Uses of Package
org.orekit.propagation

Packages that use org.orekit.propagation

Package	Description
org.orekit.attitudes	This package provides classes to represent simple attitudes.
org.orekit.control.indirect.adjoint	This package provides routines to model the adjoint dynamics as in the Pontryagin Maximum Principle, as used in indirect control.
org.orekit.control.indirect.shooting	This package provides routines to solve indirect optimal control within the frame of orbital mechanics, using shooting methods.
org.orekit.control.indirect.shooting.propagation	This package provides classes relative to the propagation part of indirect shooting.
org.orekit.estimation.leastsquares	The leastsquares package provides an implementation of a batch least squares estimator engine to perform an orbit determination.
org.orekit.estimation.measurements	The measurements package defines everything that is related to orbit determination measurements.
org.orekit.estimation.measurements.filtering	This package provides measurement pre-processing filters.
org.orekit.estimation.measurements.generation	This package provides Orbit Determination measurements generation.
org.orekit.estimation.measurements.gnss	This package provides methods to handle GNSS measurements.
org.orekit.estimation.measurements.modifiers	This package provides measurement modifier.
org.orekit.estimation.sequential	The sequential package provides an implementation of a Kalman Filter engine to perform an orbit determination.
org.orekit.files.ccsds.ndm.adm.aem	This package contains class managing CCSDS Attitude Ephemeris Message.
org.orekit.files.ccsds.ndm.odm.ocm	This package contains class managing CCSDS Orbit Comprehensive Message.
org.orekit.files.ccsds.ndm.odm.oem	This package contains class managing CCSDS Orbit Ephemeris Message.
org.orekit.files.ccsds.ndm.odm.omm	This package contains class managing CCSDS Orbit Mean-Elements Message.
org.orekit.files.ccsds.ndm.odm.opm	This package contains class managing CCSDS Orbit Parameter Message.
org.orekit.files.general	This package provides interfaces for orbit file representations and corresponding parsers.
org.orekit.files.ilrs	This package provides parsers for laser ranging data stored in CDR and CPF formats.
org.orekit.files.sp3	This package provides a parser for orbit data stored in SP3 format.
org.orekit.forces	This package provides the interface for force models that will be used by the NumericalPropagator, as well as some classical spacecraft models for surface forces (spherical, box and solar array ...).
org.orekit.forces.drag	This package provides all drag-related forces.
org.orekit.forces.empirical	This package provides empirical forces.
org.orekit.forces.gravity	This package provides all gravity-related forces.
org.orekit.forces.inertia	This package provides inertial force model.
org.orekit.forces.maneuvers	This package provides models of simple maneuvers.
org.orekit.forces.maneuvers.jacobians	Generators for columns of Jacobian matrices related to maneuver parameters.
org.orekit.forces.maneuvers.propulsion	This package provides propulsion models intended to be used with class Maneuver.
org.orekit.forces.maneuvers.trigger	This package provides maneuver triggers' models intended to be used with class Maneuver.
org.orekit.forces.radiation	This package provides all radiation pressure related forces.
org.orekit.gnss	This package provides classes related to GNSS applications.
org.orekit.models.earth.ionosphere	This package provides models that simulate the impact of the ionosphere.
org.orekit.orbits	This package provides classes to represent orbits.
org.orekit.propagation	Propagation
org.orekit.propagation.analytical	Top level package for analytical propagators.
org.orekit.propagation.analytical.gnss	This package provides classes to propagate GNSS orbits.
org.orekit.propagation.analytical.intelsat	This package provides classes to propagate Intelsat's 11 elements.
org.orekit.propagation.analytical.tle	This package provides classes to read and extrapolate tle's.
org.orekit.propagation.analytical.tle.generation	This package provides classes related to TLE generation.
org.orekit.propagation.conversion	This package provides tools to convert a given propagator or a set of SpacecraftState into another propagator.
org.orekit.propagation.events	This package provides interfaces and classes dealing with events occurring during propagation.
org.orekit.propagation.events.handlers	This package provides an interface and classes dealing with events occurrence only.
org.orekit.propagation.events.intervals	This package provides built-in implementations of AdaptableInterval.
org.orekit.propagation.integration	Utilities for integration-based propagators (both numerical and semi-analytical).
org.orekit.propagation.numerical	Top level package for numerical propagators.
org.orekit.propagation.numerical.cr3bp	Top level package for CR3BP Models used with a numerical propagator.
org.orekit.propagation.sampling	This package provides interfaces and classes dealing with step handling during propagation.
org.orekit.propagation.semianalytical.dsst	This package provides an implementation of the Draper Semi-analytical Satellite Theory (DSST).
org.orekit.propagation.semianalytical.dsst.forces	This package provides force models for Draper Semi-analytical Satellite Theory (DSST).
org.orekit.ssa.collision.shorttermencounter.probability.twod	Package specific to calculus assuming a 2D short-term encounter model.
org.orekit.utils	This package provides useful objects.

