Howto:Regional texturing

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The Flightgear terrain is created in a largely automated process from a large amount of geodata. The outcome may not necessarily always look like a region appears in reality. Regional texturing is one of the most powerful tools available to improve the visuals and get a result much closer to reality.

Background - terrain data structures

Tnternally, the terrain is a dense mesh of triangles which determine the elevation at each given point. However, the mesh also encodes what a patch of terrain is supposed to represent by assigning a so-called landclass to a triangle. Landclasses are a concept that is directly inherited from geo databases like CORINE. For instance, the database may tell that a certain patch of terrain is 'Shrubcover'. This information is stored with the terrain mesh.

Flightgear then uses it in-sim in several ways: First, the landclass of a triangle determines how it appears, i.e. what texture and/or effect are assigned. Second, it also determines FDM-relevant properties, for instance whether it will yield when you try to land on it (for instance water), whether you can roll across it, how bumpy rolling will be, and so on. The Advanced Weather system uses the landclass to determine the likelihood of convective cloud formation when the sun heats the terrain. Finally, also the distribution of random overlay objects (such as the density of lights at night or the number of trees or buildings appearing) is also determined by the landclass.

A separate layer for the terrain are static objects which are placed on definite positions onto the mesh by other means - for their placement, no landclass information is used and while they can be placed 'onto' the mesh automatically, they can also be placed to absolute altitudes.