Coordinate

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Coordinate

Cartesian

The most common way of describing and delineating 3D space. Space is delineated by three vectors at right angles to each other, labeled by longtime convention as X, Y, and Z, and starting at a center point called the Origin. This coordinate system is based on the ideas of Rene Descartes, aka Cartesius of the "Cognito ergo sum" fame (I think, therefore I am). It is a very efficient way to describe space, so most RT3D engines use this system.

Positional

Coords for short, these are the numbers that tell the engine where to position things, whether in 3D or in 2D (like a polygon or an overlay). If positioning something in 3D, you need three coords, commonly called X, Y, and Z, and usually written as (X,Y,Z). If positioning something in 2D, you only use the X and the Y, and write it as (X,Y). For 2D, the X is horizontal, the Y is vertical, and the numbers usually start at (0,0) in the upper-left corner. But for 3D, Y is not always vertical.

Texture

These are the numbers that tell the engine where to position 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.

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. Numbers higher than 1.0 will make the texture tile, and negative numbers will 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 numbers that these shapes create for the polygons.

Also called mapping coordinates.

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