Classes in org.orekit.propagation used by org.orekit.attitudes

Class	Description
SpacecraftState	This class is the representation of a complete state holding orbit, attitude and mass information at a given date, meant primarily for propagation.

Classes in org.orekit.propagation used by org.orekit.control.indirect.adjoint

Class	Description
FieldSpacecraftState	This class is the representation of a complete state holding orbit, attitude and mass information at a given date, meant primarily for propagation.
SpacecraftState	This class is the representation of a complete state holding orbit, attitude and mass information at a given date, meant primarily for propagation.

Classes in org.orekit.propagation used by org.orekit.control.indirect.shooting

Class	Description
FieldSpacecraftState	This class is the representation of a complete state holding orbit, attitude and mass information at a given date, meant primarily for propagation.
SpacecraftState	This class is the representation of a complete state holding orbit, attitude and mass information at a given date, meant primarily for propagation.

Classes in org.orekit.propagation used by org.orekit.control.indirect.shooting.propagation

Class	Description
ToleranceProvider	Interface to define integration tolerances for adaptive schemes (like the embedded Runge-Kutta ones) propagating the position-velocity vector (or an equivalent set of coordinates) and the mass, for a total of 7 primary dependent variables (in that order).

Classes in org.orekit.propagation used by org.orekit.estimation.leastsquares

Class	Description
MatricesHarvester	Interface for extracting State Transition Matrices and Jacobians matrices from spacecraft state.
PropagationType	Enumerate to define the propagation type used by the propagator.
Propagator	This interface provides a way to propagate an orbit at any time.

Classes in org.orekit.propagation used by org.orekit.estimation.measurements

Class	Description
SpacecraftState	This class is the representation of a complete state holding orbit, attitude and mass information at a given date, meant primarily for propagation.

Classes in org.orekit.propagation used by org.orekit.estimation.measurements.filtering

Class	Description
SpacecraftState	This class is the representation of a complete state holding orbit, attitude and mass information at a given date, meant primarily for propagation.

Classes in org.orekit.propagation used by org.orekit.estimation.measurements.generation

Class	Description
Propagator	This interface provides a way to propagate an orbit at any time.
SpacecraftState	This class is the representation of a complete state holding orbit, attitude and mass information at a given date, meant primarily for propagation.

Classes in org.orekit.propagation used by org.orekit.estimation.measurements.gnss

Class	Description
SpacecraftState	This class is the representation of a complete state holding orbit, attitude and mass information at a given date, meant primarily for propagation.

Classes in org.orekit.propagation used by org.orekit.estimation.measurements.modifiers

Class	Description
FieldSpacecraftState	This class is the representation of a complete state holding orbit, attitude and mass information at a given date, meant primarily for propagation.
SpacecraftState	This class is the representation of a complete state holding orbit, attitude and mass information at a given date, meant primarily for propagation.

Classes in org.orekit.propagation used by org.orekit.estimation.sequential

Class	Description
Propagator	This interface provides a way to propagate an orbit at any time.
SpacecraftState	This class is the representation of a complete state holding orbit, attitude and mass information at a given date, meant primarily for propagation.

Classes in org.orekit.propagation used by org.orekit.files.ccsds.ndm.adm.aem

Class	Description
SpacecraftState	This class is the representation of a complete state holding orbit, attitude and mass information at a given date, meant primarily for propagation.

Classes in org.orekit.propagation used by org.orekit.files.ccsds.ndm.odm.ocm

Class	Description
SpacecraftState	This class is the representation of a complete state holding orbit, attitude and mass information at a given date, meant primarily for propagation.

