Geodesy: The Mathematics of “Where”

Geodesy is the field of applied mathematics that studies Earth’s shape, orientation, positions and gravity for the past, present and future.

Ellipsoids, survey benchmarks and triangulation – these are the ingredients for geodetic datums. NAD27, NAD83 and WGS84 are common datums in North America.

NAD83 – We’re Not in Kansas Anymore

North American Datum of 1983 (NAD83) is 2-meters from geocentric and uses thousands of monuments with triangulation to create a reference frame for Earth

World Geodetic System (WGS84)

The World Geodetic System 1984 (WGS84) is the spatial reference system of GPS satellites with an error of less than 2 centimeters to the center of Earth.

Latitude, Longitude and Coordinate System Grids

Latitude lines run east-west, are parallel and go from -90 to +90. Longitude lines run north-south, converge at the poles and are from -180 to +180.

NAD27 and NAD83 may differ in tens of meters for horizontal accuracy on location. Datum transformations correct your data from one datum to another.

Ellipsoid/Spheroid – Our Oblate Spheroid Planet Earth

Reference ellipsoids (ex. Clarke Ellipsoid) are smooth, mathematical models of the Earth’s shape. It has a semi-major and minor axis flattened at the poles.

What is a Horizontal Datum Reference Frame?

A horizontal datum provides a reference frame for latitude and longitude coordinates on the Earth. A datum is constructed through surveys and triangulation.

NAD27 – Maede’s Ranch at the Center of It All

Maede’s Ranch was the focal point of the NAD27 with all positions relative to it. First-order triangulation was used with approximately 26,000 survey points