.. _label_los_index:

====================
Line-of-sight module
====================

This module takes several :class:`~radis.spectrum.spectrum.Spectrum` objects as an input
and combines then along the line-of-sight (:func:`~radis.los.slabs.SerialSlabs`)
or at the same spatial position (:func:`~radis.los.slabs.MergeSlabs`), to reproduce
line-of-sight experiments

How to combine slabs?
=====================


Along the line-of-sight
-----------------------

Use the :func:`~radis.los.slabs.SerialSlabs` function::

    s1 = calc_spectrum(...)
    s2 = calc_spectrum(...)
    s3 = SerialSlabs(s1, s2)

You can also use the ``>`` operator. The previous line
is equivalent to::

    s3 = s1 > s2

.. minigallery:: radis.SerialSlabs


At the same spatial position
----------------------------

Use the :func:`~radis.los.slabs.MergeSlabs` function:

Merge two spectra calculated with different species (true only if broadening
coefficient dont change much)::

    from radis import calc_spectrum, MergeSlabs
    s1 = calc_spectrum(...)
    s2 = calc_spectrum(...)
    s3 = MergeSlabs(s1, s2)

You can also use the ``//`` operator. The previous line
is equivalent to::

    s3 = s1 // s2

.. minigallery:: radis.MergeSlabs

-----------------------------------------------------------------------

Practical Examples
==================

Below are some practical examples of the use of the Line-of-sight module:


Build a large spectrum
----------------------

If you want to calculate a spectrum on a very large spectral range which
cannot be handled in memory at once, you can calculate partial, non-overlapping
spectral ranges and use :func:`~radis.los.slabs.MergeSlabs` to combine them.
In that case, we tell :func:`~radis.los.slabs.MergeSlabs` to use the full
spectral range and that the partial spectra are transparent outside of their
definition range::

    from radis import load_spec, MergeSlabs
    spectra = []
    for f in ['spec1.spec', 'spec2.spec', ...]:  # precomputed spectra
        spectra.append(load_spec(f))
    s = MergeSlabs(*spectra, resample='full', out='transparent')
    s.plot()


Get the contribution of each slab along the LOS
-----------------------------------------------

Let's say you have a total line of sight::

    s_los = s1 > s2 > s3

If you want to get the contribution of ``s2`` to the line-of-sight emission,
you need to discard the emission of ``s3`` but take into account its absorption.
This is done using the :py:func:`~radis.spectrum.operations.PerfectAbsorber`
function, which returns a new Spectrum with all the emission features set to 0::

    from radis import PerfectAbsorber
    (s2 > PerfectAbsorber(s3)).plot('radiance_noslit')

And the contribution of ``s1`` would be::

    (s1 > PerfectAbsorber(s2>s3)).plot('radiance_noslit')