NGS conducts a cooperative program that provides surveyors with a means to
detect and correct errors in Electronic Distances Measuring
Instruments (EDMI). NGS has established more than 300 EDMI Calibration
Base Lines (CBL) throughout the United States in cooperation with
various government agencies, universities, professional societies, and others.
These highly accurate base lines provide a locally accessible standard for
length measurement. For each state, NGS provides users with location
descriptions and the adjusted results of calibration base line measurements.
Calibration Base Line data
are available online. The file naming convention consists of a two letter
U.S. state code for current data. Files with an extension of .his
consist of CBL historic data.
PC software CALIBRAT is used
to determine the scale and constant corrections for electronic distance
measuring instruments by making measurements over previously determined
base lines. The formulas used in the program are found in NOAA Technical
Memorandum NOS NGS-10: Use of Calibration Base Lines.
NGS EDMI calibration base line policy.
NOAA Technical Memorandum NOS NGS-8: Establishment of Calibration Base
Lines, by Dracup, Fronczek, Tomlinson, and Spofford, 1994, 17 pp.
NOAA Technical Memorandum NOS NGS-10: Use of Calibration Base Lines, by
Fronczek, December 1977, reprinted 1980, 38 pp.