.. _stateMerge:

:module-type:`Python` Module: stateMerge
========================================

Executive Summary
-----------------

This module combines attitude information from one spacecraft state message
with translational information from another spacecraft state message.  The
merged output is useful when a simulation has separate attitude and
center-of-mass state sources, but a downstream navigation module expects a
single ``SCStatesMsgPayload`` input.


Message Connection Descriptions
-------------------------------
The following diagram and table list the module input and output messages.

.. bsk-module-io:: StateMerge
    :caption: Module I/O Messages

    input attStateInMsg SCStatesMsgPayload
        Input spacecraft state message used as the attitude source.

    input transStateInMsg SCStatesMsgPayload
        Input spacecraft state message used as the translation source.

    output stateOutMsg SCStatesMsgPayload
        Output spacecraft state message containing merged attitude and translation fields.


Module Assumptions and Limitations
----------------------------------
The output attitude fields ``sigma_BN`` and ``omega_BN_B`` are copied from
``attStateInMsg``.  The output translation fields ``r_BN_N`` and ``v_BN_N`` are
populated from ``transStateInMsg`` fields ``r_CN_N`` and ``v_CN_N``.


User Guide
----------
The module is imported through the standard simulation package:

.. code-block:: python

    from Basilisk.simulation import stateMerge

    merge = stateMerge.StateMerge()
    merge.ModelTag = "stateMerge"

The two state input messages are connected in the usual Basilisk manner:

.. code-block:: python

    merge.attStateInMsg.subscribeTo(attStateMsg)
    merge.transStateInMsg.subscribeTo(transStateMsg)
    simpleNavObject.scStateInMsg.subscribeTo(merge.stateOutMsg)


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.. toctree::
   :maxdepth: 1
   :caption: Files:

.. automodule:: stateMerge
   :members:
   :show-inheritance: