Coordinate Reference System (CRS)
combination of at least one coordinate system together with its
spatial datum. In a CRS, positions or locations of geographic
information are described by coordinates.
Geodetic Reference System/Geodetic Coordinate
A coordinate reference system, based on shape, size, position and
orientation of a (mathematical) reference surface, (e.g. sphere or
spheroid). It normally is defined in a superior, geocentric three-
dimensional coordinate system (for example WGS84,
Map Projection/Map Projection Coordinate
projection defines the mapping from geographic
coordinates on a sphere or the geodetic coordinates on a spheroid
to a plane. It may define
- a map
conversion between a geodetic CRS and a map projection CRS.
(e.g. sphere or spheroid) or physically (geoid) defined surface to
approximate the shape of the earth for referencing the horizontal
and/or vertical position. Each coordinate system has a
reference surface. Map projections have a mapping surface (an
extrinsic characteristic) like cylinder, cone, plane.
(Coordinate) Reference Frame
A set of
control points to realize a coordinate reference system.
Describes the fixing
(position and orientation etc.) of a CRS regarding to the real
for a geodetic reference system. Now: a spatial datum of a geodetic
- A map
projection needs information about a reference surface.
geodetic datum fixes the reference surface in space (superior
coordinate reference system).
Mapping Agencies defined their own Reference System. Different
Countries may use the same parameters of the reference surface, but
with different position and orientation!
Mapping Agencies may use different map projections, based on the
same reference system. Different map projections depend on
scale, area and distortion- charateristic needed.
map projection between countries normally need a geodetic datum
countries use a double projection for large and medium scale
mapping (e.g. the Netherlands, Switzerland, Hungary):
projection from the reference ellipsoid to a sphere
projection from the sphere to the plane.
process of changing map projection: