org.orekit.estimation.measurements

Class GroundStation

java.lang.Object

org.orekit.estimation.measurements.GroundStation

public class GroundStation
extends Object

Class modeling a ground station that can perform some measurements.

This class adds a position offset parameter to a base topocentric frame.

Since 9.0, this class also adds parameters for an additional polar motion and an additional prime meridian orientation. Since these parameters will have the same name for all ground stations, they will be managed consistently and allow to estimate Earth orientation precisely (this is needed for precise orbit determination). The polar motion and prime meridian orientation will be applied after regular Earth orientation parameters, so the value of the estimated parameters will be correction to EOP, they will not be the complete EOP values by themselves. Basically, this means that for Earth, the following transforms are applied in order, between inertial frame and ground station frame (for non-Earth based ground stations, different precession nutation models and associated planet oritentation parameters would be applied, if available):

Since 9.3, this class also adds a station clock offset parameter, which manages the value that must be subtracted from the observed measurement date to get the real physical date at which the measurement was performed (i.e. the offset is negative if the ground station clock is slow and positive if it is fast).

1. precession/nutation, as theoretical model plus celestial pole EOP parameters
2. body rotation, as theoretical model plus prime meridian EOP parameters
3. polar motion, which is only from EOP parameters (no theoretical models)
4. additional body rotation, controlled by getPrimeMeridianOffsetDriver() and getPrimeMeridianDriftDriver()
5. additional polar motion, controlled by getPolarOffsetXDriver(), getPolarDriftXDriver(), getPolarOffsetYDriver() and getPolarDriftYDriver()
6. station clock offset, controlled by getClockOffsetDriver()
7. station position offset, controlled by getEastOffsetDriver(), getNorthOffsetDriver() and getZenithOffsetDriver()

Since:

8.0

Author:

Luc Maisonobe

Field Summary

Fields

Modifier and Type	Field and Description
static String	DRIFT_SUFFIX Suffix for ground clock drift parameters name.
static String	INTERMEDIATE_SUFFIX Suffix for ground station intermediate frame name.
static String	OFFSET_SUFFIX Suffix for ground station position and clock offset parameters names.

Constructor Summary

Constructors

Constructor and Description
GroundStation(TopocentricFrame baseFrame) Build a ground station ignoring station displacements.
GroundStation(TopocentricFrame baseFrame, EOPHistory eopHistory, StationDisplacement... displacements) Simple constructor.

Method Summary

Modifier and Type	Method and Description
TopocentricFrame	getBaseFrame() Get the base frame associated with the station.
ParameterDriver	getClockDriftDriver() Get a driver allowing to change station clock drift (which is related to measurement date).
ParameterDriver	getClockOffsetDriver() Get a driver allowing to change station clock (which is related to measurement date).
StationDisplacement[]	getDisplacements() Get the displacement models.
ParameterDriver	getEastOffsetDriver() Get a driver allowing to change station position along East axis.
Frame	getEstimatedEarthFrame() Get the estimated Earth frame, including the estimated linear models for pole and prime meridian.
UT1Scale	getEstimatedUT1() Get the estimated UT1 scale, including the estimated linear models for prime meridian.
ParameterDriver	getNorthOffsetDriver() Get a driver allowing to change station position along North axis.
GeodeticPoint	getOffsetGeodeticPoint(AbsoluteDate date) Get the geodetic point at the center of the offset frame.
Transform	getOffsetToInertial(Frame inertial, AbsoluteDate clockDate) Get the transform between offset frame and inertial frame.
FieldTransform<Gradient>	getOffsetToInertial(Frame inertial, AbsoluteDate clockDate, int freeParameters, Map<String,Integer> indices) Get the transform between offset frame and inertial frame with derivatives.
FieldTransform<Gradient>	getOffsetToInertial(Frame inertial, FieldAbsoluteDate<Gradient> offsetCompensatedDate, int freeParameters, Map<String,Integer> indices) Get the transform between offset frame and inertial frame with derivatives.
ParameterDriver	getPolarDriftXDriver() Get a driver allowing to add a polar drift along X.
ParameterDriver	getPolarDriftYDriver() Get a driver allowing to add a polar drift along Y.
ParameterDriver	getPolarOffsetXDriver() Get a driver allowing to add a polar offset along X.
ParameterDriver	getPolarOffsetYDriver() Get a driver allowing to add a polar offset along Y.
ParameterDriver	getPrimeMeridianDriftDriver() Get a driver allowing to add a prime meridian rotation rate.
ParameterDriver	getPrimeMeridianOffsetDriver() Get a driver allowing to add a prime meridian rotation.
ParameterDriver	getZenithOffsetDriver() Get a driver allowing to change station position along Zenith axis.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Field Detail

OFFSET_SUFFIX

public static final String OFFSET_SUFFIX

Suffix for ground station position and clock offset parameters names.

See Also:

Constant Field Values

DRIFT_SUFFIX

public static final String DRIFT_SUFFIX

Suffix for ground clock drift parameters name.

See Also:

Constant Field Values

INTERMEDIATE_SUFFIX

public static final String INTERMEDIATE_SUFFIX

Suffix for ground station intermediate frame name.

See Also:

Constant Field Values

Constructor Detail

GroundStation

public GroundStation(TopocentricFrame baseFrame)

Build a ground station ignoring station displacements.

The initial values for the pole and prime meridian parametric linear models (getPrimeMeridianOffsetDriver(), getPrimeMeridianDriftDriver(), getPolarOffsetXDriver(), getPolarDriftXDriver(), getPolarOffsetXDriver(), getPolarDriftXDriver()) are set to 0. The initial values for the station offset model (getClockOffsetDriver(), getEastOffsetDriver(), getNorthOffsetDriver(), getZenithOffsetDriver()) are set to 0. This implies that as long as these values are not changed, the offset frame is the same as the base frame. As soon as some of these models are changed, the offset frame moves away from the base frame.

Parameters:

baseFrame - base frame associated with the station, without *any* parametric model (no station offset, no polar motion, no meridian shift)

See Also:

GroundStation(TopocentricFrame, EOPHistory, StationDisplacement...)

GroundStation

public GroundStation(TopocentricFrame baseFrame,
                     EOPHistory eopHistory,
                     StationDisplacement... displacements)

Simple constructor.

The initial values for the pole and prime meridian parametric linear models (getPrimeMeridianOffsetDriver(), getPrimeMeridianDriftDriver(), getPolarOffsetXDriver(), getPolarDriftXDriver(), getPolarOffsetXDriver(), getPolarDriftXDriver()) are set to 0. The initial values for the station offset model (getClockOffsetDriver(), getEastOffsetDriver(), getNorthOffsetDriver(), getZenithOffsetDriver(), getClockOffsetDriver()) are set to 0. This implies that as long as these values are not changed, the offset frame is the same as the base frame. As soon as some of these models are changed, the offset frame moves away from the base frame.

Parameters:

baseFrame - base frame associated with the station, without *any* parametric model (no station offset, no polar motion, no meridian shift)

eopHistory - EOP history associated with Earth frames

displacements - ground station displacement model (tides, ocean loading, atmospheric loading, thermal effects...)

Since:

9.1

Method Detail

getDisplacements

public StationDisplacement[] getDisplacements()

Get the displacement models.

Returns:

displacement models (empty if no model has been set up)

Since:

9.1

getClockOffsetDriver

public ParameterDriver getClockOffsetDriver()

Get a driver allowing to change station clock (which is related to measurement date).

Returns:

driver for station clock offset

Since:

9.3

getClockDriftDriver

public ParameterDriver getClockDriftDriver()

Get a driver allowing to change station clock drift (which is related to measurement date).

Returns:

driver for station clock drift

Since:

10.3

getEastOffsetDriver

public ParameterDriver getEastOffsetDriver()

Get a driver allowing to change station position along East axis.

Returns:

driver for station position offset along East axis

getNorthOffsetDriver

public ParameterDriver getNorthOffsetDriver()

Get a driver allowing to change station position along North axis.

Returns:

driver for station position offset along North axis

getZenithOffsetDriver

public ParameterDriver getZenithOffsetDriver()

Get a driver allowing to change station position along Zenith axis.

Returns:

driver for station position offset along Zenith axis

getPrimeMeridianOffsetDriver

public ParameterDriver getPrimeMeridianOffsetDriver()

Get a driver allowing to add a prime meridian rotation.

The parameter is an angle in radians. In order to convert this value to a DUT1 in seconds, the value must be divided by ave = 7.292115146706979e-5 (which is the nominal Angular Velocity of Earth from the TIRF model).

Returns:

driver for prime meridian rotation

getPrimeMeridianDriftDriver

public ParameterDriver getPrimeMeridianDriftDriver()

Get a driver allowing to add a prime meridian rotation rate.

The parameter is an angle rate in radians per second. In order to convert this value to a LOD in seconds, the value must be multiplied by -86400 and divided by ave = 7.292115146706979e-5 (which is the nominal Angular Velocity of Earth from the TIRF model).

