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| NOTE: Some of the description below is of the status "Not Implemented Yet".
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| Marble provides a sophisticated layer framework.
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| Generally Marble is able to deal with several layers which can consist of different datasets ("SubLayers").
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| E.g. an aerial map could consist of three different layers:
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| * a layer that displays the aerial photo of the ground
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| * a layer that shows the roads
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| * a layer that shows clouds.
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| In this case there would be three texture mapper objects needed. And each of them would deal with tiles that only consist of a single dataset.
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| Alternatively an aerial map could also consist of a single layer which consists of different datasets that get merged together for each tile:
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| * a dataset that displays the aerial photo of the ground
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| * a dataset that shows the roads
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| * a dataset that shows clouds.
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| In this case there would only be a single texture mapper object. This single texture mapper would deal with tiles that contain all three datasets merged into a single tile.
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| The class design works like this:
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| =TextureMapper=
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| For different projections and backends there exist different texture mapping classes. Each of these derives from the AbstractTextureMapper class.
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| The texture mapping classes get the tiles that they need for texture mapping from the TileLoader Class.
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| =TileLoader=
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| The TileLoader class provides tile data needed for texture mapping. All tiles exist as objects of the type TextureTile (or: AbstractTile).
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| As such it ensures that all tiles that are currently in use are kept in memory.
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| It also ensures that depending on the distance to the ground there is a preferred tile level in use.
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| All tiles that are currently displayed go into the TileHash. The tiles which have just recently been used go into the TileCache.
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| =TextureTile=
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| =DatasetProvider=
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