What is the difference between plane and geodetic datum reference systems?
A plane reference system uses a flat surface as the origin or 0 elevation. A flat surface does not account for the curvature of the earths surface and should not be used for large projects. Typically these small surveys may not even be referenced to the NSRS and might use a local mark with an assumed elevation (i.e. 100.0) which would be considered a local datum. Geodetic datums define the size and shape of the earth and the origin and orientation of the coordinate systems used to map the earth. Hundreds of different datums have been used to frame position descriptions since the first estimates of the earth’s size were made by Aristotle. Datums have evolved from those describing a spherical earth to ellipsoidal models derived from years of satellite measurements. Back to top 3. What is the geoid? What is the ellipsoid? Why do we need both reference systems. The geoid is an equipotential gravitational surface that is approximated by mean sea level and is everywhere perpendicular to the
