The way scenery is created in FlightGear and how it can be modified can be confusing.
At a high level, there are two separate components of the FlightGear environment - the scenery itself and objects that site on top of the scenery.
Scenery
The scenery itself consisting of tiles representing the terrain, such as whether the the ground is a road, field, city or the sea. These tiles are built up from elevation data (SRTM-3), and data indicating the terrain itself (such as VMAP0). Airport layouts, such as runways and taxiways also fall into this category.
You cannot simply modify the terrain and view the results within FlightGear. Instead you must regenerate the terrain using a program called Terragear. This is sister-project to FlightGear. Instructions for running TerraGear can be found here:
http://wiki.flightgear.org/index.php?ti ... ar_Toolset
Objects
Objects sit on top of the scenery and include buildings, bridges, aerial masts, hangars and trees.
An object in the FG scenery context, is a 3-D model placed within the scenery. Some 3-D models are quite generic (such as a tree) and therefore can be used for multiple objects.
There is a huge database of objects and models available from the FlightGear Scenery Objects Database (FGSDB) at http://scenemodels.flightgear.org/.
Most 3-D models are .ac files. You can create a .ac file using a 3-D modelling program such as AC3D or Blender. It is also possible to convert models created using SketchUp using Blender, or the SketchUp_to .ac_export.rb converter available from http://vicmar.weebly.com/downloads.html.
Once you have created your model (or found one in the FGSDB), you can place it on the terrain using the ufo aircraft, and then submit it back to the FGSDB for use by others.
Creating new models and objects is an easy way to increase the realism of FG and contribute something back to the community.
FAQ
Q: How do I edit an airport layout?
A: You can use TaxiDraw to update the apt.dat file. However, this won't change the terrain within FG. For that you need to run Terragear to generate a new tile.
Q: Why don't we use data from google maps/earth?
A: Google's data license is incompatible with the GPL which FG uses, so it isn't possible to use it as the basis for scenery. However, it is a useful resource for working out where to place objects within the scenery and what they look like from above.
Q: Can I import Microsoft Flight Simulator Scenery (.bgl files)?
A: Short answer - no. The toolchain is too different. Sorry
Q: I want to create new models, but I don't understand Blender, or want to pay for AC3D. What can I do?
A: SketchUp is a bit easier to use than Blender. It is possible to import files from SketchUp into Blender and export them as .ac files, though you have to edit the textures afterwards. There are posts in this forum providing instructions.
Q: I created a new object and placed it using the UFO, then put the coordinates in the correct file in the scenery folder. However, now FG doesn't load and freezes when "loading scenery objects",
A: Check to make sure that you have no spaces in the name of the model you have created. The space in the name confuses FG. Rename the model
so there is no space in the name.
Q: How can I distribute my new object?
A: The best way to have it distributed is via Scenery Objects Database. (http://scenemodels.flightgear.org/) This is a global database of all the objects in the FlightGear world, and is linked into the scenery generation process. Having your model added to the database ensures that it will be available for future releases.
Q: I've found this really cool model/texture I want to use in a FG object. Anything I should be aware of?
A: The major issue we have is with licensing. If you want your object to go into the main scenery, or the Scenery Objects Database, then it must be released under the GNU GPL. If your model uses anything that wasn't directly created by yourself, e.g. if it was based or converted from another file, or uses textures you didn't create yourself, you need to make sure that any license you received with the original file is compatible with the GPL. If in doubt, assume that it isn't compatible.