mapref.orgon

8. October 1998
Notes
• Geographic co-ordinates are not planar coordinates!
• Geographic co-ordinates are based on a specific reference system (e.g. sphere or ellipsoid).
• Geographic co-ordinates define the perpendicular direction on the surface of the reference system.
• Geographic co-ordinates are ambiguous!
• Geographic co-ordinates may define different points on the earth's surface. This depends on their reference system (the geodetic datum problem).
• One point on the earth's surface may have many geographic co- ordinates, depending on their reference system (geodetic datum).
• Changing geographic co- ordinates means:
• Map Projection
Conversion from the curved surface to a plane.
• Geodetic Datum Transformation
Changing geographic co- ordinates between different reference systems or reference surfaces.
Terminology confusion with geographic coordinates
3 types of co-ordinates define different perpendiculars:
• astronomical coordinates
physically: perpendicular, based on the gravity
• geodetic coordinates
mathematically: perpendicular, based on the reference surface, specifically ellipsoid, used for large and medium scale mapping, and in geodesy.
• geographic coordinates
mathematically: perpendicular, based on the reference surface, typically spheres, used for small scale mapping
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