File and Directory Structure

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This article explains the directory and file layout which Stellarium uses from a programmer's perspective, lays out the rationale behind it, and uses examples to illustrate the way things work.

Contents

Directory Structure

Files are broadly separated by the type of data. For StelModules which need many data files, there is one directory. e.g. StarMgr files are stored in the stars directory, LandscapeMgr files may be found in the landscapes directory.

There are also directories which are shared among modules and other parts of the program, for example the textures directory.

User and Installation directory separation

When Stellarium searches for data, texture and other files it looks in two separate locations:

  1. The User Data Directory, which stores per-user copies of any customised data files
  2. The Installation Data Directory, which is where the program executable, libraries and all data files which are distributed with the program are installed.

If a file exists in the User Data Directory, it will be used in preference to a file with the same name existing in the Installation Data Directory. This allows users to customise data files, textures and so on without modifying the originally installed files.

There are several reasons for doing this:

  1. On machines which multiple user accounts, the Installation Data Directory will likely not be writable by all users. Without allowing the User Data Directory files to over-ride Installation Data Directory files such users could not customise the program without doing an entirely separate installation.
  2. On multi-user systems, different users can customise Stellarium without affecting other users of the program.
  3. Users who modify files in the Installation Data Directory will likely have their work deleted or overwritten when they upgrade Stellarium. By keeping user-customised files separate from the installation, the upgrade procedure is easier to manage, and users have better security for their work.
  4. Users who mess up a customisation attempt need only remove the User Data Directory copy of a file to return to the original (working) copy.

Finding files with the StelFilMgr class

Whenever a file is needed in Stellarium, it should be located using the StelFileMgr class. This class will find the file in the first location in the search path. An instance of this class is maintained by the StelApp singleton.

StelFileMgr will throw exceptions when a problem is encountered, so it is important to always use "try ... catch ..." exception handling when using it.

For example. You are writing a class called Comet, and wish to search for a data file called "comets.dat" located in the data directory, you would go about it like this:

QString path;
try
{
        path = StelApp::getInstance().getFileMgr().findFile("data/comets.dat");
}
catch(std::runtime_error& e)
{
        qWarning() << "Could not locate file: data/comets.dat : " << e.what();
}

...

As you can see, the file is specified only by the partial path. This partial path is appended first to the User Data Directory. If, and only if the file is not found there, it is searched for in the Installation Data Directory. Thus if the user has a customised copy at: <User Data Directory>/data/comets.dat it will be used, else the version in the Installation Data Directory will be used.

Example: Star Catalogue Download Tool

Stellarium ships with the first four star catalogue files of nine files. The implementation of a catalogue downloading tool helps ease the task for users wanting the extra catalogues by automating the download and installation procedure.

The files which come with Stellarium are found by the partial paths:

stars/default/stars_0_0v0_1.cat
stars/default/stars_1_0v0_1.cat
stars/default/stars_2_0v0_1.cat
stars/default/stars_3_1v0_1.cat

Naturally, these files are to be located in the Installation Data Directory (because they ship with the installer).

The catalogue downloader tool runs within Stellarium. When it downloads extra star catalogue files, it should place them in the User Data Directory. After downloading all the catalogues, the paths to the various files should look like this:

<Installation Data Directory>/stars/default/stars_0_0v0_1.cat
<Installation Data Directory>/stars/default/stars_1_0v0_1.cat
<Installation Data Directory>/stars/default/stars_2_0v0_1.cat
<Installation Data Directory>/stars/default/stars_3_1v0_1.cat
<User Data Directory>/stars/default/stars_4_1v0_0.cat
<User Data Directory>/stars/default/stars_5_2v0_0.cat
<User Data Directory>/stars/default/stars_6_2v0_0.cat
<User Data Directory>/stars/default/stars_7_2v0_0.cat
<User Data Directory>/stars/default/stars_8_2v0_0.cat


It might be that someone makes a customised installer of Stellarium which includes all the star catalogues with the main installation - perhaps on a special edition DVD. In this case, all the files would be in the <Installation Data Directory>/stars/default directory. The downloader tool should be able to cope with this, not re-downloading files into the User Data Directory which already reside in the Installation Data Directory.

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