Information on permanently monumented control points including horizontal control, vertical control, High Accuracy Reference Network (HARN) stations, Calibration Baselines and retrieval software can be obtained from the NGS web site or from the National Geodetic survey (NGS) Data Center on CD ROM. The Data Center may be reached at 301-713-3242. The cost of the CD is $50.00.
The map above shows the location of HARN points in Maryland. The position of these points was determined by GPS observations and have a stated accuracy of 1.0 to 0.1 parts per million.
The map above shows the approximate location of the six calibration baselines located in Maryland. A calibration baseline consists of a set of very stable survey monuments which are accurately measured using specialized equipment. By comparing their results with the values published for the monuments, surveyors are able to verify the accuracy of their equipment.
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