# How to judge whether the order of 2 groups of points in 3D space has changed in space?

**URL:** <https://discourse.slicer.org/t/how-to-judge-whether-the-order-of-2-groups-of-points-in-3d-space-has-changed-in-space/24826>\
**Category:** Development\
**Tags:** python\
**Created:** [August 19, 2022, 5:00am UTC](https://discourse.slicer.org/t/how-to-judge-whether-the-order-of-2-groups-of-points-in-3d-space-has-changed-in-space/24826 "2022-08-19T05:00:15Z")\
**Posts on this page:** 1\
**Showing post:** 5

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**Author:** ![jumbojing](https://sea2.discourse-cdn.com/flex002/user_avatar/discourse.slicer.org/jumbojing/32/10811_2.png) [@jumbojing](https://discourse.slicer.org/u/jumbojing)\
**Post date:** [August 21, 2022, 2:30pm UTC](https://discourse.slicer.org/t/how-to-judge-whether-the-order-of-2-groups-of-points-in-3d-space-has-changed-in-space/24826/5 "2022-08-21T14:30:07Z")

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这个问题困惑了我好久–就是如何判断表面是否闭合, 尝试过一些方法都不理想, 后来我发现生成的点云的顺序在闭合时,按一定方向(这里是顺时针)规律排布, 而非闭合时, 其空间顺序发生了改变, 所以就有了上面👆🏻这个问题

> This question has puzzled me for a long time - how to judge whether the surface is closed…I have tried some methods, but none of them are ideal.Later, I found that the order of the generated point clouds is arranged in a certain direction (clockwise here) when it is closed, but when it is not closed, its spatial order has changed, so there is the above problem 👆🏻.  
> [How to extract the vertex coordinates of a polygon of a model in the current section?](https://discourse.slicer.org/t/how-to-extract-the-vertex-coordinates-of-a-polygon-of-a-model-in-the-current-section/24380)  
> [How to judge a curve model obtained with vtkplanecut or vtkcutter is closed?](https://discourse.slicer.org/t/how-to-judge-a-curve-model-obtained-with-vtkplanecut-or-vtkcutter-is-closed/24470)

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