UVW coordinates, also called mapping coordinates, are the values that tell the engine where to position textures on mesh. The engine uses three texture coordinates, commonly called U, V, and W. U is the width of the texture, V is the height, and W is used for depth if you are using a 3D procedural texture.
A texture’s U and V values range from 0 to 1.
The coordinates are measured in a scale of 0.0 to 1.0, with 0.0 and 1.0 at opposite sides of the texture. When a texture is set to Repeat (for tiling) instead of Clamp, numbers higher than 1.0 make the texture tile, and negative numbers mirror the texture.
With most 3D modeling software, these numbers are usually hidden from the artist, replaced by helpful visual representations of how the textures are projected. Planes, cylinders and spheres help the artist align the textures in a visual way, but it helps to know that engines see only the UVW values that these shapes create for the polygons.
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