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User Comments
  Posted by Mircea LUTIC on May 25, 2005
The result of GLength() depends on the type of Spatial Reference (SRID).

The value above is based on euclidian geometry.
The length of a line (and hence of a LineString and MultiLineString) is given by
SQRT ( (x2-x1)^2 + (y2-y1)^2 )
only in planar (euclidian) geometry.

If x & y are spherical lattitude and longitude then the distance between 2 points of coordinates (lng1,lat1) and (lng2,lat2) is given by
distInRadians = acos ( sin(lat1)*sin(lat2) +cos(lat1)*cos(lat2)*cos(lng2-lng1) )
distInMeters = distInRadians * RadiusOfSphere

See also My comment on MultiPolygon Functions
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