F-4 through F-6.

Equation F-4 
Equation F-5 

Equation F-6 

b. Elevations by Parallax

Figure F-11 shows the basic parallax and elevation geometry for two points.

Figure F-11
Parallax and Elevation Difference 


If we can measure the parallax of both points, we can determine one point's elevation based on the other, Equation F-7.


Equation F-7