用二叉树表示二维图形的一个重要优点是层次分明。
Ohe of the important advantages of representing 2-d shape by binary tree its clear hierarchy.
国内在将二维CAD及其软件用于低层次的绘图很普及，但自主开发的三维CAD系统还未成熟。
The two-dimension CAD and its software of low layer are being used to draw is very popular, but the three-dimensional CAD system of independent development is still immature in domestic.
水质数学模型的研究按照空间层次可以划分为一维、二维、三维模型和水系模型、模型系统。
According to spatial levels, water quality model may be divided into one dimension model, two dimension model, three dimension model, watershed model and model system.
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