简介

编辑模式下的NURBS曲面。

You may ask yourself "but the surface appears to be 3D, why is it only 2D?".In order to be 3D, the object needs to have "Volume", and a surface, even when it is closed,does not have volume; it is infinitely thin.If it had a volume the surface would have a thickness (its third dimension). Hence,it is only a 2D object, and has only two interpolation dimensions or axes or coordinates(if you know a bit of math, think of non-Euclidean geometry — well,surfaces are just non-Euclidean 2D planes…). To take a more "real-world" example,you can roll a sheet of paper to create a cylinder; well, even if it becomes a "volume",the sheet itself will remain a (nearly…) 2D object!

正如图 中看到的，除了U向坐标是用黄色的网格线，V向坐标是由粉红网格线标识出来之外，曲面跟NURBS曲线几乎没有区别。