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):

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 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	INTERMEDIATE_SUFFIX Suffix for ground station intermediate frame name.
static String	OFFSET_SUFFIX Suffix for ground station position offset parameter name.

Constructor Summary

Constructors

Constructor and Description
GroundStation(TopocentricFrame baseFrame) Simple constructor.

Method Summary

Modifier and Type	Method and Description
TopocentricFrame	getBaseFrame() Get the base frame associated with the station.
ParameterDriver	getEastOffsetDriver() Get a driver allowing to change station position along East axis.
ParameterDriver	getNorthOffsetDriver() Get a driver allowing to change station position along North axis.
GeodeticPoint	getOffsetGeodeticPoint() Get the geodetic point at the center of the offset frame.
Transform	getOffsetToInertial(Frame inertial, AbsoluteDate date) Get the transform between offset frame and inertial frame.
FieldTransform<DerivativeStructure>	getOffsetToInertial(Frame inertial, FieldAbsoluteDate<DerivativeStructure> date, DSFactory factory, 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 offset parameter 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)
              throws OrekitException

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 (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)

Throws:

OrekitException - if some frame transforms cannot be computed or if the ground station is not defined on a ellipsoid.

Method Detail

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

getOffsetGeodeticPoint

public GeodeticPoint getOffsetGeodeticPoint()
                                     throws OrekitException

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

Returns:

geodetic point at the center of the offset frame

Throws:

OrekitException - if frames transforms cannot be computed

getOffsetToInertial

public Transform getOffsetToInertial(Frame inertial,
                                     AbsoluteDate date)
                              throws OrekitException

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

date - date of the transform

Returns:

offset frame defining vectors

Throws:

OrekitException - if offset frame cannot be computed for current offset values

getOffsetToInertial

public FieldTransform<DerivativeStructure> getOffsetToInertial(Frame inertial,
                                                               FieldAbsoluteDate<DerivativeStructure> date,
                                                               DSFactory factory,
                                                               Map<String,Integer> indices)
                                                        throws OrekitException

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

As the East and North vector 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

date - date of the transform

factory - factory for the derivatives

indices - indices of the estimated parameters in derivatives computations

Returns:

offset frame defining vectors with derivatives

Throws:

OrekitException - if some frame transforms cannot be computed

Since:

9.0