For quite a while, some of us have been using git to keep track of
FlightGear files.  Using git instead of CVS is like having a sports
car instead of a skateboard.

  Git is super-convenient for testing and for experimenting with
  things.  You can very cheaply start a new branch, play around on
  that branch, compare files against the corresponding files on other
  branches ... and then reset the branch (or throw it away entirely)
  if you decide you don't like where it has gone.

  Git implements a truly distributed development model.  Everything,
  including the "repository", is fully distributed; your copy of the
  history is provably equivalent to my copy of the history.

     This stands in contrast to CVS, which permits concurrent
     development, but not really distributed development, because
     distributors are at the mercy of the single centralized
     repository.  CVS is a Centralized Versioning System.

  Git also features the notion of committing a group of files all at
  once, which is a much more logical way to think about things.

      This is in contrast to the CVS notion of committing files one by
      one.

Another nice feature of git is called "gitweb".  It provides a web
interface that allows convenient point-and-click navigation of the
logs, commit messages, diffs, et cetera.  Pigeon has made a gitweb 
available at:
  http://pigeond.net/git/


If you want to go try this, the work required to get started will be
greatly lessened if you download the git repositories in their
already-packed form.  The FlightGear "data" tree is available via
the commands

  top=...whatever...
  mkdir $top/fgd
  cd $top/fgd
  time git-pull  http://www.av8n.com/repo/fgd/.git origin:origin
  ## 600 megabytes of network traffic, expands to 1.5 gigs on disk
  time git-pull  http://www.av8n.com/repo/fgd/.git sport:sport
  ## incrementally almost nothing
  git checkout sport
  git checkout -b myversion  ## or whatever you want to call it

What you have at this point in the "origin" branch is conceptually
equivalent to the current CVS version.  Furthermore, you also have
easy local access to every previous version of every file, immediately
available for your use if/when you want them.  This includes all log
messages.  Use git checkout origin git log to see what I mean.

Meanwhile, in the "sport" branch, you have all the modifications I've
made, including the ATIS/AWOS, much improved air-column physics,
gremlins, instrument status flags, and many others.  For a list of the
main features of sport model, see ./README.sport.model

You can also do
  git checkout sport
  git log
to see in great detail what is in that branch.

The same procedure used for the "data" tree works for the "source"
tree: 
  mkdir $top/fgs
  cd $top/fgs
  git-init
  time git-pull  http://www.av8n.com/repo/fgs/.git origin:origin
  ## less than a minute
  time git-pull  http://www.av8n.com/repo/fgs/.git sport:sport
  ## even less
  git branch    ## take a look
  git checkout sport
  git checkout -b myversion  ## or whatever you want to call it
  edit...as...desired
  time ./autogen.sh
  ./configure
  time make

And similarly for the "simgear" tree, in /repo/sg/.git:
  mkdir $top/sg
  ... and so forth ...

There is also an OSG version 2 tree in /repo/osg2/.git.
There is no sport branch in osg2;  the Sport Model uses
the plain old origin branch.

######################################

For more info on how to use git, see
  http://www.kernel.org/pub/software/scm/git/docs/tutorial.html
  http://git.or.cz/gitwiki
  http://git.or.cz/gitwiki/GitFaq

Notes: 

  1) Every so often, I import changes so that the "origin" branch
   exactly tracks the current CVS.  

  2) I then pull changes from the "origin" branch into the "sport"
   branch, so that it gets the new features also.  The idea is *not*
   to have a fork, where each branch has some features that the other 
   lacks.  The idea is for the Sport Model to be an extension (not a
   fork) of the CVS version.

   While sitting on the sport branch (or any other branch) you can
   do "git diff origin --" to see exactly how this branch differs
   From the origin.  (More generally:  I find git diff to be
   wonderfully useful.)

  3) A standard recommendation is that you not edit the origin branch
   or the sport branch; leave them to be updated by git-pull and only
   git-pull.  Start your own branch, and do your editing there.  (You
   can easily pull in updates from other branches whenever you want.)