SX BLUE GPS iSXblue II+ GNSSTM, Руководство пользователя

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SXblue Series User Manual 62
For example, if Product A after test results in an accuracy of 90 cm 95% (R95) and
you want to compare this to Product B that has a sub-meter horizontal RMS
specification, select the value from where the ‘R95’ row and the ‘RMS’ column
intersect (to convert to RMS). You will see that this conversion value is 0.59.
Multiply the 90 cm accuracy by this conversion factor and the result will be 53 cm
RMS. If you now compare this to Product B’s specification of sub-meter RMS, you
can see the Product A would offer better performance. To properly evaluate one
receiver against another statically, they should be using identical correction input
(from an external source) and also share the same antenna using a power splitter
(equipped with appropriate DC-blocking of the receivers and a bias-T to externally
power the antenna). With this type of setup, the errors in the system are identical
with the exception of receiver noise.
Although this is a comparison of the GPS performance quality of a receiver, it
excludes other performance merits of a GPS engine. The dynamic ability of a
receiver should be compared in a similar way with the test subjects sharing the
same antenna. Unless a receiver is moving, its software filters are not stressed in
a similar manner to the final product application. When testing dynamically, a much
more accurate reference would need to be used, such as an RTK system so that
a ‘truth’ position per epoch is available.
Further, there are other performance merits of a GPS engine, such as its ability to
maintain a lock on GPS and SBAS satellites. In this case, the same GPS antenna
should be shared between the receiver test subjects. For the sake of comparing
the tracking availability of one receiver to another, no accurate ‘truth’ system is
required, unless performance testing is also to be analyzed. Again, an RTK system
would be required; however, it’s questionable how its performance will fair with
environments where there are numerous obstructions, such as foliage. Other
methods of providing a truth reference may need to be provided through
observation times on surveyed monuments or traversing well-known routes. Again,
be aware that the coordinates output by the SXblue receiver, with no differential
correction, are in the current GPS WGS84 (G1674) datum (which follows ITRF
2008, epoch 2005).
The GPS antenna included should be mounted pursuant to the following
requirements:
•
The SXblue receiver computes a position based upon measurements from
each satellite to the location of the GPS antenna’s phase center. Mount the
GPS antenna in the location for which you desire a position. When choosing
a location to mount the antenna, please ensure that there is an unobstructed
hemisphere of sky available to the GPS antenna. This will ensure that GNSS
and SBAS satellites are not masked by obstructions, potentially reducing
system performance.
•
It is important to locate any transmitting antennas away from the GNSS
antenna by several feet or more. This will help to ensure that tracking