.. _tutorial_vex_spice:

===============================
Tutorial to setup SPICE for VEX
===============================

Introduction
============

(To be writtern)


Preparation
===========

Install SPICE
-------------

Install ``SpiceyPy`` module, if having not done.

.. code-block:: sh

        pip install "git+https://github.com/AndrewAnnex/SpiceyPy.git"

If any problems below, considering updating the SpiceyPy.

.. code-block:: sh

        pip install "git+https://github.com/AndrewAnnex/SpiceyPy.git" -U

Download SPICE kernels
----------------------

Download the SPICE tree.  Easiest is to copy the tree from
``aurora.irf.se:/irf/spaghetti/venus/spice``.
Please change the destination directory name as your preference.

.. code-block:: sh

        mkdir -p /directory/for/vex/spice
        rsync -e ssh -abuv aurora.irf.se:/irf/spaghetti/venus/spice/kernels /directory/for/vex/spice/

.. note::

        The access to aurora is limited to IRF scientist.

Setup ``.irfpyrc``
------------------

Add the following entries to ``.irfpyrc`` at your home directory, or the current directory.

::

    [vexpvat]
    # Used in spice
    spiceroot = /directory/for/vex/spice/kernels/
    mk = /directory/for/vex/spice/vex.mk


Confirming installation
-----------------------

.. code-block:: python

    >>> import spiceypy as spice
    >>> spice.furnsh('/directory/for/vex/spice/kernels/lsk/NAIF0010.TLS')
    >>> spice.str2et('2005-11-09T03:33:33')     # Date of launch!
    184779277.18263602

.. code-block:: python

    >>> from irfpy.vexpvat import vexspice as vspice
    >>> vspice.init()
    >>> import datetime
    >>> vspice.get_position(datetime.datetime(2010, 1, 1, 0, 0, 0))
    [ 13651.59640042   1747.36719203 -59126.56129903]

SPICE in irfpy
==============


Import the :mod:`irfpy.vexpvat.vexspice` module.
It is a usual practice to import the module as ``vspice``.

.. code-block:: python

        >>> import irfpy.vexpvat.vexspice as vspice

Then, initialize the spice by using :func:`irfpy.vexpvat.vexspice.init` function.

.. code-block:: python

        >>> vspice.init()


To get the orbit
----------------

To get the spacecraft position, you can use :func:`irfpy.vexpvat.vexspice.get_position` function.

.. code-block:: python

        >>> import irfpy.vexpvat.vexspice as vspice
        >>> vspice.init()
        >>> import datetime
        >>> vspice.get_position(datetime.datetime(2010, 1, 1, 0, 0, 0))
        [ 13651.59640042   1747.36719203 -59126.56129903]

This is the VEX position in VSO frame measured from Venus.
You may specify the ``target``, ``origin`` and ``frame``.

.. code-block:: python

        >>> vspice.get_position(datetime.datetime(2010, 1, 1, 0, 0, 0), frame='J2000', origin='Sun', target='VEX')
        [  7964027.35161654, -98721990.65307485, -44986288.39865705]


To get the attitude
-------------------

(To be written)


SPICE functions
---------------

General spice functions (e.g. ``str2et``, ``mxv`` or whatever) can be used via `vspice.spice`, such as

.. code-block:: python

        >>> vspice.spice.mxv([[1, 2, 3], [1, 2, 4], [1, 3, 5]], [0, 0, 1])
        [ 3.,  4.,  5.]



Further learning of SPICE
=========================

(External link to be added)