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a plane that is perpendicular to the axis of a lens, mirror, or other optical system and at which rays diverging from a focal point are deviated parallel to the axis or at which rays parallel to the axis are deviated to converge to a focal point.
Based on the Random House Dictionary, © Random House, Inc. 2014.
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The height is measured from the floor to the
of the ceiling.
The shortest distance from a clear pixel to a cloud in the
is defined as cloud-free distance for the clear pixel.
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