Classes in org.orekit.propagation used by org.orekit.files.ccsds.ndm.odm.oem

Class	Description
SpacecraftState	This class is the representation of a complete state holding orbit, attitude and mass information at a given date, meant primarily for propagation.

Classes in org.orekit.propagation used by org.orekit.files.ccsds.ndm.odm.omm

Class	Description
SpacecraftState	This class is the representation of a complete state holding orbit, attitude and mass information at a given date, meant primarily for propagation.

Classes in org.orekit.propagation used by org.orekit.files.ccsds.ndm.odm.opm

Class	Description
SpacecraftState	This class is the representation of a complete state holding orbit, attitude and mass information at a given date, meant primarily for propagation.

Classes in org.orekit.propagation used by org.orekit.files.general

Class	Description
AbstractPropagator	Common handling of Propagator methods for analytical propagators.
BoundedPropagator	This interface is intended for ephemerides valid only during a time range.
Propagator	This interface provides a way to propagate an orbit at any time.
SpacecraftState	This class is the representation of a complete state holding orbit, attitude and mass information at a given date, meant primarily for propagation.

Classes in org.orekit.propagation used by org.orekit.files.ilrs

Class	Description
BoundedPropagator	This interface is intended for ephemerides valid only during a time range.
SpacecraftState	This class is the representation of a complete state holding orbit, attitude and mass information at a given date, meant primarily for propagation.

Classes in org.orekit.propagation used by org.orekit.files.sp3

Class	Description
BoundedPropagator	This interface is intended for ephemerides valid only during a time range.

Classes in org.orekit.propagation used by org.orekit.forces

Class	Description
FieldSpacecraftState	This class is the representation of a complete state holding orbit, attitude and mass information at a given date, meant primarily for propagation.
SpacecraftState	This class is the representation of a complete state holding orbit, attitude and mass information at a given date, meant primarily for propagation.

Classes in org.orekit.propagation used by org.orekit.forces.drag

Class	Description
FieldSpacecraftState	This class is the representation of a complete state holding orbit, attitude and mass information at a given date, meant primarily for propagation.
SpacecraftState	This class is the representation of a complete state holding orbit, attitude and mass information at a given date, meant primarily for propagation.

Classes in org.orekit.propagation used by org.orekit.forces.empirical

Class	Description
FieldSpacecraftState	This class is the representation of a complete state holding orbit, attitude and mass information at a given date, meant primarily for propagation.
SpacecraftState	This class is the representation of a complete state holding orbit, attitude and mass information at a given date, meant primarily for propagation.

Classes in org.orekit.propagation used by org.orekit.forces.gravity

Class	Description
FieldSpacecraftState	This class is the representation of a complete state holding orbit, attitude and mass information at a given date, meant primarily for propagation.
SpacecraftState	This class is the representation of a complete state holding orbit, attitude and mass information at a given date, meant primarily for propagation.

Classes in org.orekit.propagation used by org.orekit.forces.inertia

Class	Description
FieldSpacecraftState	This class is the representation of a complete state holding orbit, attitude and mass information at a given date, meant primarily for propagation.
SpacecraftState	This class is the representation of a complete state holding orbit, attitude and mass information at a given date, meant primarily for propagation.

Classes in org.orekit.propagation used by org.orekit.forces.maneuvers

Class	Description
FieldSpacecraftState	This class is the representation of a complete state holding orbit, attitude and mass information at a given date, meant primarily for propagation.
SpacecraftState	This class is the representation of a complete state holding orbit, attitude and mass information at a given date, meant primarily for propagation.

Classes in org.orekit.propagation used by org.orekit.forces.maneuvers.jacobians

Class	Description
AdditionalStateProvider	This interface allows to modify SpacecraftState and set up additional state data.
SpacecraftState	This class is the representation of a complete state holding orbit, attitude and mass information at a given date, meant primarily for propagation.

Classes in org.orekit.propagation used by org.orekit.forces.maneuvers.propulsion

Class	Description
FieldSpacecraftState	This class is the representation of a complete state holding orbit, attitude and mass information at a given date, meant primarily for propagation.
SpacecraftState	This class is the representation of a complete state holding orbit, attitude and mass information at a given date, meant primarily for propagation.

