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### 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 |