Observations and Measurements

In FreeFlyer, an Observation represents a collection of Measurements taken at the same time. The observer and object being observed are the same for all the Measurements in a given Observation. Each Measurement contains its own statistics, such as pre- and post-update residuals. Currently, FreeFlyer supports several types of Observations, each with different available Measurements:

[1] Note: Ground Station observations and DSN observations support both 2-way and 3-way Doppler measurements. See Simulating 3-way Observations for more information.

At the Observation level there are multiple "Use" flags corresponding to the available measurement types for that observation. When simulating an observation, these flags control whether or not the particular measurement is simulated. When processing an observation, these flags control whether or not the measurement is processed by the estimator. For example, if the UseRange property of the GroundStationObservation object is set to 1 (true), then the range measurement will be simulated when the Spacecraft.SimulateTrackingData() method is called and processed when the Observation object is processed using a KalmanFilterOD, SquareRootInformationFilterOD, UnscentedKalmanFilterOD, or BatchLeastSquaresOD object.

Each Measurement includes the following properties:

Each of these properties is read-only, with the exceptions of the Observed Value and the Validity flag. The read-only properties are automatically set when a Measurement is processed by a KalmanFilterOD, SquareRootInformationFilterOD, UnscentedKalmanFilterOD, or BatchLeastSquaresOD object.

These properties can be used to gain insight into the state estimation process. For example, in the following script a Measurement's pre- and post-update residuals are inspected:
 

See Also