GNSS Receiver: Measurement Processing

You can set the following measurement processing parameters for a GNSS Receiver object:

Measurement Processing
Parameter Description
TrackingID This is the receiver ID, which must match the "Marker Number" for the associated RINEX Observation file. ODTK checks that no two GNSS receivers have the same tracking ID. One aspect of the RINEX 3 and RINEX 4 specification for observation files that ODTK does not support is the use of EVENT records to update MARKER NUMBER and other header information. ODTK will simply ignore the information contained in EVENT records.
TrackingIDAliases See Tracking ID Aliases.
MinGrazingAlt This is the minimum grazing altitude for editing out GNSS measurements. It is available for Space type GNSSReceiver only, and is enforced during estimation and for all Satellite Selection Method options during simulation.
MinSignalToNoise

This is the minimum SNR needed to accept a GNSS measurement for processing during estimation. The simulator only uses it if the S1 parameter or SSI flags are output in the RINEX Observation file. If the SSI flags are output, ODTK maps the SSI flag value to SNR as follows:

  • 9: SNR > 500
  • 8: SNR > 100
  • 7: SNR > 50
  • 6: SNR > 10
  • 5: SNR > 5
  • 4: SNR > 3
  • 3: SNR > 1
  • 2: SNR = 0
  • 1: SNR is bad
  • 0: n/a

 
SatelliteSelection

Set the following attributes:

  • Method  - Choose a method for performing satellite selection during simulation:
  • BestNGDOP minimizes GDOP given a limitation on the number of GNSS Satellites that can be tracked simultaneously.
  • CustomIntervals uses a supplied set of intervals for each GNSS satellite.
  • ImportMeasSchedule matches the satellite selection expressed in measurement files assigned at the scenario level.
  • Plugin uses a custom algorithm via a plugin. See help on ODTK plugins for information on how to create and register a GNSS Satellite Selection Plugin.
  • RetainLast - If you set this to true, then the simulator uses the same N GNSS satellites from one time to the next so long as all N are still visible. When all N are no longer visible, the simulator determines the best N new GNSS satellites on the basis of the specified satellite selection method. The simulator uses this parameter with the BestNGDOP and Plugin Satellite Selection methods.
  • NumberOfChannels - The simulator uses this to control the number of GNSS measurements generated at any measurement time. NumberOfChannels is the number of satellites that can be tracked for each basic type of measurement statistics (i.e., any combination of CA, P1, and P2) specified for a GNSS Receiver. For example, if you set a GNSS Receiver with CA, P1, and P2 measurement statistics, and you set NumberOfChannels to 8, then the simulator can simultaneously simulate CA, P1, and P2 measurements for eight satellites. Use this setting with the BestNGDOP Satellite Selection Method; it is available from the Satellite Selection plugin interface. The simulator ignores this setting when you set the Satellite Selection Method to CustomIntervals or ImportMeasSchedule.

  • CustomIntervals.IntervalFileLinks – When you set the method for SatelliteSelection to CustomIntervals, assign interval files (.int) containing intervals for GNSS satellite selection. The simulator will select GNSS Satellites during the specified intervals as long as they satisfy the MinGrazingAlt constraint. You can view an example interval file for GNSS Satellite selection here.

  • CustomIntervals.LinkedSchedule – This is a read-only view of the satellite selection schedule generated from assigned interval files when you set the method for SatelliteSelection to CustomIntervals.

  • ImportedSchedule – This is a read-only view of the satellite selection schedule generated from tracking data files assigned at the Scenario level when you set the method for SatelliteSelection to ImportMeasSchedule. The simulator will select GNSS Satellites during the displayed intervals as long as they satisfy the MinGrazingAlt constraint.

  • PluginID - This is available if you set Method to Plugin. Select a custom algorithm from the list of registered plugins.
  • PluginConfig - This is available if you set Method to Plugin. It provides access to configurable parameters as registered by the plugin.

When using the ImportedSchedule method for Satellite Selection:

  • You should not configure the Simulator to overwrite any of the files in the Scenario measurement files list. This would result in the Simulator overwriting the measurements to be used in determining the schedule.
  • The ImportedSchedule can take some time to display since the simulator must read and parse the assigned measurement files into selection intervals.

During simulation of GNSS measurements, if a GNSS satellite selection plugin is being used, but fails, the simulator will continue with a default selection which simply picks the first four satellites. When using a GNSS selection plugin to simulate measurements, check the message viewer carefully for plugin failure messages.