SXBlue II GPS Series Technical Reference Manual
31
The position excursion from the true position (the lines centered on the zero axis are Northing
(blue) and Easting (pink)) with increasing correction age is smooth from position to position, but
you can see that there is a slow drift to the position. The amount of drift will depend on the rate
of change of the environmental errors and how these change from the models used inside the
Auto-Dif software engine.
It’s up to you for how long you would like Auto-Dif to function before performing another
calibration. We recommend that you test this operating mode to determine the level of
performance that’s acceptable to you.
Please contact Geneq for more information on this feature.
2.6.4 Local Differential options
Local differential is a specialized message type that can only be sent between two SXBlue II
GPS receivers. One receiver is used as the base station and must remain stationary. It is
extremely useful to know the coordinates of the base station position, but averaging the position
will also suffice. The second receiver is used as a rover and the messages must be sent
through a communication system. Various types of radio-modem technology are available
(UHF, 900MHz, 2.4GHz, cellular, etc) to suit the application.
The Local Differential applications come in three versions:
•
Local-Dif Rover for a 20cm floating solution
•
Local-RTK Rover for 1-3cm fixed single frequency RTK solution with OTF (On-The-Fly)
capability
•
Local-Base, Base Station Application to support both Local-Dif and Local-RTK
For the RTK application, the baseline length (distance between base station and rover) should
be kept short (less than 10km). The positioning performance of the receiver in Local-Dif and
Local-RTK modes is dependant upon the environment of the base and rover receivers, the
distance between them and the accuracy of the entered coordinates of the base station. We
suggest that you perform your own testing at your location to determine the level of performance
that you would expect to see on average. When testing this feature, it is a good idea to look at a
lengthy test of 12-24 hours, in different environments, and monitor performance against a
known coordinate.
2.7 Post Processing
The SXBlue II GPS receiver is able to output raw measurement data for post processing
applications. The raw measurement and ephemeris data are contained in the Bin 95 and 96
messages documented in chapter 5. Both messages must be logged in a binary file. For cm-
level post-processing, a survey grade L1 antenna with ground plane is highly recommended and
software that processes the carrier phase should be used.
A DOS-based RINEX translator is available; however, RINEX has no facility to store station
information. Please contact Geneq if you wish to use this utility. Off-the-shelf software is
available for collecting and post-processing SXBlue II GPS raw data.
