Is there more infomation about the notion of orientation?

Yi Zhou's picture
Yi Zhou
Wed, 07/17/2024 - 07:31
Forums: 
Modeling Data and Algorithms

Hello, I am reading the OCCT User Guides - Modeling Data. And I am confused in the otion of orientation.

First,What's the meanning of "/" and "\" on the figure1?

Second,I could not find more infomation about the notion of "orientation" on wikipidia.
The page i found is this "https://en.wikipedia.org/wiki/Orientation_(geometry)".

I also can not understand about the four orientation "Based on this default region the orientation allows definition of the region to be kept, which is called the interior or material. There are four orientations defining the interior."

Can you guys help me to find some books or pages about these four orientation-"forward, reversed, internal ,external"?

Any words from you guys can be helpful to me!
Thank you!

Attachments: 
Image icon figure1.png
Farley Runkel's picture
Farley Runkel
Thu, 08/15/2024 - 10:03

你好啊，"/" and "\"，只是代表默认区域的阴影线，为了通过边界精确地描述几何体的内外部区域， OCCT规定了面的 默认区域 为边的左侧区域。随之定义4个方向，用于确定内部区域：

  • FORWARD：默认区域被视为内部区域。
  • REVERSED：内部区域是默认区域的补集，即默认区域外的部分。
  • INTERNAL：内部区域包括两个区域，边界位于材料内部。
  • EXTERNAL：内部区域既不包括默认区域也不包括补集，边界位于材料外部。

而曲线的默认区域是参数大于点的区域，也就是说，对于一个B样条曲线定义的线段来说，它的起点是FORWARD方向，而终点是REVERSED方向。 希望可以帮助你理解