27.08.2011As already declared, a planar representation of the Earth has deformations compared
to its shape
on the Earth surface. These deformations depend on its position and the nature and specification of
the map projection instance.
One way to minimise the deformation properties is to use an appropriate mapping surface
like a
cylinder, cone or horizontal plane and its aspect (alignment) as well as its coincidence with the
Earth model. These characteristics are called the geometric extrinsics of the mapping
surface:
mapping surfaces:
their shape, aspects and coincidence [Voser 2003]The nature of the mapping surface:
- cylinder
- cone
- plane
- polysuperficiality
(a continuous system of mapping surfaces)
These mapping surfaces may be
aligned in different ways. The name of
its aspect is given based
on the orientation of the axis of the mapping surface with the axis of the Earth. In literature, also
other terms are used (see e.g. [Goussinsky 1951, Lee
1944, Richardus/Alder
1974, Snyder
1987]).
- normal
or direct aspect (axis parallel to the Earth axis)
- transversal
aspect (axis parallel to the equator plane)
- oblique
aspect (axis with any direction)
The third extrinsic category is the coincidence(the „contact“)
of the mapping surface with the
underlying Earth model:
- tangency
(„touching“)
- secancy
(„intersecting“)
