Satellites Plugin for Stellatium
================================

INTRODUCTION
============

This feature has been requested so many times it's not funny.  Several
people have posted to the developer list saying they would like to have a
go and then the Yeti seem to get them and we never hear another thing.

Well, dagnammit, I thought I'd have a go.

I took the SDP4/SGP4 implementation from ktrack, adapting the use of
the library.

Projection is done from the azimuth/elevation data which the SDP4/SGP4
library handily produces.  Probably not the "right" way to do it, but 
it works and I am lazy.


TODO
====

+ When restoring default satellites.json, deleted satellites are
  somewhow not working right.  Something to do with deleteing a SatelliteP
  investigate and fix.
+ Fix data: trawl amsat site for updates and modify satellites.json
+ Do less frequent calls to the position calculation when a satellite
  is not near the observer
+ Rendering of the actual satellite, not just a hint/label
  - calculation of brightness, eclipse etc.
  - iridium flares?
+ Implement grouping so we can enable/disable groups, e.g.
  - gui widget with options to show/hide groups of satellites
+ gravity labels

Longer term:
+ proper 3d positions (when SolarSystem is refactored so we can see
  satellite cloud from the moon / other bodies.
+ trails (also after SolarSystem refactor)


BUILDING THE PLUGIN
===================

Please note, these instructions are only directly applicable to Linux.
Windows and OSX targets will probably require modification of the
CMakeLists.txt file.

0.  Install and build the SVN version of Stellarium as per the 
instructions on the Stellarium wiki:

  http://stellarium.org/wiki/index.php/Compilation_on_Linux

1.  Set the environment variable STELROOT to the root of the Stellarium
source tree.  The Stellarium build directory is expected to be:

  $STELROOT/builds/unix 

2.  Create a sub-directory builds/unix and change into that directory.

3.  Run:

  cmake ../.. 
  make
  make install

If all goes well, the relevant files should be built and copied to your 
~/.stellarium/modules directory.


ACKNOWLEGDEMENTS
================

SGP4/SDP4 implementation taken from KTrack codebase. There were some
minor modifications to prevent conflicts with #defines and enums from 
the core Stellarium code, but nothing significant.

The code which uses the SGP4/SDP4 library was copied more or less 
verbatim from KTrack up to the point of getting the alt/azi and other
data out.