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Short Citation:
National Geodetic Survey, 2023: Calibration Base Lines for Electronic Distance Measuring Instruments (EDMI),

Item Identification

Title: Calibration Base Lines for Electronic Distance Measuring Instruments (EDMI)
Short Name: cbl
Status: Completed
Publication Date: 1974

A calibration base line (CBL) is a precisely measured, straight-line course of approximately 1,400 m used to calibrate Electronic Distance Measuring Instruments (EDMI). A CBL usually consists of four segments ranging from 150 to 1,400 m whose lengths are measured with two high precision EDMI. Since the program began in 1974, NGS has established more than 300 base lines throughout the United States in cooperation with government agencies, universities and professional groups. Participating organizations must select a suitable site that is accessible for public use and install the base line markers 2 to 3 months before measurements are taken. Published CBL distances are available from the National Geodetic Survey, 301-713-3242 or For more information, please refer to: [1] NOAA Technical Memorandum NOS NGS-8 - Establishment of Calibration Base Lines (1994). [2] NOAA Technical Memorandum NOS NGS-10 - Use of Calibration Base Lines (1977). Both publications are available in pdf from


CBL's provide surveyors with a means to detect and correct errors in Electronic Distance Measuring Instruments (EDMI). These highly accurate base lines provide a locally accessible standard for length measurement.In addition, NGS makes available the PC program CALIBRAT. This program is used to determine the scale and constant corrections for electronic distance measuring instruments by utilizing measurements taken 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."



Supplemental Information:

Both mark-to-mark and horizontal distances are published. When the suggested grade specifications are met, it is a simple matter to place the instruments or reflectors at about the same height above the monuments. A direct comparison with the published mark-to-mark data can then be made. Unless steps are taken to set the instruments or reflectors such that the measured distances are in the horizontal plane between monuments, computations are required to compare the observed distances with the published horizontal values.


Theme Keywords

Thesaurus Keyword
ISO 19115 Topic Category
ISO 19115 Topic Category
NOS Data Explorer Topic Category Geodetic/Global Positioning
None Calibrations
None Distances
None Geodetic/Global Positioning
None oceans
None Topographic Data

Spatial Keywords

Thesaurus Keyword
None U.S. Exclusive Economic Zone
None United States

Physical Location

Organization: National Geodetic Survey
City: Silver Spring
State/Province: MD

Data Set Information

Data Set Scope Code: Data Set
Maintenance Frequency: As Needed
Data Presentation Form: document
Distribution Liability:


Support Roles

Data Steward

CC ID: 489638
Date Effective From: 1974
Date Effective To:
Contact (Organization): NGS Communications and Outreach Branch
Email Address:
Phone: (301) 713-3242
Fax: (301) 713-4172


CC ID: 489640
Date Effective From: 1974
Date Effective To:
Contact (Organization): NGS Communications and Outreach Branch
Email Address:
Phone: (301) 713-3242
Fax: (301) 713-4172

Metadata Contact

CC ID: 489641
Date Effective From: 1974
Date Effective To:
Contact (Organization): NGS Communications and Outreach Branch
Email Address:
Phone: (301) 713-3242
Fax: (301) 713-4172

Point of Contact

CC ID: 489639
Date Effective From: 1974
Date Effective To:
Contact (Organization): NGS Communications and Outreach Branch
Email Address:
Phone: (301) 713-3242
Fax: (301) 713-4172


Currentness Reference: Publication Date

Extent Group 1

Extent Group 1 / Geographic Area 1

CC ID: 489644
W° Bound: -175
E° Bound: -67
N° Bound: 71
S° Bound: 18

Extent Group 1 / Time Frame 1

CC ID: 489643
Time Frame Type: Continuing
Start: 1974

Access Information

Security Class: Unclassified
Data Access Constraints:


Data Use Constraints:


Distribution Information

Distribution 1

CC ID: 489645
Download URL:

Downloadable Data

File Type: ASCII Text



CC ID: 489637
URL Type:
Online Resource

Activity Log

Activity Log 1

CC ID: 489658
Activity Date/Time: 2012-12-11

Date that the source FGDC record was last modified.

Activity Log 2

CC ID: 489657
Activity Date/Time: 2017-04-05

Converted from FGDC Content Standards for Digital Geospatial Metadata (version FGDC-STD-001-1998) using '' script. Contact Tyler Christensen (NOS) for details.

Activity Log 3

CC ID: 717053
Activity Date/Time: 2018-02-08

Partial upload of Positional Accuracy fields only.

Data Quality


The accuracy of each distance segment is determined through a least squares adjustment procedure on the assumption the data points were established in a straight line. Accuracies are on the order of 0.1 to 0.3 mm per line segment. Actual accuracies are stated on each individual CBL document.

Horizontal Positional Accuracy:

The coordinates for each CBL are generally scaled from a topo map or positioned using a GPS unit.

Vertical Positional Accuracy:

The published elevations are for distance reduction purposes only. They are not tied to the the National Vertical Datum. The relative differences between elevations are better than +/-12 mm.

Completeness Report:


Conceptual Consistency:



Process Steps

Process Step 1

CC ID: 489635

Calibration Base Line monuments are set on a straight line by the requesting organization. After a sufficient time to allow for settling, the base line is measured with two high accuracy short range EDMI on 2 separate days. Observations will be made such that all segments are measured, forward and backward, on each of the 2 days with both instruments. For a 4 monument base line, this will provide a total of 12 distinct observations with each instrument per day. A total of 48 observations during the 2 days will have been taken. Observations are field checked prior to submittal to NGS for adjustment. NGS will check the EDMI before and after each project to insure the observations meet length standards set by the National Bureau of Standards. All observations are then adjusted through a least squares adjustment procedure and thoroughly checked prior to publication.Process Date Range is 1974-present

Catalog Details

Catalog Item ID: 39910
GUID: gov.noaa.nmfs.inport:39910
Metadata Record Created By: Tyler Christensen
Metadata Record Created: 2017-04-05 13:07+0000
Metadata Record Last Modified By: SysAdmin InPortAdmin
Metadata Record Last Modified: 2023-05-30 18:09+0000
Metadata Record Published: 2018-02-08
Owner Org: NGS
Metadata Publication Status: Published Externally
Do Not Publish?: N
Metadata Last Review Date: 2018-02-08
Metadata Review Frequency: 1 Year
Metadata Next Review Date: 2019-02-08