Triangulation stations were often occupied by erecting towers equipped with lights that could be seen from a distance at night. The triangulation measurements were then based on observation of the light. The height of the light above the station mark was measured because it could be factored into the calculation of the position of the station, for instance in corrections for refraction due to temperature gradients near the ground, or adjustments to project the computed distance onto the geoid.

height of light (last edited 2009-03-21 21:03:18 by localhost)