Survey marker

Survey markers, or survey monuments, are objects placed to mark key survey points on the earth's surface. They are used in geodetic and land surveying. Vertical elevation markers are also known as benchmarks, and horizontal position markers used for triangulation are also known as trig points. Survey markers may be of one or both types. [ [http://www.unm.edu/~creelbm/pages/benchmark/benchmarks_explain.html Photos of Witness Posts and Survey Marks ] ]

Survey markers are placed for use during a survey, and for possible use in subsequent surveys. They are usually durable and intended to be permanent. Markers may be as simple as a chisel mark or nail, or they may be cast and stamped metal disks set in rock or concrete pillars. Trig points may also incorporate an instrument mount for use with a theodolite.

Important geodetic survey markers were often placed in groups, and also stacked vertically underground, to allow the original mark to be recovered if it was disturbed. Current best practice for stability of new survey markers is to use a punch mark stamped in the top of a metal rod driven deep into the ground, surrounded by a grease filled sleeve, and covered with a hinged cap set in concrete. [ftp://ftp.ngs.noaa.gov/pub/uddf/info/Attach_10.pdf]

Survey markers are now often used to set up a GPS receiver antenna in a known position for use as a reference point in Differential GPS surveying.

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