This attribute indicates how to interpret the edges of the geometries: whether the line between two points is a straight cartesian line or the shortest line on the sphere (geodesic line). Available values are:
"planar": use a flat cartesian coordinate system.
"spherical": use a spherical coordinate system and radius derived from the spheroid defined by the coordinate reference system.
If no value is set, the default value to assume is "planar".
Does this literally mean that the path between two points is the geodesic path on the sphere (= great circle route) even though the datum is (very likely to be) an ellipsoid (= spheroid)?
A) If true, then this is a strange definition for a path, given that it has no particular meaning on a spheroid. It is also ambiguous because the derivation of the radius is not specified (authalic sphere? conformal sphere? rectifying sphere? something else…?).
B) If the meaning is actually the geodesic path on the spheroid, then the geometric treatment of this path would be extremely painful due to the mathematical complexity.
Because of (B), some data formats, such as SQL Server, use the great elliptic arc, which is close to the geodesic.
Does this literally mean that the path between two points is the geodesic path on the sphere (= great circle route) even though the datum is (very likely to be) an ellipsoid (= spheroid)?
A) If true, then this is a strange definition for a path, given that it has no particular meaning on a spheroid. It is also ambiguous because the derivation of the radius is not specified (authalic sphere? conformal sphere? rectifying sphere? something else…?). B) If the meaning is actually the geodesic path on the spheroid, then the geometric treatment of this path would be extremely painful due to the mathematical complexity.
Because of (B), some data formats, such as SQL Server, use the great elliptic arc, which is close to the geodesic.