Datums and Coordinates

Datums &

Coordinate Systems

Objective

• Identify different datums

• Identify different coordinate systems

Coordinate Systems

• Latitude and Longitude

• Universal Transverse Mercator (UTM)

Lat / Long Coordinate System

Latitude

Parallels of latitude

0° latitude

northlatitude

southlatitude

90°N

equator

Lat / Long Coordinate System

Longitude

West Longitude

Meridians of longitude0° longitudePrime Meridian

Eastlongitude

Grenwich, England

UTM Coordinate Systems

Allows projection of a spherical surface onto a flat surface

A plane coordinate system to relate the coordinates of points on earth’s curved surface with the coordinates of the same points on a plane or flat surface

UTM Zones in North America174180 168 162 156 150 144 138 132 126 120 114 108 102 96 90 78 72 54606684 48

“Figure” of the EarthBest-fit ellipsoid(e.g., GRS-80, WGS-84)

Datum and Ellipsoids

• Datum - represented by ellipsoid

• Reference ellipsoid examples: • Clarke 1866• GRS 80• WGS 84

Common Geographic Datums

• NAD27• NAD83• WGS84• ITRF00

NAD27: Clarke 1866 ellipsoidorigin in Kansas

Datum Origin

on Surface of

Earth

Ellipsoid Model based on less precise surveys

NAD27: Leaving Behind • Invented Space Travel

• Increasing accuracy of surveys

• Shift from optical surveys to a mathematical model of the Earths shape

• The result is a specific point on the landscape can take on multiple meanings

GPS Datum: WGS 84

Origin is at the Earth’s center of mass (geocentric)

This is the datum used for the NAVSTAR GPS satellites

WGS84:WGS84 ellipsoidorigin center of earth

The origins of the WGS84 and NAD83 ellipsoids are at the center of the earth’s mass, which makes them ideal for a GPS datum

Datum Adjustments• Known as Datum Adjustments or Epochs

• WGS84 (G1150) – most current version

• “Original” NAD83 = NAD83 (1986)– NAD83 (1992)– NAD83 (2002)– ……

• Most Current NAD83– NAD83 (CORS96) (Epoch 2003.00)

Differences between Datums

NAD27 ≠ NAD83 (1986)

33 to 700 feet

Differences between Datums• WGS84 = ITRF00

about 2cm

• NAD83 (CORS96) ≠ WGS84about 4.3 feet