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Re: 3-D coordinates on a sphere
Posted by: Peter Yuill
Date: November 11, 2005 12:31AM

The stated basis of the spatial extension is the OpenGIS Simple Features Spec for SQL. This is a 2D feature model, but you are free to choose your own coordinate system for those two dimensions. An earth based CS with two dimensions (lon and lat) models the general shape of the earth pretty well, just not the height above the ellipsoid. For many purposes this provides acceptable accuracy, and I suspect yours is one of them.

The snag of course is that the calculation of distance between two points on the earth (the orthodromic distance) needs to be made by geospatial software that is definitely not in the MySQL engine, and I suspect never will be. However there is a wealth of open source software available today to do that. The excellent Geotools library http://www.geotools.org/ is a great place to start. The org.geotools.referencing.datum.DefaultEllipsoid class has an orthodromicDistance() method.

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