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Know the Earth…Show the Way

NATIONAL GEOSPATIAL-INTELLIGENCE AGENCYApproved for public release #05-328.

LEADSLEADSThe Essential Elements of a 3-D Geographic CoordinateThe Essential Elements of a 3-D Geographic Coordinate

John W. Dix13 September 2005ESRI Homeland Security GIS Summit - Denver, [email protected]

John W. Dix13 September 2005ESRI Homeland Security GIS Summit - Denver, [email protected]

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NATIONAL GEOSPATIAL-INTELLIGENCE AGENCY

Know the Earth…Show the WayApproved for public release #05-328.

LEADSOverview

LEADS is a framework for reporting the LEADS is a framework for reporting the essential elements of a three dimensional essential elements of a three dimensional (3(3--D) geographic coordinateD) geographic coordinate

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LEADSBackground

• Global Positioning System (GPS) provides a worldwide network for determining precise geodetic positions

• GPS geographic coordinates based on the WGS-84 ellipsoid are global, standardized, precise, and reliable

• GIS provide geographic coordinates in a variety of formats which may not be referenced to a datum and lack information about source and accuracy of a coordinate

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LEADSComparison of GPS and GIS

LEADSComparison of GPS and GIS

GPS GIS

• Geocentric• Absolute Positioning• Coherent Network• Precise• WGS-84 Datum• Worldwide

• Image Space• Object Characterization• Various Implementations• Inconsistent Accuracy• Various Datums• Worldwide

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LEADSThe 5 Elements of LEADS

• L: Latitude and Longitude• E: Elevation • A: Accuracy• D: Datum• S: Source

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LEADSHeight Above Ellipsoid

&Mean Sea Level

Surface of Earth

Mean Sea Level

WGS-84Ellipsoid

Elev

atio

nA

bove

Mea

n Se

a Le

vel

HeightAbove Ellipsoid

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LEADSThe 5 Elements of LEADS

• L: Latitude and Longitude• E: Elevation

• Height Above Ellipsoid (GPS)• Mean Sea Level (MSL)

• A: Accuracy• Horizontal• Vertical

• D: Datum• WGS-84 Ellipsoid• North American Datum 1983• Other

• S: Source• GPS Receiver• Paper map or chart series• Geographic Information System• Other

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LEADSValue Added

• Provides producers and users a common framework for transferring and assessing geographic coordinates from different sources

• Allows users to correlate geographic coordinates from various sources, such as GIS, paper maps and charts, and GPS receivers

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LEADSProcess

StandardizedProduction

Process

SystemDesign

&Development

LEADS

• Standards Based> Systems

Engineering> Application

Interfaces

Procedures&

Training

ProcessedGeographicCoordinates

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LEADSSummary

• LEADS defines the minimum set of data elements required to accurately characterize a geodetic coordinate

• LEADS does not satisfy every need, but is a simplified format for describing the most important elements of a geographic coordinate

• LEADS concept can be broadly applied in military, scientific, and technical applications

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LEADS Recommendations

• Know the heritage of the coordinate(s) you are using• Build quality into the process instead of inspecting for

quality after production (W. E. Deming)• Define community best practices for determining,

communicating, integrating, and displaying geographic coordinates

• Develop Graphical User Interfaces, applications, mensuration software, and Application Program Interfaces (API) that implement best practices

• Use display format for geographic coordinates that is readily understood– Degrees/Minutes/Seconds (D/M/S) versus Decimal

degrees (D.dddddd)• Adopt best practices in software and system engineering

that display geographic coordinate at a level of precision consistent with the accuracy of the source from which the coordinate is derived

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LEADS Conclusion

Geospatial information community would benefit from a standard methodology for correlating geographic coordinates from GIS, imagery, and paper maps and charts with geographic coordinates from GPS receivers.

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LEADSTechnical Details Worth Remembering

• Image resolution is not an indicator of geopositional accuracy– One meter pixels do not mean one meter

geopositional accuracy• Adding decimal precision to an inaccurate

coordinate does not make it more precise and dilutes its integrity

• Measuring a coordinate to nearest 0.001 seconds of arc (1.2 inches), is rarely possible, leaves the impression that a coordinate is precise, and complicates correlating coordinates from multiple sources

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LEADSTechnical Details Worth Remembering

At the equator:

• One minute of arc equals one nautical mile (~6080 feet)

• One second of arc equals approximately 101 feet:– 0.01 arc seconds = 1 foot– 0.001 arc seconds = 0.1 feet (1.2 inches)

• One degree is approximately 364,800 feet:– 10-5 degrees ~ 3.6 feet– 10-6 degrees ~ 4 inches– 10-7 degrees ~ 1/2 inch

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Know the Earth…Show the Way

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