3-D COGO and Error Propagation Based on the GSDM

Global COGO, Inc. P.O.Box 3162 Las Cruces, NM 88003
 Earl F. Burkholder, PS, PE, F.ASCE
 Email: eburk@globalcogo.com 
 URL:   www.globalcogo.com 
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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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