Classes in org.orekit.propagation used by org.orekit.forces.maneuvers.trigger

Class	Description
FieldSpacecraftState	This class is the representation of a complete state holding orbit, attitude and mass information at a given date, meant primarily for propagation.
SpacecraftState	This class is the representation of a complete state holding orbit, attitude and mass information at a given date, meant primarily for propagation.

Classes in org.orekit.propagation used by org.orekit.forces.radiation

Class	Description
FieldSpacecraftState	This class is the representation of a complete state holding orbit, attitude and mass information at a given date, meant primarily for propagation.
SpacecraftState	This class is the representation of a complete state holding orbit, attitude and mass information at a given date, meant primarily for propagation.

Classes in org.orekit.propagation used by org.orekit.gnss

Class	Description
Propagator	This interface provides a way to propagate an orbit at any time.

Classes in org.orekit.propagation used by org.orekit.models.earth.ionosphere

Class	Description
FieldSpacecraftState	This class is the representation of a complete state holding orbit, attitude and mass information at a given date, meant primarily for propagation.
SpacecraftState	This class is the representation of a complete state holding orbit, attitude and mass information at a given date, meant primarily for propagation.

Classes in org.orekit.propagation used by org.orekit.orbits

Class	Description
Propagator	This interface provides a way to propagate an orbit at any time.
SpacecraftState	This class is the representation of a complete state holding orbit, attitude and mass information at a given date, meant primarily for propagation.

Classes in org.orekit.propagation used by org.orekit.propagation

Class	Description
AbstractMatricesHarvester	Base harvester between two-dimensional Jacobian matrices and one-dimensional additional state arrays.
AbstractStateCovarianceInterpolator	Abstract class for orbit and state covariance interpolator.
AdditionalStateProvider	This interface allows to modify SpacecraftState and set up additional state data.
BoundedPropagator	This interface is intended for ephemerides valid only during a time range.
CartesianToleranceProvider	Interface to define integration tolerances for adaptive schemes (like the embedded Runge-Kutta ones) propagating the position-velocity vector and the mass, for a total of 7 primary dependent variables (in that order).
EphemerisGenerator	Generator for ephemerides.
FieldAdditionalStateProvider	This interface allows to modify FieldSpacecraftState and set up additional state data.
FieldBoundedPropagator	This interface is intended for ephemerides valid only during a time range.
FieldEphemerisGenerator	Generator for ephemerides.
FieldPropagator	This interface provides a way to propagate an orbit at any time.
FieldSpacecraftState	This class is the representation of a complete state holding orbit, attitude and mass information at a given date, meant primarily for propagation.
FieldStateCovariance	This class is the representation of a covariance matrix at a given date.
MatricesHarvester	Interface for extracting State Transition Matrices and Jacobians matrices from spacecraft state.
PropagationType	Enumerate to define the propagation type used by the propagator.
Propagator	This interface provides a way to propagate an orbit at any time.
SpacecraftState	This class is the representation of a complete state holding orbit, attitude and mass information at a given date, meant primarily for propagation.
StateCovariance	This class is the representation of a covariance matrix at a given date.
ToleranceProvider	Interface to define integration tolerances for adaptive schemes (like the embedded Runge-Kutta ones) propagating the position-velocity vector (or an equivalent set of coordinates) and the mass, for a total of 7 primary dependent variables (in that order).

Classes in org.orekit.propagation used by org.orekit.propagation.analytical

Class	Description
AbstractMatricesHarvester	Base harvester between two-dimensional Jacobian matrices and one-dimensional additional state arrays.
AbstractPropagator	Common handling of Propagator methods for analytical propagators.
AdditionalStateProvider	This interface allows to modify SpacecraftState and set up additional state data.
BoundedPropagator	This interface is intended for ephemerides valid only during a time range.
EphemerisGenerator	Generator for ephemerides.
FieldAbstractPropagator	Common handling of Propagator methods for analytical propagators.
FieldEphemerisGenerator	Generator for ephemerides.
FieldPropagator	This interface provides a way to propagate an orbit at any time.
FieldSpacecraftState	This class is the representation of a complete state holding orbit, attitude and mass information at a given date, meant primarily for propagation.
MatricesHarvester	Interface for extracting State Transition Matrices and Jacobians matrices from spacecraft state.
PropagationType	Enumerate to define the propagation type used by the propagator.
Propagator	This interface provides a way to propagate an orbit at any time.
SpacecraftState	This class is the representation of a complete state holding orbit, attitude and mass information at a given date, meant primarily for propagation.
StateCovariance	This class is the representation of a covariance matrix at a given date.

