File Overview
-------------

* winmain.cpp
  Windows front-end.  There's a lot of initialization code that should be
  moved to a module that's not platform-specific.

* simulation.cpp
  The heart of Celestia . . .  handles tracking an observer moving through
  the universe.

* render.cpp
  The Renderer class.  Everything on the screen is put there by an instance
  of Renderer.

* bigfix.cpp
  High precision (128-bit) fixed point numbers.

* univcoord.cpp
  UnivseralCoord class--a 3-vector with BigFix components.  Represents
  positions over a range of billions of light years to about
  millimeter resolution.

* observer.cpp
  This class is a package for position, orientation, and velocity.  The
  position of the observer is a UniversalCoord.

* octree.cpp
  Octree is a class used to determine which stars from are visible to an
  Observer

* stellarclass.cpp
* starname.cpp
* star.cpp
* stardb.cpp
  Everything to do with stars.  StarDatabase contains a list of Stars and a
  list of StarNames.

* constellation.cpp
  Just a bunch of static data giving the names and official abbreviations of
  the 88 recognized constellations.

* orbit.cpp
  The Orbit base class has a single method to compute the barycentric position
  of an object at a given Julian Date.  Currently, the only subclass of Orbit
  is EllipticalOrbit, which calculates the position of an object along an
  orbit specified by the standard six orbital elements.

* body.cpp
  A planet, moon, probe, etc.  Pretty much anything in space other than
  a star is a Body.  A PlanetarySystem is a list of bodies.

* solarsys.cpp
  SolarSystem and SolarSystemCatalog classes.

* mesh.cpp
* spheremesh.cpp
* 3dsmesh.cpp
* vertexlist.cpp
  These files are all related to internal geometry representation.
  Mesh is an abstract class from which SphereMesh and Mesh3DS are derived.
  VertexList is basically an easy to use wrapper for OpenGL 1.1 vertex arrays.
  Eventually, VertexList will be made a subclass of mesh (SimpleMesh) and
  Mesh3DS will be replaced by a more general class, CompositeMesh, which is
  just a container for multiple Meshes.

* surface.h
  An aggregation of surface properties that may be applied to a mesh.

* texture.cpp
  An OpenGL texture class.

* tokenizer.cpp
* parser.cpp
  The tokenizer and parser for Celestia text files (including the config file,
  the solar system catalogs, and Celestia procedural meshes)

* resmanager.cpp
* texmanager.cpp
* meshmanager.cpp
  Resource management.  Resource manager is an abstract class from which
  TextureManager and MeshManager are derived.  Right now, there isn't much
  in the way of actual management done, but having these classes around
  makes it much easier to implement a more sophisticated texture manager
  in the future.

* 3dschunk.h
* 3dsread.cpp
* 3dsmodel.cpp
  3DS mesh reading stuff.  Slurp a file and spits out a Mesh3DS.

* console.cpp
  GL text console class that supports both printf and C++ << style output.

* perlin.cpp
  Noise functions used for procedural geometry and textures.

* regcombine.cpp
  A few functions that make it easy to use nVidia's REGISTER_COMBINERS
  extension.

* color.cpp
  Simple RGBA color class.

* astro.cpp
  Astronomical conversions and a Date class for converting from dd/mm/yyyy
  to Julian date.

* vecgl.h
  A handful of template functions which make it easy to use types from
  Eigen with OpenGL

* glext.h
* glext.cpp
  GL extension declarations

* filetype.cpp
  A function for determining the type of a file based on its extension.

* dispmap.cpp
  Some silly code for applying displacement maps to SphereMeshes.

* texfont.cpp
  Mark J. Kilgard's texture font package

* buildstardb.cpp
  The program used to munge the HIPPARCOS data set into the star database.
  If you wish to munge your own database, you will need to download a copy
  of the HIPPARCOS database, it may be found at the URL:
  ftp://cdsarc.u-strasbg.fr/cats/I/239
  You will need the files hip_main.dat h_dm_com.dat hip_dm_o.da & tyc_main.dat


The Star Database
-----------------
The main star database is data/stars.dat.  This contains about 112,000 stars,
including most of the HIPPARCOS catalog, plus one addition: Sol, our
sun.  The file starnames.dat contains proper names and Bayer and Flamsteed
designations for about 1000 stars.  Every star in stars.dat has a unique
identifier called its catalog number, and the name entries are linked with
stars from the database via this number.

The readStars function in celestiacore.cpp is responsible for loading the star
database for Celestia.  Once initialized, the StarDatabase may be queried in
one of three ways:  by star index, by catalog number, or by star name.  The
star index is just the order of the star within the database, so lookup by
index is a constant time operation.  Looking up a star by catalog number
requires a search of the star database; since the database entries are sorted
by catalog number, this is a log N operation.  All three query types return
a pointer to a star from the database.


Stars
-----
Since there are so many stars in a star database, it's important that the
size of the Star class be kept to a minimum.  Thus, in order to avoid the
4 byte vtable overhead Star is not a derived class, even though it might
be somewhat useful to have a common base class for stars and planets.  All
stars have a unique catalog number, a position, a stellar class, and a
luminosity.  The radius, temperature, and color of a star are not stored,
but are instead derived from stellar class and luminosity.  The position
of a star is its cartesian ecliptical position in units of
light years.  The catalog number of a star is generally it's HD number.  In
cases where the star doesn't have an HD number, the lower 28 bits are the
HIPPARCOS catalog number and the high 4 bits are 0x1.


Celestia Overview
-----------------

The basic skeleton of Celestia looks like this:

StarDatabase* stardb = ReadStars("data/stars.dat", "data/starnames.dat");
SolarSystemCatalog* solarSystems = ReadSolarSystems("data/solarsys.ssc");
Simulation* sim = new Simulation();
sim->setStarDatabase(stardb);
sim->setTime(now);
Renderer renderer = new Renderer();
renderer->init();
for (;;)
{
    sim->update(tick);
    sim->render(*renderer);
}

The platform specific stuff to create a GL window and update it has been
omitted, as has any UI.


Tracking Visible Stars
----------------------
The VisibleStarSet class exists to limit the amount of computation spent
determining which stars from a StarDatabase are visible to an Observer.  The
fairly simple trick used to help alleviate the problem involves only checking a
portion of the database for visibility at each update.

UNIX
----
To develop under Unix, you will probably need some of the following packages:
autoconf, automake, and of course the usual array of c++ compilers/linkers.