How to Configure Arrow for SBAS with Eos Utility

How to Configure Arrow for SBAS with Eos Utility

You should have received your Arrow loaded with factory-default settings to suit most applications. No other setup is required for typical SBAS operation. This section covers some basic configuration parameters of the Arrow using Eos Utility for Windows.

Launch Eos Utility, set the connection type to “Serial” and select a COM port to communicate with the Arrow (via USB or Bluetooth; see previous section for setting up connectivity). If connecting via Bluetooth, baud rate selection is not necessary. If using USB, on the contrary, a baud rate must be selected. The factory default for the USB port is 19200 baud. If the baud rate was changed, selecting the “Auto-baud” will automatically detect the baud rate and connect to the Arrow.

There are two modes available in Eos Utility: “Quick Config” and “Advanced”.

Quick Config Mode allows full configuration of the Arrow parameters and of the messages to be output on the Bluetooth and USB ports. Data Logging, RINEX conversion, NTrip client are other features available in this mode.

Advanced Mode includes all the features of Quick Config and adds display of diagnostic information (Position and satellite, statistics, etc), base station and LBand/Atlas configuration. Advanced mode activates some binary messages on the communication port to operate properly and it is recommended to set a higher baud rate if connecting via the USB port (57600 or 115200 is suggested). To change the baud rate after connection, select the USB port tab, set the baud rate to the desired value and select File/Save settings.

The screen below shows the factory-default configuration for your Arrow. The following is a brief description of each parameter along with some suggestions for other values for SBAS operations. (Please note that Eos Utility includes factory default configuration files. They can be found in the following menu “File”/”Load Configuration File” and select the config that best suits your application.)

• Diff Source. This value should be set to SBAS. The Arrow will automatically detect the SBAS constellation available in your area and use it.
• Diff Age expressed in seconds, is the maximum age of differential correction the Arrow is allowed to use after losing the SBAS signal. For forestry applications, a default value of 3600 is suggested. Since the Arrow is able to maintain submeter accuracy 30 to 40 minutes after the loss of differential correction, a value of 1800 to 2700 seconds is suggestion for multipath free environments.
• Elevation Mask is the minimum elevation angle for a satellite to be used. Lower elevation satellites might cause some multipath error in the position computation. Suggested values are 5 or 10 degrees.
• Decimal Precision is the number of decimal digits for Latitude and longitude minutes reported in the GGA , GLL and RMC NMEA sentences. Default value is 7.
• Smoothing Time in seconds is the refresh rate of the carrier phase smoothing. Default value is 900 seconds (Long).
• Altitude Aiding Mode. In order to compute a position, a receiver must know its elevation. Either it computes it on its own (elevation inaccuracy is in general 2-3 times that of horizontal and by rule-of-thumb, a 1/3 of that vertical error is applied to the horizontal position) or it is set manually by the user. The advantage of this feature, when operating in an application where a fixed altitude is acceptable, is that the extra satellite’s observations can be used to the betterment of the latitude, longitude, and time offset calculations, resulting in improved accuracy and integrity. Marine applications, for example, may be well suited for use of this feature. Possible values for this parameter:

NEVER (3D ONLY): receiver computes its own elevation and Aiding is not used. For multipath free/non-forestry environment, this should be the default.

SOMETIMES (PDOP): if PDOP is higher than the value specified in “Altitude Aiding Value” (see below), then the receiver switches to 2D mode and uses an average of previously computed elevations. This is the default for the Arrow and the Aiding value for PDOP is set to a loose 10.5 for forestry applications.

AUTO 2D/3D. In this mode the Arrow switches between 2D and 3D positioning based on the number of available satellites. Usually, if there are less than 4 satellites, the Arrow switches to 2D mode.

SATS. Sets the Arrow to use altitude aiding depending upon the number of visible satellites. If there are fewer visible satellites than specified in the “Altitude Aiding Value”, altitude aiding is used.

ALWAYS. Sets the Arrow to always use altitude aiding regardless of the other variables. In this case, you must specify the ellipsoidal altitude that the receiver should use in the “Altitude Aiding Value” field. Remember that a wrong values of ellipsoidal height will greatly affect the horizontal positioning.

• Altitude Aiding Value. Specifies the value for Altitude Aiding Mode (PDOP for SOMETIMES, Number of satellites for SATS and Ellipsoidal Height for ALWAYS modes).
• RESID Limit sets in meters the threshold of estimated horizontal performance for which the DGPS position LED is illuminated. This parameter only has an effect on the Arrow DGPS LED. Default value is 10 meters.
• GPS Only Mode set to “YES” forces the Arrow to use only the GPS constellation for position computation, regardless of the availability of GLONASS, BeiDou, Galileo or QZSS satellites.
• Forest Mode enables or disables high gain functionality for tracking under forest canopy. Factory default is YES
• Null NMEA Mode enables or disables null fields in NMEA messages when there is no fix being computed by the Arrow. If this setting is disabled and position is lost then the positioning parameters of the message from the most recent known position are repeated (instead of being NULL if enabled). Default values is YES.
• TunnelMode enables/disables faster reacquisition after coming out of a tunnel. Default is NO.
• SBAS Ranging Mode specifies whether the Arrow uses the ranging feature of some SBAS constellations to compute the position. In other words, SBAS satellites are used as “extra” GPS satellites. Default values is YES. Note that the European EGNOS satellites do not offer ranging information, therefore it is preferable to set this value to NO when using EGNOS.
• Mixed Mode Include satellites that do not have SBAS corrections in the solution. This command is useful if you are trying to maximize the likelihood of calculating a position, but are willing to sacrifice some accuracy. Default is YES.
• Timekeep Mode enables/disables continuous time updating in NMEA 0183 messages when there is no fix (when position is lost). When position is lost, time is the only parameter in the message that continues to update; all other parameters remain the same. Default is YES.
• L1 Only Mode has no effect on SBAS operations or with the Arrow Lite and 100 models. This parameter will be covered in the next chapter.
• Suretrack Mode enables or disables SureTrack functionality in which the Arrow tries to compute internal differential correctors for other constellations based on the corrections it receives for GPS from the SBAS satellites (remember that all SBAS only broadcasts correctors for the GPS constellation only). Default is YES. For forestry applications, set this value to NO.
• GGA ALL GNSS Mode. This parameter configures the GGA string to include full GNSS information (the number of used satellites in other constellations will be included in the GPGGA message). The GGA message is only supposed to report position and satellite information based on the GPS constellation. The combined GPS, GLONASS and BeiDou position and satellite data should be reported in the GNSS message, but some users with older equipment/software cannot utilize this message. This command allows users with older equipment that require a GGA message to be able to utilize and take advantage of satellites from all constellations. Default value is YES.
• Glofix Mode. Not used for SBAS operations. Will be discussed in next chapter.

The “Diff Includes” section lists all the possible type of differential correction sources that the Arrow can use. SBAS should be checked regardless of the other options. This topic will be covered in more details in the next chapters. Default setup has all values selected.

It is highly recommended that you leave the default messages activated for proper operation when using iOS^® devices. It may happen that the NMEA parser of older software is not able read some of the new GNSS messages or require the GLL sentence. You may verify with your software supplier and adjust the sentence activation accordingly.

GGA: Contains Position, Time, Fix Status, Differential Station ID, age of differential correction, etc

GSA: Satellites in use and DOP’s

GST: Position statistics info

GSV: Satellites in view

RMC: Position information

VTG: Velocity, Track

ZDA: Time

The following screenshots show the Arrow’s default configuration for both Bluetooth and USB ports. After the changes are made, click on File / Exit / Save Settings & Disconnect.