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RTK Prep
aration
Enter Base Point ID, Coordinates, and HI Into Base Receiver
Remember that the computation of the rover position is relative to the base position.
Since the rover receiver performs the position calculation, it must know the coordi-
nates of the base point. Both horizontal and vertical coordinates are needed. By
entering these coordinates into the base receiver, they will be transmitted to the rover
along with the base receiver’s raw satellite data. The base antenna HI is used to
determine the exact location of the base antenna from the base position coordinates.
The point ID will help the rover to identify which base receiver it is receiving data from.
The HI and point ID are also transmitted to the rover system.
If you plan to set the base system on an unknown point, using the approximate coordi-
nates determined by the base receiver as the base coordinates, there are some dis-
advantages to this practice that you should be aware of. For every 15 meters of error
between the estimated base coordinates and the true WGS84 base coordinates, 1
part-per-million (ppm) of error will be induced into the computed vector between the
base and rover system. 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 (0.002m per 1 kilometer or 0.010ft per mile) of error in the vector
between the base and rover. If the rover is 5 kilometers (3 miles) from the base, this
will produce 0.010m (0.030ft) of error in the vector. In most cases, the base receiver
will estimate it’s 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.
Incorrectly entering a known base position will produce the same problem out-
lined above. It is very important that the base coordinates are checked to
ensure they are correct
.
Verify Function
Determine if the base system is functioning properly as follows:
• Determine if the base receiver is observing satellites. This can be
accomplished by either using the field application software running on the
handheld computer, or the display on the receiver.
• Determine if the base radio is transmitting data, as indicated by the
transmit LED on the base radio. This LED should flash once very time the
base radio transmits a packet of data. The default transmission frequency
is 1 second. Therefore, the transmit LED should flash once per second,
indicating proper transmission of base raw data.
The base system is now functioning as an RTK base. No further interaction with the
base is needed throughout the remainder of the survey. Figure 4.6 shows the base
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