This short statement is a summary of the global spatial data model
(GSDM). A defining copyrighted 30 page document,
Definition and Description of a Global Spatial Data Model, is available
over the web or from the author, Earl F. Burkholder
Spatial data are three-dimensional (3-D). Modern measurement systems collect data in a 3-D spatial environment. Some data are used as one- dimensional (elevations and linear referencing), some are used as two- dimensional (maps, and construction drawings) and some are used as three- dimensional (digital terrain models and other data visualization applications). A 1-D data base will not support 2-D or 3-D applications. Neither will a 2-D data base support 3-D applications. A 3-D data base will support all three.
An arrangement of existing mathematical equations and procedures define and describe a Global Spatial Data Model (GSDM) which is based upon rules of solid geometry and the earth-centered earth-fixed (ECEF) geocentric coordinate system. The GSDM includes both functional model (geometrical relationships) and stochastic model (standard deviation and error propagation) components. Including no new science, the GSDM is an arrangement of existing concepts and offers numerous advantages to many spatial data users world-wide. A key feature of the GSDM is use of local coordinate differences which preserves the local perspective at all times. For example, an inverse between points gives the local horizontal tangent plane distance, not a state plane grid distance or distance on the ellipsoid. Azimuths are also accurately portrayed.
The GSDM accommodates modern measurements whether GPS, survey total station, or photogrammetric mapping. Digital spatial data are stored as X/Y/Z ECEF coordinates and the quality of position is given by the variance/covariance data for each point. All other expressions (latitude/longitude, state plane, and UTM) are derived from the X/Y/Z values. The standard deviations of all components (north/east/up) are derived and printed upon demand. The standard deviation of any other derived quantity (distance and/or azimuth) is also immediately available from information stored in the GSDM.
The GSDM also supports elevations at the same level of accuracy as available geoid height information. Given completion of GEOID96 by the National Geodetic Survey (NGS), the elevation of points within the United States can be obtained at a level of accuracy approaching, if not exceeding, that obtained with traditional leveling - especially if used in the relative mode.
There are many issues related to implementation of the GSDM. At the simplest level, anyone can start with the 3-D X/Y/Z positions of existing HARN stations and build their own network. The HARN positions can be assumed errorless or reasonable assumptions can be made about the quality of published coordinates. The positional accuracy of newly established points is based upon the accuracy of the control points used and the variance/covariance data for the GPS base line vectors, the standard deviations of the total station observations or error propagation during the photogrammetric mapping process.
On the other hand, implementation of the GSDM on a global scale includes issues such as satellite orbits, earth tides, earthquakes, subsidence, continental drift, reference frames, and other issues. Even so, the GSDM can be used as a unifying environment in which scientific and other issues are examined and evaluated under a common well-defined set of solid geometry spatial data relationships.
Prototype DOS-based menu-driven software which performs 3-D coordinate geometry
and related error propagation computations is called
BURKORD®.
Read a better mouse trap description of the GSDM.
Read the anecdotal pan story about using an appropriate 3-D model.
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