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__NOTOC__
== Introduction ==
=== Scope ===
The purpose of this chapter is to describe the current Patrius attitude legs.

An attitude leg is a time-bounded attitude law. Generalities on attitude laws can be found [ATT_ALW_Home here].

=== Javadoc ===
{| class="wikitable"
|-
! scope="col"| Library
! scope="col"| Javadoc
|-
|Patrius
|[{{JavaDoc4.10}}/fr/cnes/sirius/patrius/attitudes/package-summary.html Package fr.cnes.sirius.patrius.attitudes]
|-
|Patrius
|[{{JavaDoc4.10}}/fr/cnes/sirius/patrius/attitudes/package-summary.html Package fr.cnes.sirius.patrius.attitudes]
|}

=== Links ===

Orekit attitudes : [https://www.orekit.org/static/architecture/attitudes.html Orekit Attitudes architecture description ]

=== Useful Documents ===
None as of now.

=== Package Overview ===
The attitude leg <code>AttitudeLeg</code> interface inherits the <code>AttitudeProvider</code> interface.
Its place in the global Attitude design can be found [ATT_ALW_PkgOverview here].
It also inherits the general <code>Leg</code> interface presented below.

== Features Description ==

=== Generalities: the Leg and the LegsSequence interfaces ===
Attitude legs inherit the interface <code>AttitudeLeg</code>.
In addition to <code>AttitudeProvider</code> services, they inherit the methods of the <code>Leg</code> interface which means they are time-bounded attitude providers.

The <code>Leg</code> interface is a generic interface for time-bounded timestamped data. It has only one method <code>getTimeInterval()</code> (as well as method allowing to retrieve start and end of interval). This <code>Leg</code> interface allows to define an <code>AttitudeLeg</code>.

In order to define an attitude sequence <code>StrictAttitudeLegsSequence</code>, another generic interface is available: the <code>LegsSequence</code> interface. This interface defines a sequence of <code>Leg</code> and provides methods to manipulate a collection of timestamped legs similarly to the <code>Collection</code> interface (methods <code>first()</code>, <code>next()</code>, etc.).
A implementation of <code>LegsSequence</code> is available: <code>StrictLegsSequence</code>. This class handles a sequence of legs which are strictly ordered (not overlapping is allowed), legs are ordered by their starting date.
The sequence of attitude legs <code>StrictAttitudeLegsSequence</code> inherits the <code>StrictLegsSequence</code> by considering legs as <code>AttitudeLegs</code>.

'''Note:''' the <code>Leg</code>and <code>LegsSequence</code>interfaces are purely generic and therefore can be used for any other time-bounded data.

=== Available attitude leg ===
==== Attitude legs sequence ====
An attitude legs sequence is a container for several attitude legs, contiguous for their time intervals, in such a way that the attitude legs sequence can be processed like a single attitude leg by the propagator.

The attitude legs sequence is the equivalent of the [ATT_ALW_Home#HAttitudessequence Attitudes sequence], using attitude legs (<code>AttitudeLeg</code> instances) rather than attitude laws (<code>AttitudeLaw</code> instances).
The switching from one attitude leg to another is based on the time interval of validity of the two legs.

==== TabulatedAttitude ====
<code>TabulatedAttitude</code> is an implementation of <code>AttitudeLeg</code>. It represents a tabulated attitude leg.

In order to interpolate the attitude at a date, the user must specify a list of '''ordered''' attitudes, and can specify a number of points used by Hermite interpolation.
If not specified, the number of points used by Hermite interpolation is set to a default number (currently 2).
<syntaxhighlight lang="java">
final List<Attitude> attList = new ArrayList<Attitude>();
attList.add(attitude0);
attList.add(attitude1);
final int nbrInterpPoints = 2;
final TabulatedAttitude attLeg = new TabulatedAttitude(attList, nbrInterpPoints);
</syntaxhighlight>

It is possible to get the non-interpolated ordered attitudes :
<syntaxhighlight lang="java">
final List<Attitude> attitudes = attLeg.getAttitudes();
</syntaxhighlight>

Once the tabulated is defined, the computation can be performed on any orbital state using <code>getAttitude()</code> method:
<syntaxhighlight lang="java">
Attitude attitude = attLeg.getAttitude(orbit, date, FramesFactory.getEME2000());
</syntaxhighlight>

==== RelativeTabulatedAttitudeLeg ====
<code>RelativeTabulatedAttitudeLeg</code> is an implementation of <code>AttitudeLeg</code>. An instance of <code>RelativeTabulatedAttitudeLeg</code> can be created with a <code>List<Pair<Double, Rotation>></code> or with a <code>List<Pair<Double, AngularCoordinates>></code>. Each <code>Rotation</code> (or <code>AngularCoordinates</code>) is associated with a <code>double</code> representing its time ellapsed in seconds since the reference date. Here is an example of a creation of an instance of <code>RelativeTabulatedAttitudeLeg</code> :

<syntaxhighlight lang="java">
// date and frame
AbsoluteDate refDate = new AbsoluteDate(2008, 1, 1, TimeScalesFactory.getTAI());
Frame frame = FramesFactory.getGCRF();
double timeEllapsedSinceRefDate = 1.0;

