Spectra Precision Survey Pro v4.2 GPS - Manual (Page 8)

6
Start GPS Survey - Choose Projection Mode
If you are not starting a new job with one point setup, you
need to choose one of two projection modes: Ground TDS
Localization
, or Mapping Plane. Choose to Use Ground TDS
Localization> if your local coordinate system is a ground level
survey, with no projection and no datum to define the
relationship between geodetic and local positions. Choose to
Select a Mapping Plane Zone> if your local coordinate system
is defined by a conformal map projection and geodetic datum
which you can choose from the database. The two projection
modes are described below:
Ground TDS Localization Mode
In this mode, a default map projection is created with your
first base setup. This default map projection is scaled for
ground distances at the base height. You then collect GPS
measurements on local control points and solve the
localization adjustment. The localization adjustment is a 2D
similarity transformation which translates, rotates and scales
the default map projection’s (y,x) into your local coordinates
(N,E).
Mapping Plane Mode
In this mode, you setup a conformal map projection with a
geodetic datum. This map projection and datum define the
relationship between the geodetic positions (LLh) from the
GPS receiver and local coordinates (N,E,Elev). You can select
a mapping plane zone and geodetic datum from the coordinate
system database, or you can key in your own custom
projection.
After selecting a mapping plane zone from the database, if
your RTK base is set on a known location, no additional steps
are necessary to solve the coordinate system. However, if your
base is set at a new point, and the survey was started from an
autonomous GPS position, you will need to solve a localization
adjustment for the mapping plane. The mapping plane
localization adjustment is a 2D similarity transformation
which translates, rotates and scales the inaccurate map
projection coordinates calculated from your autonomous base
setup into the correct coordinate system.