COORDINATE SYSTEMS

COORDINATE SYSTEMS•An overview of coordinate systems for georeferencingprovides a brief description of local and global systems for usein precise positioning, navigation, and geographic informationsystems for the location of points in space.•There are many different coordinate systems, based on avariety of geodetic datums, units, projections, and referencesystems in use today.

Coordinate System• There are many different coordinate systems, based ona variety of geodetic datums, projections, , and unitsin use• Geographic coordinate systems (no projection):Spheroid (or Ellipsoid)-based systems, local systems.• Projected coordinate systems: world, continental, polar,US National Grids, UTM, state plane.open ArcGIS for a demo

Geographic Latitude/LongitudeCoordinate System

•Plane Coordinate Systems•Two-dimensional coordinate systems are defined with respect toa single plane.

Coordinate SystemsGlobal Systems•Latitude, Longitude, Height•The most commonly used coordinate system today is thelatitude, longitude, and height system.•The Prime Meridian and the Equator are the referenceplanes used to define latitude and longitude.• Equator and Prime Meridian

Geodetic Latitude, Longitude, and Height•The geodetic latitude (there aremany other defined latitudes) of apoint is the angle from the equatorialplane to the vertical direction of aline normal to the referenceellipsoid.•The geodetic longitude of a point isthe angle between a reference planeand a plane passing through thepoint, both planes beingperpendicular to the equatorial plane.•The geodetic height at a point is thedistance from the reference ellipsoidto the point in a direction normal tothe ellipsoid.

•ECEF X, Y, Z•Earth Centered,Earth Fixed Cartesiancoordinates are alsoused to define threedimensionalpositions.•Earth centered,earth-fixed, X, Y, andZ, Cartesiancoordinates (XYZ)define threedimensional positionswith respect to thecenter of mass of thereference ellipsoid.

Geographic Latitude/Longitudeon a flat surface (WGS 84 datum)Scale,distance, area,and shape areall distortedwith thedistortionincreasingtoward thepoles.

Geographic Latitude/Longitudein GIS system90º West EastNorth-180 ºequator0 ºPrime Meridian0 º180 ºSouth-90 ºopen ArcGIS for a demo

Universal Transverse Mercator(UTM) Coordinate System• UTM system is transverse-secant secant cylindrical projection, dividing the surface of theEarth into 6 degree zones with a central meridian in the center of the zone. each oneof zones is a different Transverse Mercator projection that is slightly rotated to use adifferent meridian. UTM zone numbers designate 6 degree longitudinal stripsextending from 80 degrees South latitude to 84 degrees North latitude. UTM is aconformal projection, so small features appear with the correct shape and scale isthe same in all directions. (all distances, directions, shapes, and areas are reasonablyaccurate ). Scale factor is 0.9996 at the central meridian and at most 1.0004 at theedges of the zones.• UTM coordinates are in meters, making it easy to make accurate calculations of shortdistances between points (error is less than 0.04%)• Used in USGS topographic map, and digital elevation models (DEMs)• Although the distortions of the UTM system are small, they are too great for someaccurate surveying. zone boundaries are also a problem in many applications,because they follow arbitrary lines of longitude rather than boundaries betweenjurisdictions.

UTM Zone Numbers

Transverse-secant secant Cylindrical(Mercator) ProjectionMost New Mexico in Zone 13CM: central meridianAB: standard meridianDE: standard meridian-108-105-102

false easting~0 mE ~1,000,000 mEequator 0 mN or10,000,000 mSfalse northing

Universal Polar Stereographic(UPS) Coordinate System• The UPS is defined above 84 degrees north latitudeand south of 80 degrees south latitude.• The eastings and northings are computed using apolar aspect stereographic projection.• Zones are computed using a different character setfor south and north Polar regions.