Initialization - Magellan ProFlex 500 Reference Manual

Precise Surveying - Field Applications & Concepts

Initialization

Preamble
306
2. If you are only interested in performing relative
measurements (i.e. positions of points relatively to other
points), then the base can be installed on an unknown
point meeting the reception requirements. In this case,
the position to be entered in the base can be accurate only
to within a few meters.
Caution! In this case, keep in mind that you will not be
able to attach your points to a known coordinate system
unless later you accurately determine one of these points
in the desired coordinate system. If you are using field
software such as Magellan FAST Survey, you can also use
the Localization function to attach your job to a local
system.
There are some disadvantages that you should be aware of
when installing a base on an unknown point. For every 15
meters of error between the estimated base coordinates
and the true base coordinates, one part-per-million (ppm)
of relative error will be introduced into the computed
vector between base and rover, plus the absolute
difference between the computed base position and the
real base position.
For example, assume that the coordinates assigned to the
base point are 30 meters off the true base position. This
30-meter offset from truth will produce 2 ppm (0.002 m
per kilometer or 0.010 ft per mile) of error in the vector
between base and rover.
If the rover is 5 kilometers (3 miles) from the base, this
will produce 0.010 m (0.030 ft) of error in the vector. In
most cases, the base receiver will estimate its position to
better than 30 meters (probably closer to 10-20 meters),
but an error of 50 meters is possible.
If you plan to use an estimated position for the base, keep
the vector lengths between the base and rover short and
ensure the added error is not significant for the survey you
are performing.
Initialization is the process through which your real-time
receiver or post-processing software can solve the integer
ambiguity inherent in the carrier phase processing.
Solving integer ambiguity is a prerequisite for the receiver or
software to be able to deliver centimeter-accurate positions.