加法制造的过程中需要的原材料更少，因为3d印制机制由软件驱动，它可以制作所需的不同部件，而不用对每个不同部件进行耗材耗时的更换机械设备。
The additive process requires less raw material and, because software drives 3d printers, each item can be made differently without costly retooling.
正如以上所提到的，将不同的元素通过加法和减法的方式，慢慢地组合到一起是一个需要不断反复的过程。
As mentioned above, it was a very iterative process where all of the element were slowly built up together through additive and subtraction means.
在精确重建滤波过程中，需要计算投影数据的雷当变换，本文采用普通累加法和辛普森直线积分法来完成对象素网格的采样。
The Radon transform of the projection is calculated in the filtered process of exact reconstruction, Siddon and Simpson integral are used to sample the pixels to get the projection.
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