Application Risks to Operations and Adherence to DoD World Geodetic System 1984 (WGS 84)
This message outlines the risks associated with the use of Web Mercator applications for DoD and GEOINT user community operations. The NGA Geomatics Office has assessed the use of Web Mercator and other non-WGS 84 spatial reference systems may cause geo-location / geo-coordinate errors up to 40,000 meters. This erroneous geospatial positioning information poses an unacceptable risk to global safety of navigation activities, and department of defense, intelligence community, and allied partner systems, missions, and operations that require accurate and precise positioning and navigation information. The NGA Geomatics Office reminds the community to use DoD approved World Geodetic System 1984 (WGS 84) applications for all mission critical activities.
Many popular commercial visualization, mapping and mobile web device applications use a Web Mercator spherical earth reference. These applications are not an equal alternative to DoD WGS 84, as they do not provide the same geo-coordinates or geo-location accuracies. Common terms associated with non-WGS 84 applications include but are not limited to: Web Mercator, WGS 84 Web Mercator, WGS 1984 Web Mercator (auxiliary sphere) and European Petroleum Survey Group (EPSG) Spatial Reference System Identifier (SRID) (such as) EPSG: 3857. Users are advised that many projected, un-projected, and local spatial coordinate system definitions do not conform to WGS 84.
A spherical or Web Mercator spatial reference system uses mathematical formulas and parameters that are incompatible with and non-compliant to the WGS 84. Noted defects extend to erroneous calculation of ground control points, positional system data, and variance with WGS 84 GEOINT (imagery, geospatial information, and imagery intelligence).
Authority: in accordance with Chairman of the Joint Chiefs of Staff Instruction, (CJCSI 3900.01C), 30 June 2007, Position (Point and Area) Reference Procedures, WGS 84 is directed for standardization by the National System for Geospatial-Intelligence (NSG), Allied System for Geospatial Intelligence (ASG), North Atlantic Treaty members, and Intelligence Community (IC) members, to fully support geographic coordinate accuracy and interoperability requirements.
Recommended course of action: in accordance with CJCSI 3900.01C, users and associated programs will continue to reference coordinates (horizontal and vertical) to DoD approved WGS 84 spatial reference system. Additional references on the Web Mercator issue and the use of WGS 84 are available at the following URLs:
· JWICS: http://www.geoint.nga.ic.gov/products/gandg/
· SIPRNET: http://www.geoint.nga.smil.mil/products/gandg/
· NIPRNet: http://osis.nga.mil/GandG/index.htm
· Internet: http://earth-info.nga.mil/GandG/
For assistance please contact the NGA Geomatics Office (SN) using the point of contact information provided below:
· NGA Geomatics Office
· Phone: (314) 676-9123, DSN: 846-9123
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