// List of AR
List<Pair<Double, AngularCoordinates>> listAr = new ArrayList<Pair<Double, AngularCoordinates>>();
final AngularCoordinates ar = new AngularCoordinates(
new Rotation(false, 0.48, 0.64, 0.36, 0.48), Vector3D.PLUS_I, Vector3D.PLUS_J);
listAr.add(new Pair<Double, AngularCoordinates>(timeEllapsedSinceRefDate, ar));

// create RelativeTabulatedAttitudeLeg
final RelativeTabulatedAttitudeLeg relativeTabulatedAttitudeLeg =
new RelativeTabulatedAttitudeLeg(refDate, frame, listAr);
</syntaxhighlight>

== Getting Started ==
=== Building an attitude legs sequence ===

The attitude legs sequence was designed as a simple container, it performs only a few coherence checks on its inner attitude laws. Here's how an attitude sequence is built.

* An attitude legs sequence is created empty, associated to a single <code>PVCoordinatesProvider</code> instance.

* The sequence is mutable, attitude laws can be added to it one by one.

* Each attitude law is identified by a code.

* The sequence has a validity time interval, which is the grouping of the validity time intervals of all contained laws.

* The time interval of a newly added law must be contiguous to the grouped time interval of the already added laws. Otherwise an PatriusException is thrown.

* As soon as the sequence contains at least one law, methods of the <code>AttitudeLeg</code> interface can be called on the attitude sequence. The attitude sequence forwards the request to the appropriate attitude leg (according to the asking date), but replaces the <code>PVCoordinatesProvider</code> attribute of the call with the inner <code>PVCoordinatesProvider</code> instance.

=== AttitudeLawLeg and AttitudeLegsSequence : Code sample ===

<syntaxhighlight lang="java">
final BodyCenterPointing earthCenterAttitudeLaw = new BodyCenterPointing(itrf);
final AttitudeLeg law1 = new AttitudeLawLeg(earthCenterAttitudeLaw, date1, date2);
final AttitudeLeg law2 = ... ;
final AttitudeLeg law3 = ... ;

PVCoordinatesProvider pvProvider = new CartesianOrbit(pvCoordinates, gcrf, date1, mu);
final StrictAttitudeLegsSequence sequence = new StrictAttitudeLegsSequence(pvProvider);
sequence.add(law1);
sequence.add(law2);
sequence.add(law3);

// Call to getAttitude on the sequence
final Attitude attitude = sequence.getAttitude(pvProvider, date, itrf);
</syntaxhighlight>

== Contents ==
=== Interfaces ===
{| class="wikitable"
|-
! scope="col"| Interface
! scope="col"| Summary
! scope="col"| Javadoc
|-
|'''Leg'''
|This interface is a generic interface for any king of time-bounded data.
|[{{JavaDoc4.10}}/fr/cnes/sirius/patrius/utils/legs/Leg.html ...]
|-
|'''LegsSequence'''
|This interface is a generic interface for any sequence of legs.
|[{{JavaDoc4.10}}/fr/cnes/sirius/patrius/utils/legs/LegsSequence.html ...]
|-
|'''AttitudeLeg'''
|This interface extends the AttitudeProvider interface and adds the time interval of validity notion to the attitude laws.
|[{{JavaDoc4.10}}/fr/cnes/sirius/patrius/attitudes/AttitudeLeg.html ...]
|}

=== Classes ===
{| class="wikitable"
|-
! scope="col"| Class
! scope="col"| Summary
! scope="col"| Javadoc
|-
|'''StrictLegsSequence'''
|This class is a generic class for handling any sequence of legs.
|[{{JavaDoc4.10}}/fr/cnes/sirius/patrius/utils/legs/StrictLegsSequence.html ...]
|-
|'''AttitudeLawLeg'''
|Object representing an attitude law for spacecraft attitude field purposes.
|[{{JavaDoc4.10}}/fr/cnes/sirius/patrius/attitudes/AttitudeLawLeg.html ...]
|-
|'''TabulatedAttitude'''
|Object representing a tabulated attitude leg : the attitude at a date is interpolated from a list of known ones.
|[{{JavaDoc4.10}}/fr/cnes/sirius/patrius/attitudes/TabulatedAttitude.html ...]
|-
|'''StrictAttitudeLegsSequence'''
|Object representing a sequence of attitude legs.
|[{{JavaDoc4.10}}/fr/cnes/sirius/patrius/attitudes/StrictAttitudeLegsSequence.html ...]
|-
|'''RelativeTabulatedAttitudeLeg'''
|This class implements a tabulated attitude leg with relative dates.
|[{{JavaDoc4.10}}/fr/cnes/sirius/patrius/attitudes/RelativeTabulatedAttitudeLeg.html ...]
|}

[[Category:User_Manual_4.10_Attitude]]

User Manual 4.10 Attitude leg - Historique des versions

Admin : Page créée avec « __NOTOC__ == Introduction == === Scope === The purpose of this chapter is to describe the current Patrius attitude legs. An attitude leg is a time-bounded attitude law.... »

Admin : Page créée avec « NOTOC == Introduction == === Scope === The purpose of this chapter is to describe the current Patrius attitude legs. An attitude leg is a time-bounded attitude law.... »