Setting up an Extended Kalman Filter

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To begin configuring an Extended Kalman Filter estimation process in FreeFlyer, add a KalmanFilterOD object to your Mission Plan using the Object Browser. After double-clicking on the new object, you will see the "Estimation Model" page of its object editor. From this page, you can set initial options, such as the maximum allowable residual sigma, the step size for propagating the covariance of the filter, and whether or not to maintain a history of measurements that have been processed.


Estimation Model Page of the KalmanFilterOD Object Editor

Estimation Model Page of the KalmanFilterOD Object Editor


From this page you can also control the initial epoch for the filter, either by explicitly setting the epoch or using the epoch of a Spacecraft object. If the epoch is defined explicitly, the Epoch Details editor will be available. See Parsing Dates and Times for more information on working with the Epoch Details editor.


Epoch Details Editor for the Kalman Filter OD Object Editor

Epoch Details Editor for the Kalman Filter OD Object Editor


For information on configuring a Kalman Filter with a Smoother, see Setting up a Smoother.


You can also create and configure a KalmanFilterOD object through FreeFlyer script. The syntax example below shows how to create the object and set its initial options.


// Create and set up Kalman Filter:

KalmanFilterOD KalmanFilterOD1;

KalmanFilterOD1.MaxAllowableSigma = 6;

KalmanFilterOD1.StepSize = TIMESPAN(60 seconds);


// Set initial filter epoch:


// Specify epoch from Spacecraft

KalmanFilterOD1.InitialFilterEpochDefinitionType = 0;  



// ... or ...


// Define epoch explicitly

KalmanFilterOD1.InitialFilterEpochDefinitionType = 1;  

KalmanFilterOD1.InitialFilterEpoch = TIMESPAN(25364.5 days);


Note: As of FreeFlyer 7.3, the default timing precision mode is nanosecond precision mode. For older Mission Plans that have not yet been converted from millisecond precision mode, the syntax for working with epochs and calendar date/time strings is different. See the timing precision mode page for more information.


Once this initial setup is complete, continue configuring your OD system by:


Defining the A Priori States

Defining the Measurement Model

Defining Thrust Events

Defining the Properties to Estimate

Including Tracking Data



See Also

KalmanFilterOD Properties and Methods