ashtech HDS800, Справочное руководство

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622
Troubleshooting
Step 2. Are the
Base and Rover
Tracking at least 5
common
Satellites?
Although the rover is capable of computing a position with
only 4 common healthy satellites with the base, the rover will
not attempt to fix ambiguities unless 5 common healthy
satellites are observed. Fixing ambiguities is a required
process for the rover to compute highly precise RTK positions.
The receiver will inform you if you currently have a fixed
ambiguity solution or a float ambiguity solution. Your field
application software will also inform you which satellites are
being tracked by the base and which are being tracked by the
rover and whether or not these satellites are healthy. If you
find that your solution will not fix, look to determine if the
base and rover are indeed tracking at least 5 common healthy
satellites.
1. If the base and rover are not tracking at least 5 satellites :
• Check satellite availability. Use the Mission Planning
utility from GNSS Solutions to check satellite
availability for your current location and time. Look for
the number of satellites higher than 5° above the
horizon. Ensure at least 5 healthy satellites are
available. If not, you will need to perform your survey
at another time.
Go to step 3 below if the problem is not yet resolved.
• Move the base or rover if sites have satellite
obstruction. If your base or rover site has any
obstructions higher than 5° above the horizon, the
obstructions may be blocking essential satellites. If
obstructions exist at the base or rover, move the system
to an open area.
Go to step 3 below if the problem is not yet resolved.
2. If the base and rover are tracking at least 5 satellites , go
to step 3 below.
Step 3. Are HDOP
& VDOP Values Too
High for Precision
Requirements?
Dilution of Precision (DOP) values give a quality indication of
the satellite geometry at any given time. Satellite geometry is
important to the precision of an RTK solution.
In fact, the DOP value is used as a multiplier in the
computation of position precision. For example, in the
computation of horizontal RMS (HRMS), an estimated
precision value is multiplied by the HDOP at that given time
to produce HRMS. The larger the HDOP value, the larger the
HRMS value. The same relationship holds for VDOP and
VRMS.