Understanding FlightGear Scenery

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If you want to develop scenery for FlightGear, great! FlightGear needs as much help as possible with modeling the world. This article is designed for someone who is interested in creating FlightGear scenery for the first time and this is meant to explain how FlightGear manages scenery and what quirks or nuances you need to know in order to best contribute.

How Scenery is Generated

There are three main types of data which make up FlightGear scenery - airports, objects and terrain.

All Airports and Terrain are generated using the TerraGear software. The vast majority of objects can be placed dynamically, using either the UFO aircraft model, or by finding the latitude and longitude of the object and placing it manually through text files.

All scenery which is included in the main FlightGear database should be derived from either license-free data or data which there is implicit permission to use. For instance, using USGS imagery, LANDSAT satellite imagery, or even Yahoo! Maps is okay for placing models or checking coordinates of airport runways. However, the FlightGear scenery project is copyright aware and typically does not accept objects or terrain created from copyrighted data, including, unfortunately, Google. (Yahoo! Maps has told OpenStreetMap deriving coordinates from their map data is not a copyright issue.) If you have a question about your source, do not hesitate to ask on the forum.

How Scenery is Stored

FlightGear manages scenery through a folder hierarchy representing square degrees for both Objects and Terrain. The purpose of separating scenery tiles by degree is to allow easy internet distribution and to provide boundaries for the generation of terrain, so polygons do not just go on for miles.

This means you need to know where your scenery project is in longitude and latitude. For instance, San Francisco's airport can be found under the folder w123n37.

The Basic Format

The /Scenery folder for FlightGear contains three subfolders - Airports, Objects and Terrain.

Airports

This folder contains various .xml files for the airports you have downloaded. You do not need to edit these!

If you are interested in contributing airport data, you will want to use TaxiDraw. Unfortunately TaxiDraw is not very robust at the moment, but it works. As of January 2010, FlightGear uses an older version of the X-Plane airport data. The kind people over at the Scenery Model Database accept updated airports in the X-Plane 8.10 format.

Because of the FlightGear feature which allows airports to undulate, or change elevation, all airports must be regenerated using TerraGear once TaxiDraw has been used.

Objects

Objects are possibly the easiest sceneries to create for FlightGear. All you need is to create an .ac model and place it using the ufo or manually using co-ordinates. You can also create an .xml file to create animations.

Objects are stored in a global database, the FlightGear Scenery Model Database. Once you have modeled your building, please make sure to send it into the database, as this is how your work gets distributed! Your work will be available to TerraSync users shortly after it is added.

Please note there is a difference between SHARED and STATIC objects. SHARED objects are objects which are included within the whole scenery, regardless of where you are. STATIC objects are specific objects, which appear a limited number of times (usually once) in the scenery. For instance, a house created to be auto-generated scenery would be a SHARED model, while the model of the tallest skyscraper in the country would be a STATIC model. SHARED models are typically to be avoided unless you know what you are doing, as they are loaded into memory when FlightGear starts up.

Terrain