Returns:

driver for prime meridian rotation rate

getPolarOffsetXDriver

public ParameterDriver getPolarOffsetXDriver()

Get a driver allowing to add a polar offset along X.

The parameter is an angle in radians

Returns:

driver for polar offset along X

getPolarDriftXDriver

public ParameterDriver getPolarDriftXDriver()

Get a driver allowing to add a polar drift along X.

The parameter is an angle rate in radians per second

Returns:

driver for polar drift along X

getPolarOffsetYDriver

public ParameterDriver getPolarOffsetYDriver()

Get a driver allowing to add a polar offset along Y.

The parameter is an angle in radians

Returns:

driver for polar offset along Y

getPolarDriftYDriver

public ParameterDriver getPolarDriftYDriver()

Get a driver allowing to add a polar drift along Y.

The parameter is an angle rate in radians per second

Returns:

driver for polar drift along Y

getBaseFrame

public TopocentricFrame getBaseFrame()

Get the base frame associated with the station.

The base frame corresponds to a null position offset, null polar motion, null meridian shift

Returns:

base frame associated with the station

getEstimatedEarthFrame

public Frame getEstimatedEarthFrame()

Get the estimated Earth frame, including the estimated linear models for pole and prime meridian.

This frame is bound to the driver for prime meridian offset, driver prime meridian drift, driver for polar offset along X, driver for polar drift along X, driver for polar offset along Y, driver for polar drift along Y, so its orientation changes when the setValue methods of the drivers are called.

Returns:

estimated Earth frame

Since:

9.1

getEstimatedUT1

public UT1Scale getEstimatedUT1()

Get the estimated UT1 scale, including the estimated linear models for prime meridian.

This time scale is bound to the driver for prime meridian offset, and driver prime meridian drift, so its offset from UTC changes when the setValue methods of the drivers are called.

Returns:

estimated Earth frame

Since:

9.1

getOffsetGeodeticPoint

public GeodeticPoint getOffsetGeodeticPoint(AbsoluteDate date)

Get the geodetic point at the center of the offset frame.

Parameters:

date - current date (may be null if displacements are ignored)

Returns:

geodetic point at the center of the offset frame

Since:

9.1

getOffsetToInertial

public Transform getOffsetToInertial(Frame inertial,
                                     AbsoluteDate clockDate)

Get the transform between offset frame and inertial frame.

The offset frame takes the current position offset, polar motion and the meridian shift into account. The frame returned is disconnected from later changes in the parameters. When the parameters managing these offsets are changed, the method must be called again to retrieve a new offset frame.

Parameters:

inertial - inertial frame to transform to

clockDate - date of the transform as read by the ground station clock (i.e. clock offset not compensated)

Returns:

transform between offset frame and inertial frame, at real measurement date (i.e. with clock, Earth and station offsets applied)

getOffsetToInertial

public FieldTransform<Gradient> getOffsetToInertial(Frame inertial,
                                                    AbsoluteDate clockDate,
                                                    int freeParameters,
                                                    Map<String,Integer> indices)

Get the transform between offset frame and inertial frame with derivatives.

As the East and North vectors are not well defined at pole, the derivatives of these two vectors diverge to infinity as we get closer to the pole. So this method should not be used for stations less than 0.0001 degree from either poles.

Parameters:

inertial - inertial frame to transform to

clockDate - date of the transform as read by the ground station clock (i.e. clock offset not compensated)

freeParameters - total number of free parameters in the gradient

indices - indices of the estimated parameters in derivatives computations

Returns:

transform between offset frame and inertial frame, at real measurement date (i.e. with clock, Earth and station offsets applied)

Since:

10.2

See Also:

getOffsetToInertial(Frame, FieldAbsoluteDate, int, Map)

getOffsetToInertial

public FieldTransform<Gradient> getOffsetToInertial(Frame inertial,
                                                    FieldAbsoluteDate<Gradient> offsetCompensatedDate,
                                                    int freeParameters,
                                                    Map<String,Integer> indices)

Get the transform between offset frame and inertial frame with derivatives.

As the East and North vectors are not well defined at pole, the derivatives of these two vectors diverge to infinity as we get closer to the pole. So this method should not be used for stations less than 0.0001 degree from either poles.

Parameters:

inertial - inertial frame to transform to

offsetCompensatedDate - date of the transform, clock offset and its derivatives already compensated

freeParameters - total number of free parameters in the gradient

indices - indices of the estimated parameters in derivatives computations

Returns:

transform between offset frame and inertial frame, at specified date

Since:

10.2