Archived from groups: alt.games.microsoft.flight-sim (
More info?)
Best description I have ever read. Many thanks for your efforts, Scott.
Arthur
"scott s." <75270_3703a@csi.xcom> wrote in message
news:Xns96377970FA702752703703acsicom@207.217.125.201...
> "Colin Bear" <colin(nospam)bear@btinternet.com> wrote in news:d3iep6$n36
> $1@titan.btinternet.com:
>
>> Hello all...
>>
>> First of all can someone define what land class scenery is?
>>
>
> Landclass is based on the geography concept that it is possible
> to characterize the earth surface by vegetation, soil, and
> built environment variations. This concept is useful to
> geographers, biologists, etc.
>
> For flight sim, there is the concept that earth surface has
> a visual appearance from the air that corresponds to the
> idea of land class. That is, it is possible to define types
> of land cover that appear the same from the air.
>
> So, FS9 has obtained, or built, a model of the entire earth that
> has assigned land classifications with a surface resolution of
> about 1.2 km square. This information is contained in the default
> file worldlc.bgl. This file assigns integer values of 0 - 255
> (not all are used in FS9) so there is a possibility of 256 different
> land classifications which could be assigned.
>
> FS9 uses the integer to map to a set of files in world\texture which
> represent the texture to be applied for that land class value. In
> addition to the texture file, 3D generic objects (called autogen)
> are tied to the files, to provide greater realism.
>
> In theory, it would only take 256 different texture files to serve the
> intended purpose, but this would be unsatisfactory for a couple reasons:
>
> 1. Night. At night there is little ambient lighting (though moonshine
> could be depicted) but there is artificial surface lighting. So this is
> modeled by having a set of night textures. These are blended in at
> dusk/dawn.
>
> 2. Seasons. In temperate zones, there can be a great deal of visual
> difference based on seasonal effects. FS9 uses a file seasons.bgl to
> select from a set of seasonal textures based on location and date.
>
> 3. Cultural effects. Land with human impacts (intensive agriculture
> or habitation) has a different visual appearance due to cultural
> differences. FS9 has a file reagons.bgl to select culturally-modified
> texture variations.
>
> 4. Checkerboard effect. When viewed from the air, the terrain textures
> at 1.2 km resolution would suffer from a tiling effect as the edge of
> each texture would be apparant, and the repeating nature of each tile
> (where several identical textures are placed side-by-side) would also
> reduce realism. FS9 attempts to get around this by having a set of
> textures with some visual variation, and the textures are blended with
> their neighboring textures on each of the 4 sides.
>
> 5. Performance issues. Note that the textures have default size of
> 256x256 pixels, but scenery displayed at a distance from the viewer
> doesn't need this level of accuracy, and so smaller versions
> (128x128, 64x64, etc) versions of each texture are stored and used in
> the distance.
>
> So, there a couple of ways to modify the land class system to change
> visual appearance. These can be summarized as:
>
> 1. Modify the worldlc.bgl to change the land classification value for
> a given position. This is what is commonly referred to as "land class"
> file.
>
> 2. Modify the textures in world\texture. The modified textures can
> have a different visual appearance, and also have different autogen
> objects assigned.
>
> 3. Modify the land class integer mapping system through seasons.bgl,
> regions.bgl, and lclookup.bgl. To the best of my knowledge, no one
> has successfully done this.
>
> Note that there is also a complementary system (though simpler) to
> deal with the visual appearance of water bodies. Also, the land class
> derived textures are modified by drawing terrain features over them
> (airport and park ground textures, roads, railroads, streams, etc).
> Finally, land class can be over-ridden by phototextures.
>
> scott s.
> .
>
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