To select a tracking data file, click the Value field. In the List dialog box that appears, click and click the FileName field. Select the desired tracking data file in the selection dialog box that appears. If you set AliasMapping strings in the Tracking ID Aliases lists for any applicable objects, then select the associated AliasMapping string from the drop-down list of choices. ODTK assembles these choices from those entered at the object level.
The AliasMapping value defaults to the last selected value. If you are going to select multiple files and want them to all use the same AliasMapping setting, set the AliasMapping prior to selecting the tracking files.
You can set default tracking data file extensions in the Plugins tab of the Options window, which is accessible from the Tools menu. You can also add your own custom scripts for loading tracking data in the Plugins tab. Set the Enabled field for each file to true or false, depending on whether you want to use it.
Round-trip representation
The RoundTripRepresentation attribute refers to ground-based range and Doppler measurements and space-based range measurements, where there is a leg from the tracker to the satellite and then another leg from the satellite to the tracker. The following options are available:
| RoundTripRepresentation Attribute Settings | |
|---|---|
| Option | Description |
| OneWay | This is the default option. It is one-half of the round-trip range, or roughly the distance between the tracker and the satellite. |
| TwoWay | This is the entire distance traveled from the tracker to the satellite and back. |
The setting for RoundTripRepresentation at the scenario level is reflected in a read-only field for range and Doppler measurement statistics and affects the numerical values displayed for the constant bias, the Gauss-Markov bias sigma, and the white noise sigma.
Look-ahead buffer size
The LookAheadBufferSize attribute is an integer with valid values from one (1) to 100000. The default value is 100. It controls the size of the internal LookAheadBuffer for each input file used for sorting observation in the time order and applying measurement models that require multiple observations. If you set LookAheadBufferSize = 1, you will effectively disable time-order sorting of the observations from each file. If you set this value too large, you will increase memory use and decrease application responsiveness when it loads large batches of observations.
Embedded white-noise sigmas
The EmbeddedWNSigmas attribute enables you to import an observation white noise sigma error statistic with each measurement from the *.GEOSC or *.navsol file types.
| EmbeddedWNSigmas Settings | |
|---|---|
| Option | Description |
| Use | Set this to true if the estimation process (Filter or Least Squares) is to use the measurement white noise statistic embedded in
the measurement file rather than the white noise value from the MeasurementStatistics table on the tracking object (Facility,
Satellite, GPS Receiver). Otherwise, set it to false.
If the input measurement file type does not include embedded white noise sigmas, then ODTK ignores this attribute. Only the *.GEOSC and .navsol file types support embedded white noise sigmas. |
| OnInputError | Applies only when EmbeddedWNSigmas.Use = true. This subattribute identifies how the estimation process should handle an invalid
white-noise sigma value input (e.g., blank, <=0, not a number).
|
View and save
The Custom Data Editing attributes provided at the scenario level enable you to tailor the reporting of measurements or the saving of measurements. When applied to the saving of measurements, these attributes enable you to define specific criteria for reducing a large tracking data file to a smaller file that contains only the data you want to process, allowing for faster processing times.
The schedule attributes are identical to those for the Filter and Least Squares objects. However, the schedule here is only applied when either viewing measurements using the View Measurements tool or saving measurements to a file using the Save Measurements tool. It does not affect which measurements would be processed in a filter or least squares run.
Additionally, one of the choices for the Action attribute is ForceReject. However, this has no effect when viewing or saving measurements, as there are no residuals to be rejected. Use the Ignore option instead.
Pass detection criteria
The ODTK application uses certain criteria to detect new passes. In addition to honoring the MeasurementProcessing.MinPassDelta setting on satellite objects, the software initiates new passes when it detects a change in the current set of objects involved in the generation of measurements. To determine the elements of the tracking strand for the ODTK software to monitor for change, choose from the following options for the PassDetectionCriterion attribute as they are available:
- Based on Scenario: The ODTK software will follow the scenario-level setting Scenario.Measurements.PassDetectionCriterion, which will be one of the options below. Based on Scenario is obviously not available in the scenario properties selection for PassSelectionCriterion.
- TrackingStrand: A change in any object in the entire tracking strand will trigger the detection of a new pass.
- TrackerAndPrimary: A change in the tracking object or the primary object, typically the target satellite, will trigger the detection of a new pass. The ODTK application maintains this method for the sake of backward compatibility of the simulator file-by-pass capability. This may result in a combining of measurements for complicated tracking strands with simple measurements, such as those involving relay satellites.
- TrackerAndSatellite: A change in the tracking object or the target satellite object will trigger the detection of a new pass. The ODTK application maintains this behavior for backward compatibility sake for the View Measurements operation. This may result in a combining of measurements for complicated tracking strands with simple measurements, such as those involving relay satellites.
The TrackingStrand option is likely preferred in most cases, but the TrackerAndPrimary option may be preferred when generating GNSS measurements from a space-based receiver. The primary object in this case is the receiver. Selecting the TrackerAndPrimary option will result in the ODTK software placing all of the measurements from that GNSS receiver into the same pass, while both the TrackingStrand and TrackerAndSatellite options would result in the software identifying individual passes for each GNSS satellite that is tracked.