8.
October 1998Notes
- 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 Coordinates
means:
- Map
Projection
Transformation from the curved surface to a plane.
- Geodetic
Datum Transformation
Changing geographic coordinates between different reference systems or reference
surfaces.
Terminology confusion
with geographic coordinates
3 types of co-ordinates define differentperpendiculars:
- astronomical
coordinates
physically defined perpendicular, based on the gravity
- geodetic
coordinates
mathematically defined perpendicular, based on the reference surface, specifically ellipsoid
, used
for large and medium scale mapping, and in geodesy.
- geographic
coordinates
mathematically defined perpendicular, based on the reference surface, typically spheres,
used for
small scale mapping
related information
