ashtech Reliance FS/2, Operation Manual

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Survey P
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Survey Planning 15
• Do not change the Data to Log type on the Receiver Setup screen while a
session is in progress. This setting should always be Code Only (or Code &
Carrier, depending on the receiver option you purchased) if the data is going
to be post-processed.
• If one of the above events happened, make sure to re-collect any features
of interest which were part of files which last less than 5 minutes.
Improving Feature Accuracy
The following techniques can be used while collecting feature data to measurably
improve the post-processed feature position accuracy.
• On the Datalogging Setup screen, increase the Time On Point from the
default 0.33 to one minute or more. Under heavy tree canopy or other severe
multipath environments, record at least 60 epochs for the 2-sigma filter to
work effectively. Refer to the Office User’s Guide for more information on
the 2-sigma filter.
• On the Datalogging Setup screen, decrease the recording interval if you
need line and area contours to have greater resolution or accuracy. The base
station recording interval must be less than or equal to and on an even
multiple of the rover recording interval for the processor to process every
epoch. Remember not to change the recording interval if features have
already been logged for a session; changing the recording interval forces a
new session to begin.
• Allow up to four minutes for all available satellites to lock before logging
the first feature. The number of satellites used and locked can be viewed on
the POSN screen. At least four satellites must be used. If more than four
satellites are available, wait until they are in use before logging the first
feature.
• After starting a new session, always wait at least one minute after the first
position is computed before logging the first feature. This results in greater
accuracy for the first feature. Remember if logging data for centimeter
processing, you must record data for at least 30 minutes per point.
• While a session is in progress, avoid losing lock on satellites (walking under
bridges, tipping the GPS antenna, etc.), even if a feature is not currently
being logged. This prevents gaps from occurring in the GPS data, and results
in greater feature accuracy when a feature is logged. If, for whatever reason
satellite lock is lost, stop and wait for at least four satellites to re-lock before
logging the next feature.
• Collecting data under heavy tree canopy significantly reduces the feature
accuracy if the number of satellites drops to four or fewer for more than a
minute or so. If you find this happening, move to an area of light canopy and
wait at least two minutes for five or more satellites to lock.