Spectra Precision Survey Pro CE v3.60 GPS User Manual - Manual (Page 17)

GPS Coordinates
13
Fig. 3: Transverse Mercator Mapping Plane
A side view of the cylinder shows the effect of scale
distortion.
El
l ip
so
id
Mapping Plane
K=0.9996
K=1.0 K=1.0
Central Meridian
K>1.0 K>1.0 K<1.0
Distance on Ellipsoid
Distance on Map
• Universal Transverse Mercator
Projection
The scale factor at the central
meridian (CM) is 0.9996. The
scale factor is 1.0 approximately
170-km east and west of the CM.
The scale factor is less than one
between the CM and the point of
tangency. The scale factor is
greater than one beyond the point
of tangency. Therefore, at the
central meridian, a geodetic
distance of 100m scales into a
mapping plane distance of
99.96m.
• TDS Localization Stereographic Projection
The scale factor at the start location (usually the first
GPS base station in a project) is calculated for
ground distances at the base height. The scale factor
increases more or less uniformly in all directions as
you move away from the base. The scale factor does
not change appreciable within the range of RTK
GPS, so this map projection is an excellent way to
model simple flat earth ground level
coordinate systems.
Ellipsoid
Terrain
h
Mapping
Plane
Fig. 4: Localization Stereographic Mapping
Plane
A side view of the ellipsoid and
stereographic mapping plane show the
scale calculated for ground distances at
the base height.