3-D COGO and
Based on the GSDM
Global COGO, Inc.
Las Cruces, NM 88003
Earl F. Burkholder, PS, PE, F.ASCE
Home Page: See "Documents" page for information on 3-D book!
This web site promotes use of the 3-D Global Spatial Data Model (GSDM) which can be
used for computations based on either spatial data or geospatial data.
1. Spatial data (e/n/u) are characterized by parallel plum lines at all points (flat-Earth).
2. Geospatial data are those referenced to the Earth. Commonly used coordinate systems are:
a. Geodetic latitude/longitude/height.
b. Geocentric Earth-fixed Earth-centered (ECEF) rectangular X/Y/Z coordinates.
(Local coordinate differences, de/dn/du, are computed from ECEF differences.)
c. State plane (map projection) coordinates and elevation.
(Map projections (2-D) and elevations (1-D) have different origins.)
The GSDM uses a 3-D model for 3-D data and preserves geometrical integrity whether using spatial
data or geospatial data. (The difference is due to gravity.) The GSDM provides the following benefits:
1. Geoid modeling is rarely needed if geodetic (ellipsoid) height is used for the third dimension.
2. Unlike LDP projections, the GSDM gives the local horizontal distance without distortion.
3. Local direction and distance to any point (in a cloud) are available from any user perspective.
4. The GSDM includes procedures for establishing and tracking spatial data accuracy.
Diagram of 3-D coordinate system relationships click here.
Graphical visualization of coordinate systems click here.
Overview of Datum Replacement Challenges, 2016 AGU Poster.
Previous versions of this web site are archived. November 2021
This web page first posted October 31, 2021, and last updated 11/24/2021.
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BURKORD® is a trademark of Global COGO, Inc.