Leica Geosystems GPS Basics - Manual (Page 36)

36
GPS Basics -1.0.0en Geodetic Aspects
0
N
E
The False Easting and False Northing
are defined in order that the origin of the
grid projection can be in the lower left
hand corner as convention dictates. This
does away with the need for negative
coordinates.
The Latitude of Origin defines the
Latitude of the axis of the cylinder. This is
normally the equator (in the northern
hemisphere).
The Central Meridian defines the
direction of grid north and the longitude
of the centre of the projection.
Scale varies in an east-west direction. As
the cylinder is usually smaller than the
spheroid, the Scale on Central Meridian
is too small, is correct on the ellipses of
intersection and is then too large at the
edges of the projection.
The scale in the north-south direction
does not vary. For this reason, the
Transverse Mercator projection is most
suitable for mapping areas that are long
in the north-south direction.
The Zone Width defines the portion of
the spheroid in an east-west direction to
which the projection applies.
Features of the Transverse Mercator projection
Universal Transverse Mercator (UTM)
The UTM projection covers the world between 80ºN and 80ºS latitude. It is a
type of Transverse Mercator projection, with many of the defining parameters
held fixed. The UTM is split into zones of 6º longitude with adjacent zones
overlapping by 30’. The one defining parameter is the Central Meridian or
Zone Number. (When one is defined, the other is implied).
Zone Width
Central Meridian
Ellipses of
Intersection