Piksi® Multi (firmware v1.1 and newer) supports observation and navigation data conversion to RINEX (Receiver Independent Exchange) format and data post-processing using third-party tools.
The SBP (Swift Binary Protocol) to RINEX converter (sbp2rinex) is available for Windows, Linux and OSX computers. Executables can be downloaded from here and source code is available through Swift’s fork of RTKLIB’s convbin on Github here.
The sbp2rinex converter is a command line tool. It can convert SBP binary or SBP JSON logs. Log type is recognized by the file extension: .sbp - binary SBP, .json - SBP JSON.
sbp2rinex [option ...] file
To display all options and help information launch converter with -h option.
Note: use converter with live data only. Log from Piksi Multi in the simulation mode will not convert as expected.
sbp2rinex -v 2.1 swift-gnss.sbp.json - converts JSON SBP file to RINEX version 2.1 files
sbp2rinex swift-gnss.sbp - converts binary SBP file to RINEX version 3.0 files
sbp2rinex -h - displays usage help
Fig. 1. sbp2rinex execution on Windows PC
Required SBP messages
In order to produce Rinex data, it is necessary to have raw observables and ephemerides. Make sure that the all of the SBP messages in the table below are enabled through the recording interfaces. The SBP messages are can be configured through the “enabled_sbp_messages” setting on each interface.
|Message Name||Message ID (decimal)||Notes|
|MSG_BASE_POS_ECEF||72||Base station surveyed position (if entered). Not currently in use by converter but may be used in future.|
|MSG_OBS||74||Raw measurements from any constellation|
|MSG_IONO||144||Broadcast Ionospheric Delay|
Table 1: Required SBP messages for valid RINEX
The RINEX file(s) generated by the sbp2rinex converter can be used by third-party post-processing tools like RTKLIB (http://www.rtklib.com/) or online PPP services.
RTKLIB RTKPOST tool can be used to compute RTK solutions from observations collected by Swift Navigation Piksi Multi receiver.
Fig. 2. RTKPOST use example
Fig. 3. Sample output
Sample files used for above example are available here.
Online PPP Post-processing
Online PPP services like OPUS (https://www.ngs.noaa.gov/OPUS/) and AUSPOS (http://www.ga.gov.au/bin/gps.pl) can be used to compute stationary RTK solution from observations collected by Swift Navigation Piksi Multi receiver. These services can be used to determine the surveyed position of a Piksi Multi being used as a base station and are recommended rather than the “Auto Survey” method for applications where accuracy with respect to a map is important such as surveying. Follow instructions on the PPP service web site for data file requirements and limitations.
Piksi Multi uses GPS L2C signals. Some online services (eg. AUSPOS) are not supporting L2C measurements. A simple change in RINEX file may allow data processing. Change line
8 C1 L1 D1 S1 C2 L2 D2 S2 # / TYPES OF OBSERV
8 C1 L1 D1 S1 P2 L2 D2 S2 # / TYPES OF OBSERV