- GPS surveying shall establish photo-control points to check the new aerial photography. The location of the photo-control shall be strategically placed throughout the County in order to maintain the desired positional accuracy. The origin of the photo-control survey; the Network - GPS field surveys for the supplemental photo-control will originate from First-order NGS and/or CALTRANS control stations. NGS control station monuments are used as a primary source of horizontal survey control. These primary control monuments are used to locate other surveys.
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