Measuring Distance on the Earth


The words "geodesic" and "geodetic" are used in the following ways in geography.

  1. When talking about coordinates, "geodetic longitude" and "geodetic latitude" are just fancy ways to say longitude and latitude. Hence, "geodetic coordinates" means the same thing as "geographic coordinates."
  2. When talking about distance on the earth, "geodetic distance" and "geodesic distance" are the same thing: the shortest path along the ellipsoid of the earth at sea level between one point and another.

The OpenGIS Consortium refers to several kinds of distance.  The following is extracted from their abstract specification:

"The role of the reference system in distance calculations is important. Generally, there are at least three types of distances that may be defined between points (and therefore between geometric objects): map distance, geodetic distance, and terrain distance.

Calculation of the Geodesic