ABSTRACT
When working with spatial data, the simplest model is a one-dimensional distance. Models of increasing complexity include a two dimension (2-D) plane coordinate system formed by the perpendicular intersection of the X and Y axes, a generic three dimension (3-D) X/Y/Z rectangular Cartesian coordinate system having three mutually perpendicular axes, a spherical Earth model, and finally, the ellipsoidal Earth model. Expanding attention from the local 2-D and 3-D considerations, traditional spatial data models include a variety of 2-D and 3-D options. Although the equations used in the Global Spatial Data Model (GSDM) are included as a part of the traditional 3-D models, the GSDM is different in that the arrangement of equations and the computations are based on the assumption of a single origin for 3-D spatial data. A computational example comparing three different models— geodetic, cartographic, and 3-D— for the same simple 3-D position computation is contained in an article by E. F. Burkholder.
