Horizontal Datum
Defines relationship between the ellipsoid adopted as the model of the Earth’s shape, and the Earth itself
- A localization of a specified ellipsoid
- SEDRIS defines 181 standard datums, their reference ellipsoid, and applicable extents
- All use Greenwich as their Prime Meridian
- Almost all are local in scope
WGS-84 datum is global in scope
- Common “master” datum for interconversions
- SEDRIS supports Molodensky Method (3 parameter)
- May need to also support higher accuracy method