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Term |
Definition/Description |
Source |

z-axis |
In a three-dimensional rectangular coordinate system, the axis of reference that is perpendicular to both the x- and y-axes at their point of intersection. | HDBK-850 |

zenith |
That point of the celestial sphere vertically overhead. See also geocentric zenith; geodetic zenith. |
HDBK-850 |

zenith angle |
See zenith distance. |
HDBK-850 |

zenith camera |
A special camera so designed that its optical axis may be pointed accurately toward the zenith. It is used for the determination of astronomic positions by photographing the position of the stars. See also photographic zenith tube. |
HDBK-850 |

zenith distance |
The vertical angle between the zenith and the object which is observed or defined. Zenith distance is the complement of the altitude. Also called zenith angle. See also coaltitude. |
HDBK-850 |

zenith telescope |
A portable instrument adapted for the measurement of small differences of zenith distance, and used in the determination of astronomic latitude. | HDBK-850 |

zenithal chart |
See azimuthal chart. |
HDBK-850 |

zenithal map projection |
See azimuthal map projection. |
HDBK-850 |

zero meridian plane; zero meridian |
The chosen meridian plane from which longitude is measured. The zero meridian plane is actually only a half-plane, on one side of the polar axis. Often abbreviated to zero meridian although strictly speaking a meridian is a line of intersection of the plane along a reference surface, for example an ellipsoid. | CEN/TC 287 |

z-motion |
Movement of a stereoplotting projector in a vertical direction. | HDBK-850 |

zonal harmonics |
The set of spherical harmonics that are functions of latitude only and therefore do not affect the rotational symmetry of the surface about its polar axis. |
HDBK-850 |

zone time |
The local mean time of a reference zone. See also time zone. |
HDBK-850 |

zoom system |
See pancratic system. |
HDBK-850 |

z-scale |
(JCS) On an oblique photograph, the scale used in calculating the height of an object. Also, the name given to this method of height determination. |
HDBK-850 |

ZULU time |
See Universal Time (UT1). |
JPUB 1-02 |

z-value data points |
Data points providing a value perpendicular or normal to a specified surface (elevation). | HDBK-850 |

*Last Updated by Mark Owens 17 February 1999.*