Added an introduction and a list of features to the documentation.

docs/index.rst

@@ -1,6 +1,81 @@
 Introduction
 ============
 
+:mod:`optika` is a Python package for designing optical systems inspired by
+`Zemax <https://en.wikipedia.org/wiki/Zemax>`_.
+It allows the user to compute the spectral response and resolution of an
+arbitrary optical system and optimize it using :mod:`scipy.optimize`.
+The main design goals of :mod:`optika` are to
+
+* Use :mod:`astropy.units` to specify the parameters of an optical system.
+* Automatically compute the field of view and entrance pupil of a given optical
+  system.
+* Allow for :math:`n`-dimensional configurations of an optical system by allowing
+  its parameters to be array-like.
+* Compute uncertainties in the performance of an optical system using
+  the Monte-Carlo method.
+
+To satisfy the last two design goals, :mod:`optika` uses the
+purpose-built :mod:`named_arrays` package as a backend.
+:mod:`named_arrays` is an implementation of a
+`named tensor <https://nlp.seas.harvard.edu/NamedTensor>`_,
+which allows the user to name the axes in an :math:`n`-dimensional array.
+This makes specifying :math:`n`-dimensional configurations in :mod:`optika`
+easier since the user doesn't have to manually insert singleton dimensions
+to broadcast orthogonal configuration changes against each other.
+Furthermore, :mod:`named_arrays` provides an implementation of a 3D vector,
+:class:`named_arrays.Cartesian3dVectorArray`, which is convenient to use since
+many of the inputs and outputs of :mod:`optika` can be represented as 3D vectors.
+
+Features
+--------
+
+* Sequential raytrace modeling of an optical system
+* Stratified random sampling of input rays for faster convergence
+* Image simulation of a given scene using an optical system
+* Spherical, conical, and toroidal surface sag profiles
+* Circular, rectangular, and polygonal apertures
+* Support for mirrors and arbitrary multilayer coatings
+* Diffraction grating support
+
+  * Constant, polynomial and holographic ruling spacing
+  * Sinusoidal, square, rectangular, sawtooth, and triangular ruling profiles
+
+* CCD/CMOS sensor simulation
+
+  * Quantum efficiency
+  * Charge diffusion
+
+Some of the features :mod:`optika` is a work in progress, and many features
+
+Missing Features
+----------------
+
+* **Polarization**: Different polarization states are not propagated through the
+  system.
+* **Physical Optics**: Only geometric optics is supported right now, but adding
+  a Fourier optics propagator is a longstanding goal of the project.
+
+Differences from Zemax
+----------------------
+
+* The position and orientation of surfaces in :mod:`optika` are specified in
+  global coordinates instead of coordinates relative to the last surface.
+
+* The field of view is automatically calculated, there is no need to set the
+  extent of the field.
+
+* Diffraction grating rulings are now a parameter of an optical surface.
+  There is no need to change the type of surface to allow for different ruling
+  designs.
+
+
+
+API Reference
+=============
+
+An in-depth description of the interfaces in this package.
+
 .. autosummary::
     :toctree: _autosummary
     :template: module_custom.rst