Applications; Limitations - Thales Z-Max Operation And Application Manual

To accomplish the post-processing, data is downloaded from each GPS receiver into
the computer. The processing software utilizes this data to calculate vectors between
all GPS receivers operating simultaneously. The vectors define the 3-dimensional
relationship between the GPS receivers. From these vectors, coordinates are
determined for all points in the project, based on the coordinates of one or more
known points. If the survey included any redundant observations (closed loops, repeat
observations), then a least-squares adjustment can be performed to help identify any
blunders in the data and improve on the final point positions. The capability to perform
a least-squares adjustment is included with the GNSS Studio post-processing
software package.

Applications

Post-process GPS is well suited for most surveying tasks. Systems are being used
today for control establishment, boundary surveys, and mapping applications such as
topographic, planimetric, and as-built surveys. Post-process GPS is also very efficient
for volumetric measurements such as stockpiles and gravel pits.
In many cases, a GPS system will be vastly more productive in these types of surveys
than a conventional total station, with the added benefit that a GPS system can be
operated by only one person.

Limitations

GPS surveying systems have limitations that affect their ability to perform some of the
survey tasks discussed above. Being aware of these limitations will ensure successful
results from your GPS surveys.
The main limitation is not confined to post-process GPS but is a limitation of the GPS
system in general. As discussed earlier, GPS depends on reception of radio signals
transmitted by satellites approximately 20,000 km from earth. Being of relatively high
frequency and low power, these signals are not very effective at penetrating objects
that may obstruct the line-of-sight between the satellites and the GPS receiver.
Virtually any object that lies in the path between the GPS receiver and the satellites
will be detrimental to the operation of the system. Some objects, such as buildings,
can completely block the satellite signals. Therefore, GPS can not be used indoors.
For the same reason, GPS cannot be used in tunnels or under water. Other objects
such as trees can partially obstruct or reflect/refract the signal, so that reception of
GPS signals is very difficult in a heavily forested area. In some cases, enough signal
can be observed to compute a rough position, but in virtually every case, the signal is
Introduction 99