Classes in org.orekit.propagation used by org.orekit.propagation.analytical.gnss

Class	Description
AbstractPropagator	Common handling of Propagator methods for analytical propagators.
AdditionalStateProvider	This interface allows to modify SpacecraftState and set up additional state data.
Propagator	This interface provides a way to propagate an orbit at any time.
SpacecraftState	This class is the representation of a complete state holding orbit, attitude and mass information at a given date, meant primarily for propagation.

Classes in org.orekit.propagation used by org.orekit.propagation.analytical.intelsat

Class	Description
AbstractPropagator	Common handling of Propagator methods for analytical propagators.
FieldAbstractPropagator	Common handling of Propagator methods for analytical propagators.
FieldPropagator	This interface provides a way to propagate an orbit at any time.
FieldSpacecraftState	This class is the representation of a complete state holding orbit, attitude and mass information at a given date, meant primarily for propagation.
Propagator	This interface provides a way to propagate an orbit at any time.
SpacecraftState	This class is the representation of a complete state holding orbit, attitude and mass information at a given date, meant primarily for propagation.

Classes in org.orekit.propagation used by org.orekit.propagation.analytical.tle

Class	Description
AbstractMatricesHarvester	Base harvester between two-dimensional Jacobian matrices and one-dimensional additional state arrays.
AbstractPropagator	Common handling of Propagator methods for analytical propagators.
FieldAbstractPropagator	Common handling of Propagator methods for analytical propagators.
FieldPropagator	This interface provides a way to propagate an orbit at any time.
FieldSpacecraftState	This class is the representation of a complete state holding orbit, attitude and mass information at a given date, meant primarily for propagation.
Propagator	This interface provides a way to propagate an orbit at any time.
SpacecraftState	This class is the representation of a complete state holding orbit, attitude and mass information at a given date, meant primarily for propagation.

Classes in org.orekit.propagation used by org.orekit.propagation.analytical.tle.generation

Class	Description
FieldSpacecraftState	This class is the representation of a complete state holding orbit, attitude and mass information at a given date, meant primarily for propagation.
SpacecraftState	This class is the representation of a complete state holding orbit, attitude and mass information at a given date, meant primarily for propagation.

Classes in org.orekit.propagation used by org.orekit.propagation.conversion

Class	Description
PropagationType	Enumerate to define the propagation type used by the propagator.
Propagator	This interface provides a way to propagate an orbit at any time.
SpacecraftState	This class is the representation of a complete state holding orbit, attitude and mass information at a given date, meant primarily for propagation.
ToleranceProvider	Interface to define integration tolerances for adaptive schemes (like the embedded Runge-Kutta ones) propagating the position-velocity vector (or an equivalent set of coordinates) and the mass, for a total of 7 primary dependent variables (in that order).

Classes in org.orekit.propagation used by org.orekit.propagation.events

Class	Description
FieldSpacecraftState	This class is the representation of a complete state holding orbit, attitude and mass information at a given date, meant primarily for propagation.
SpacecraftState	This class is the representation of a complete state holding orbit, attitude and mass information at a given date, meant primarily for propagation.

Classes in org.orekit.propagation used by org.orekit.propagation.events.handlers

Class	Description
FieldSpacecraftState	This class is the representation of a complete state holding orbit, attitude and mass information at a given date, meant primarily for propagation.
SpacecraftState	This class is the representation of a complete state holding orbit, attitude and mass information at a given date, meant primarily for propagation.

Classes in org.orekit.propagation used by org.orekit.propagation.events.intervals

Class	Description
FieldSpacecraftState	This class is the representation of a complete state holding orbit, attitude and mass information at a given date, meant primarily for propagation.
SpacecraftState	This class is the representation of a complete state holding orbit, attitude and mass information at a given date, meant primarily for propagation.

