Applications; Limitations - ashtech Z-Xtreme System Manual

Applications

The two primary survey tasks for which RTK systems are used are feature location
and feature stakeout.
Using GPS RTK for feature location was briefly discussed above. With the base and
rover systems operational, a user, carrying the rover system, moves around the
project area positioning features of interest. Features of any type can be positioned,
centerline of a road, perimeter of a pond, light poles, corners of buildings, etc. Fea-
tures can include existing boundary monuments or new monuments needing to be
positioned for the first time. This capability makes GPS RTK a great tool for mapping
applications, such as topographic and planimetric surveys, and as-built surveys. RTK
systems are also very efficient for mapping stockpiles and gravel pits for volume com-
putations.
Feature stakeout is a task that can only be accomplished with GPS operating in RTK
mode. Stakeout of a feature involves stakeout of a point or series of points that define
the location of the feature. Given the coordinates of a point, you must be able to find
the exact location on the ground that corresponds to those coordinates. Convention-
ally, this is done by the total station operator directing the rod person to the correct
location through observing the rod person's current location and directing the amount
of movement to the correct location. With RTK, the rover operator can determine his/
her current location by observing the handheld computer screen. The coordinates of
the point of interest are also known by the handheld computer. With the RTK system
knowing its current location and the location of the point to be staked, the system can
direct the user to the correct location. This capability makes RTK a very effective
stakeout tool. Any object can be staked out with GPS RTK including roads, pipelines,
DTM's, grids, etc.
In most cases, an RTK system will be vastly more productive in these types of sur-
veys than a conventional total station with the added benefit that an RTK system can
be operated by only one person.

Limitations

GPS RTK does have limitations that affect its ability to perform some of the survey
tasks discussed above. Being aware of these limitations will ensure successful
results from your RTK surveys.
The main limitation is not limited to RTK but is a limitation of the GPS system in gen-
eral. 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 through objects that may
obstruct the line of sight between the satellites and the GPS receiver. Virtually any
4 Real-Time Kinematic Surveying