在计算机图形学中，UVW 贴图和 UV 贴图有什么区别？
在处理纹理时，“UVW 贴图”与“UV 贴图”含义相同吗？
如果是这样，为什么有两个术语，“W”是什么？ 如果不是，它们之间有什么区别？
[维基百科目前没有阐明这个问题：http://en.wikipedia.org/wiki /讨论：UVW_mapping]
In working with textures, does "UVW mapping" mean the same thing as "UV mapping"?
If so why are there two terms, and what is the "W"?
If not, what's the difference between them?
[Wikipedia currently isn't illuminating on this question: http://en.wikipedia.org/wiki/Talk:UVW_mapping]
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U 和 V 是 2D 地图的坐标。添加 W 分量会增加第三个维度。
至少可以说，实际手动生成 3D 纹理贴图是很乏味的，但如果您有生成纹理数据的程序方法，它们就会很有用。例如，如果您希望对象看起来像一块实心大理石，那么最简单的方法可能是将大理石“纹理”“建模”为 3D 程序纹理，然后使用 3D 坐标从程序纹理中绘制数据。
U and V are the coordinates for a 2D map. Adding the W component adds a third dimension.
It's tedious to say the least to actually hand generate a 3D texture map, but they are useful if you have a procedural way to generate texture data. E.g. if you wanted your object to look like it's a solid chunk of marble, it may be easiest to "model" the marble "texture" as a 3D procedural texture and then use 3D coordinates to draw data out of the procedural texture.
UVW 相对于 XYZ 就像 XYZ 相对于世界坐标一样。由于 XYZ 已用于指代世界坐标，因此 UV 用于指代平面地图的 X 和 Y (2D) 坐标。通过外推，W 就是 XYZ 中的 Z。
UVW 推断出更复杂的 2D 表示，它实际上是从 3D 对象“展开”的对象的皮肤。想象一个“打开”的盒子。您现在拥有了一个平面 UVW 贴图，您可以在其上绘制您想要的内容，然后将其无变形地包裹回六面盒子上。简而言之，UVW 贴图知道在哪里重新包裹 x、y 和 z 点以重组盒子。
现在想象一个“展开”的球体。您最终可能会得到类似墨卡托投影的结果。问题是，对于这个问题，当你将这个二维表示重新包装到球体上时，你会得到一些扭曲。
UV 映射一词非常常用。除了上面描述的情况外，我不经常听到 UVW 这个词。
术语“程序映射”可能会产生误导。简而言之，这意味着计算机遵循一些算法将材料（例如木材）的真实表示绘制到物体上，给您一种纹理完全穿过木材的印象，因此可以在木材的两面正确看到它。目的。程序映射可以使用图像，也可以不使用图像，也可以使用多种方法的组合……这一切都取决于“程序”。
最后，不需要首先将“3d 程序纹理”转换为“UVW”，因为 UVW 和 XYZ 实际上意味着相同的事物 - 它们要么指的是世界，要么指的是世界上物体的展开图像，或者就世界的“块”而言，就像天空中的那样。重点是UV或UVW指的是图像/纹理映射。
UVW is to XYZ as XYZ is to world coordinates. Since XYZ was already being used to refer to world coordinates, UV is used to refer to the X and Y (2D) coordinates of a flat map. By extrapolation, the W is the Z in XYZ.
UVW infers a more complex 2d representation which is, in effect, the skin of the object that has been 'unwrapped' from a 3d object. Imagine a box 'unwrapped'. You now have a flat UVW map that you can paint on to your hearts content and then wrap back onto the six-sided box with no distortion. In short the UVW map knows where to rewrap the x, y and z points to reform the box.
Now imagine a sphere 'unwrapped'. You might end up with something like a Mercator projection. The hitch is that with this problem, when you wrap this 2d representation back onto the sphere, you will get some distortion.
The term UV mapping is very commonly used. I don't hear the term UVW as often except as described above.
The term procedural mapping can be misleading. Simply put, it means the computer is following some algorithms to paint a realistic representation of a material, like wood, onto the object, giving you the impression that the grain travels completely through the wood so it can be seen properly on both sides of the object. Procedural mapping can use images or not, or a combination of approaches...it all depends on the 'procedure'.
Lastly, there is no requirement to transform a '3d procedural texture' to 'UVW' first, since UVW and XYZ mean effectively the same thing - they are either referring to the world, or an unwrapped image of on object in the world, or for that matter of a 'chunk' of the world, as in the sky. The point is that UV or UVW refers to image/texture mapping.