Custom Tracking Intervals
The CustomTrackingIntervals option enables you to define inclusion and exclusion periods and increased time steps for all or selected satellites and facilities.
Click the Schedule property to display a List window in which you can add, edit, and remove custom tracking intervals. When you click , a line appears in the list in which you can add the time step and inclusion/exclusion intervals for selected satellites and trackers. To edit this line, click in each field and select or enter the appropriate information.
| Tracking Interval Definition | |
|---|---|
| Field | Description |
| Enabled | Set this to true to apply the selected intervals to the selected assets. |
| OverrideValidity | Set this to true to ignore most validity checks that take place when generating measurements. This is a convenient way to bypass constraints like visibility, elevation, low altitude, low SNR, and exclusion angles. Overriding is only available when Enabled is true. |
| PrimaryObjects | Select from the following options:
See the note below regarding the simulation of ground-based tracking data to GNSS satellites with orbits that are not being estimated. |
| SelectedObject | If you set PrimaryObjects to Specific Satellite, Specific SurfaceVehicle, or Specific Emitter, then select the object to which ODTK will apply the intervals. |
| Trackers | Select between All Trackers and Specific Tracker. Because each tracking strand contains specific tracking elements, Specific Tracker is an activator for the SelectedTrackingStrand option. After opting for Specific Tracker, you can make the tracking strand listing visible by clicking below the SelectedTrackingStrand header. Then, from the list of relevant tracking strands, you can select the strand containing the specific tracking elements to which the custom tracking intervals would apply. |
| SelectedTrackingStrand | Select the tracking strand to which ODTK will apply the intervals. |
| TimeStep | Enter the time step in the desired unit. The default is the simulator value for TimeStep. |
| InclusionIntervals | The List dialog box that appears will contain a line for the definition of the inclusion interval. Click to insert additional subintervals. On each line, set the Enabled value to true if the subinterval is to apply; otherwise set it to false. Edit the Start and Stop times as desired. The first interval added has a default span based on the scenario's DefaultTimes.Intervals.TimeSpan attribute. To delete a line, select it and click . To clear the list, click . |
| ExclusionIntervals | Set exclusion intervals in the same way as inclusion intervals (see earlier). |
To delete an interval, select it and click . To clear the list, click . To reorder intervals, select one in the list and click or .
There are two alternative methods to define custom tracking intervals:
- You can define custom tracking intervals by using a link to an Interval File in an external (*.int) file and link to it. Click where indicated next to the IntervalFileLinks attribute. In the List dialog box that appears, add lines and manage them as described above for the Schedule attribute. Here, instead of defining an interval manually, you specify the path and file name of the file where the interval is defined. The LinkedSchedule attribute displays a read-only list of the schedule defined via the IntervalFileLinks mechanism.
- You can define custom tracking intervals by reading in the measurement information from the Scenario.Measurements.Files. This option is controlled by the "ImportMeasFileSchedule" property. When set to true, a Tracking Interval definition is created for each enabled {Satellite, Tracker} present in the measurement files. An InclusionInterval will be added for each measurement time. You can display the read-only measurement file schedule by clicking the ImportedSchedule property. Be aware, however, that the displayed schedule only "data limits" the custom tracking intervals by the objects that are contained within the scenario, whereas the resulting simulated measurements are "data limited" by the Simulator SatelliteList, EmitterList, TrackingStrandList, and MeasurementTypes list.
The simulator's TimeStep property sets the limit on the degree of fineness of measurements taken during the simulation. Setting the TimeStep field in the List window to a smaller time span than the TimeStep you defined for the simulator has no effect. If you set the TimeStep for the interval to a time span larger than the simulator's TimeStep but not a multiple of the latter, the actual time span applied will be the next-higher multiple of the simulator's TimeStep. For example, if you set the simulator's TimeStep to 15 minutes and set the TimeStep in the custom interval to 20 minutes, measurements during the interval in question will be taken at times 0 minutes, 30 minutes, 60 minutes, etc.
If GNSS satellites are defined to estimate the orbits of the satellites, you can use them in tracking data simulation in the same manner as normal satellites. If the GNSS satellites are defined to obtain their ephemeris information from a GNSS reference file, then the simulator will only generate ground-based tracking data to the GNSS satellites if the GNSS satellites of interest are included individually in custom tracking intervals. For example, to generate ground-based tracking data to PRN01 when PRN01 is defined to obtain its ephemeris information from an SP3 file, you must add an entry to the custom tracking schedule that specifies the Satellites option as GNSS Constellation and the SelectedSatellite option as PRN01. GNSS constellations that do not have populated GNSS satellites under them cannot be used to generated ground-based tracking data.
You can customize the schedule of GNSS Satellites tracked by GNSS Receivers through the SatelliteSelection properties on the GNSS Receiver. Options for controlling the PRN selection for measurement selection include (1) the minimization of GDOP, (2) following an explicit, externally generated schedule, (3) following the schedule from an assigned tracking data file, and (4) using a custom algorithm via a plugin interface.