Measurement Processing

Measurement Types

The MeasTypes property specifies the list of specific measurement models that may be used for the estimation process. If specific measurement types are included in this list, any measurements of types not included will be discarded during the estimation process. An empty MeasTypes list is equivalent to including ALL measurement types.

Note that in version 6.1, the default behavior is to create an empty list, which now has the same behavior as including all measurement types. If you want to turn off all measurement types for a Facility, Satellite or GNSSSatellite object, set the AllowMeasProcessing flag to false.

WARNING: The MeasTypes list on a Facility or Satellite, if not empty, must contain the types of measurements to be processed from a GNSS Receiver attached to that Facility or Satellite. Measurements of types not included in this list will not be processed during estimation even if the associated measurement statistics are defined in the GNSS Receiver.

NOTE: The contents of the MeasTypes list are not related to the contents of the MeasurementStatistics list, which specifies the types of measurements that may be made of other objects from this facility or satellite.

Click to the right of the MeasTypes attribute to display a List dialog that enables you to add and remove any or all of the measurement types that are listed. To add measurement types, click the Add... button to display an Add List dialog, in which you can select the items you want to add. To delete an item, select it in the List dialog and click the Remove button. A Remove All button is available for deletion of all measurement types.

TIP: When selecting items in the Add List dialog, you can use multi-select techniques with the CTRL and SHIFT keys.

Selection of pseudo-range and phase count measurement types has certain implications to the simulator and filter processes. The following table shows the results of selecting various measurement types for the case where the measurement type list in the facility or satellite is the same as that in the filter

Results of Selecting Various Pseudo-Range Measurement Types
MeasType Simulator Filter
CA Generated Processed if SD CA not selected
SD CA ... Processed
P1 Generated Processed if DF and SD DF not selected
P2 Generated Processed if DF and SD DF not selected
DF ... Processed if SD DF not selected
SD DF ... Processed

Results of Selecting Various Phase Count Measurement Types
MeasType Simulator Filter
LA Generated Processed if LA SD not selected
SD LA ... Processed
L1 Generated Processed if DF , SD DF , SD L1 and SD L2 Phase not selected
L2 Generated Processed if DF and SD DF, SD L1 and SD L2 Phase not selected
DF Phase ... Processed if SD DF and SD L1 and SD L2 Phase not selected
SD DF Phase ... Processed if SD L1 and SD L2 Phase not selected
SD L1 and SD L2 ... Processed

As can be seen from the above tables, the processing of derived measurements takes precedence over the processing of raw measurements. This allows you to perform, for example, analyses in which you simulate CA pseudo-range measurements and process SD CA pseudo-range measurements without having to change the selected measurement types.

NOTE: To process any measurement type, including the singly differenced measurement types, the associated measurement statistics must be defined in the GNSS receiver.

The measurement types that will be processed in a particular filter run can be determined by the measurement types that are selected both in the facility or satellite list and in the filter list. If a derived measurement type is selected in the facility or satellite, but not in the filter, then the associated raw measurement type(s) will not be processed in the filter. For example:

Editing Flags

Tracking data can be edited by the filter for a variety of reasons. The following two-character codes are included in the databases for reports and graphs, indicating the editing action taken by ODTK. Short titles are used in some of the available report styles.

Note: The codes "A " and "U " must include a blank space after the initial letter (because the codes require two characters)

Editing Flags
Code Short Title Description
"A " Accepted Accepted.
"AD" Accept High Residuals accepted via the Dynamic editing criterion.
"DN" Down Angle Angle between direction to satellite and radar face normal exceeds maximum angle down.
"ED" Resid High Dynamic editor is enabled and residual is still rejected because sigma is above the upper limit of the dynamic editor.
"FR" Forced Rej

Measurement is one of the first N in a pass, and is rejected by user specification to ignore the first N measurements in a track. This option is initially limited to TDRS 4L and BRTS data. Some typical cases in which this flag will appear:

  • When processing TDRSS 4L and BRTS measurements. The rejected measurement is one of the first N in a pass, and is rejected by user specification to ignore the first N measurements in a track.
  • When processing GNSS measurements. The rejected measurement is outside of the GNSS satellite's field of view (as specified in the PRN list on the GNSS constellation object).
"GP" GNSS Source Error GNSS satellite ephemeris not defined at current time.
"HE" High El Rejected for violation of facility or sensor constraints.
"IT" Invalid Tracker The tracker is invalid in the sense that measurement statistics are not defined for the provided measurement type. For example, if a range measurement is being processed for a tracker which doesn't specify range measurements in it's Measurement Statistics properties, then the measurement will be rejected with an "IT" flag.
"LE" Low El Rejected for violation of facility or sensor constraints.
"LG" Low Graze Rejected for satellite-to-satellite signal path passing below a minimum altitude.
"ME" Measurement Exclusion Rejected due to time falling within instant maneuver exclusion interval.
"ND" No Doppler The range is invalid if there is no Doppler measurement reported. This option is initially limited to TDRS 4L and BRTS range.
"OB" Masked Measurements are rejected if they are out-of-bounds with respect to the facility mask. The residuals are not computed.
"PE" Pole Excl Edited angles data collected too close to elevation of 90 deg or a Right Ascension of 90 degrees.
"RE" Residual The filter rejected the residual based on residual magnitude versus covariance.
"SN" SNR GNSS receiver reported SNR below analyst-selected cutoff.
"SR" Satellite Reference Ephemeris Satellite ephemeris not defined at current time - for case where satellite orbit is not estimated.

A reference ephemeris does not need to span the entire simulation interval to be used in simulating measurements if a custom simulation schedule is used that restricts the simulation of measurements for the satellite using the reference ephemeris to be within the span of that ephemeris. When this situation occurs, the state history and generated ephemeris file from the simulator for the satellite of interest will indicate a constant position and velocity for the satellite during period outside the span of the reference.

"TR" Tracker Reference Ephemeris Tracker ephemeris not defined at current time.
"U " Unknown A catch-all for a variety of extremely rare errors.
"WN" Invalid WN An invalid white noise can arise if the noise statistics are embedded in the tracking data and an invalid number is encountered (e.g. a negative number).

If a residual type is rejected because of designation under the RejectMeasTypes attribute, it will nominally be designated as RE, but the residual is evaluated against other rejection conditions and can be labeled with most of the other codes.

Additional Parameters

The measurement processing settings for a facility or satellite include, in addition to the above, the following parameters:

Measurement Processing Parameters
Parameter Description
TrackingID Enter an integer representing the tracking ID.
TrackingIDAliases See description.
AllowMeasProcessing For Facility, Satellite and GNSSSatellite objects, set to false to turn off all measurement types.
MeasTypes Select each measurement type to be processed. An empty MeasTypes list is equivalent to including all measurement types.
MinPassDelta Enter a time value to define the minimum interval between measurements to constitute a new pass.

ODTK 6.5