Classes in org.orekit.propagation used by org.orekit.propagation.integration

Class	Description
AbstractPropagator	Common handling of Propagator methods for analytical propagators.
AdditionalStateProvider	This interface allows to modify SpacecraftState and set up additional state data.
BoundedPropagator	This interface is intended for ephemerides valid only during a time range.
EphemerisGenerator	Generator for ephemerides.
FieldAbstractPropagator	Common handling of Propagator methods for analytical propagators.
FieldAdditionalStateProvider	This interface allows to modify FieldSpacecraftState and set up additional state data.
FieldBoundedPropagator	This interface is intended for ephemerides valid only during a time range.
FieldEphemerisGenerator	Generator for ephemerides.
FieldPropagator	This interface provides a way to propagate an orbit at any time.
FieldSpacecraftState	This class is the representation of a complete state holding orbit, attitude and mass information at a given date, meant primarily for propagation.
PropagationType	Enumerate to define the propagation type used by the propagator.
Propagator	This interface provides a way to propagate an orbit at any time.
SpacecraftState	This class is the representation of a complete state holding orbit, attitude and mass information at a given date, meant primarily for propagation.

Classes in org.orekit.propagation used by org.orekit.propagation.numerical

Class	Description
AbstractMatricesHarvester	Base harvester between two-dimensional Jacobian matrices and one-dimensional additional state arrays.
AbstractPropagator	Common handling of Propagator methods for analytical propagators.
FieldAbstractPropagator	Common handling of Propagator methods for analytical propagators.
FieldPropagator	This interface provides a way to propagate an orbit at any time.
FieldSpacecraftState	This class is the representation of a complete state holding orbit, attitude and mass information at a given date, meant primarily for propagation.
Propagator	This interface provides a way to propagate an orbit at any time.
SpacecraftState	This class is the representation of a complete state holding orbit, attitude and mass information at a given date, meant primarily for propagation.

Classes in org.orekit.propagation used by org.orekit.propagation.numerical.cr3bp

Class	Description
FieldSpacecraftState	This class is the representation of a complete state holding orbit, attitude and mass information at a given date, meant primarily for propagation.
SpacecraftState	This class is the representation of a complete state holding orbit, attitude and mass information at a given date, meant primarily for propagation.

Classes in org.orekit.propagation used by org.orekit.propagation.sampling

Class	Description
FieldSpacecraftState	This class is the representation of a complete state holding orbit, attitude and mass information at a given date, meant primarily for propagation.
SpacecraftState	This class is the representation of a complete state holding orbit, attitude and mass information at a given date, meant primarily for propagation.

Classes in org.orekit.propagation used by org.orekit.propagation.semianalytical.dsst

Class	Description
AbstractMatricesHarvester	Base harvester between two-dimensional Jacobian matrices and one-dimensional additional state arrays.
AbstractPropagator	Common handling of Propagator methods for analytical propagators.
FieldAbstractPropagator	Common handling of Propagator methods for analytical propagators.
FieldPropagator	This interface provides a way to propagate an orbit at any time.
FieldSpacecraftState	This class is the representation of a complete state holding orbit, attitude and mass information at a given date, meant primarily for propagation.
MatricesHarvester	Interface for extracting State Transition Matrices and Jacobians matrices from spacecraft state.
PropagationType	Enumerate to define the propagation type used by the propagator.
Propagator	This interface provides a way to propagate an orbit at any time.
SpacecraftState	This class is the representation of a complete state holding orbit, attitude and mass information at a given date, meant primarily for propagation.

Classes in org.orekit.propagation used by org.orekit.propagation.semianalytical.dsst.forces

Class	Description
FieldSpacecraftState	This class is the representation of a complete state holding orbit, attitude and mass information at a given date, meant primarily for propagation.
PropagationType	Enumerate to define the propagation type used by the propagator.
SpacecraftState	This class is the representation of a complete state holding orbit, attitude and mass information at a given date, meant primarily for propagation.

Classes in org.orekit.propagation used by org.orekit.ssa.collision.shorttermencounter.probability.twod

Class	Description
FieldStateCovariance	This class is the representation of a covariance matrix at a given date.
StateCovariance	This class is the representation of a covariance matrix at a given date.

Classes in org.orekit.propagation used by org.orekit.utils

Class	Description
FieldSpacecraftState	This class is the representation of a complete state holding orbit, attitude and mass information at a given date, meant primarily for propagation.
FieldStateCovariance	This class is the representation of a covariance matrix at a given date.
SpacecraftState	This class is the representation of a complete state holding orbit, attitude and mass information at a given date, meant primarily for propagation.
StateCovariance	This class is the representation of a covariance matrix at a given date.