true horizon


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Related to true horizon: horizon line

true horizon

1. The boundary of a horizontal plane passing through a point of vision.
2. In photogrammetry, the boundary of a horizontal plane passing through the perspective center of a lens system.
References in periodicals archive ?
That's the distance to the true horizon on Earth in miles--to a remarkable accuracy of nearly 1 part in 1,000.
This is especially critical at night with a low cloud layer and an absence of a true horizon.
At Sun angle -13[degrees] below true horizon, dawn flats can be taken prior to parking the 'scope and closing the roof.