9 Measuring with GPS
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Incorrect location of the base station antenna
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A GPS rod bubble is out of adjustment or the rod is bent
These errors can easily be detected by rechecking the system setup. After starting the rover each
day, the software prompts you to recheck the system setup. All recheck system setup operations
are logged in the work order report and record files for reference and troubleshooting
requirements.
Measuring a new control point
There are several reasons why you may need to measure a new control point during a project and
then add the measured position to the control point file for the site. Typical cases include:
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When operating the project with a mixture of GPS and total station equipment; total stations
require more control points around the project because of their line-of-sight dependence.
Control points can be established very rapidly using GPS and can be used later by total station
crews to establish their position and orientation.
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When operating a site, a base station often needs to be moved closer to the current working
location to provide better radio coverage. The base station must be relocated to a known point
in the local coordinate system. Using the Measure control point option ensures that the point
is created in the correct location, with the correct coordinates, and guarantees that the site
calibration remains valid after the base station is moved.
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When carrying out topographic measurements on a new site before control for the project is
established, you may set the base station up in an arbitrary and convenient location and then
carry out a single-point calibration. Once completed, measuring three or more control points
around the project provides a common set of reference points that can be used later to
transform the data measured using the single-point calibration, to the site coordinate system
once it is established.
1. From the Home menu, tap either GPSor Total Station and then tap Measure Control Point.
2. Create the control point location using a stake, a hub, or a road nail as required and then mark
the stake with the name for the control point, for example, STNQ.
3. Set up the GPS rod over the point and hold it steady using a bipod. The software displays the
current GPS position on the map.
4. When you are ready to take the measurement, tap Measure. The measurement process takes
approximately 15 seconds to complete. Measuring for 15 seconds takes an average position
that increases the accuracy of the computed control point.
When each control point is measured, the software stores the control point data position in the
control point (Control.csv) file for the site, and also records the measurement data into the record
and report files for the work order.
Trimble SCS900 Site Controller Software User Guide 89
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