# Region Union Bug

**URL:** <https://discourse.mcneel.com/t/region-union-bug/118605>\
**Category:** Grasshopper\
**Created:** [February 16, 2021, 5:56am UTC](https://discourse.mcneel.com/t/region-union-bug/118605 "2021-02-16T05:56:13Z")\
**Posts on this page:** 5\
**Page:** 1

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**Author:** ![Chris\_Lim](https://sea3.discourse-cdn.com/mcneel/user_avatar/discourse.mcneel.com/chris_lim/32/284289_2.png) [@Chris\_Lim](https://discourse.mcneel.com/u/Chris_Lim)\
**Post date:** [February 16, 2021, 5:56am UTC](https://discourse.mcneel.com/t/region-union-bug/118605/1 "2021-02-16T05:56:13Z")

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![region_union_issue](https://global.discourse-cdn.com/mcneel/uploads/default/original/4X/3/3/4/3345d4287c790dda9eef77bb913109aebc87900e.png)

Region Union doesn’t seem to be working.  
Some region is missing.  
[ghcomp\_region\_union\_issue.gh](https://discourse.mcneel.com/uploads/short-url/rVacykViy3gBd7za74VhH5QVcQU.gh) (6.6 KB)

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**Author:** ![HS\_Kim](https://sea3.discourse-cdn.com/mcneel/user_avatar/discourse.mcneel.com/hs_kim/32/473975_2.png) [@HS\_Kim](https://discourse.mcneel.com/u/HS_Kim)\
**Post date:** [February 16, 2021, 6:50am UTC](https://discourse.mcneel.com/t/region-union-bug/118605/2 "2021-02-16T06:50:53Z")

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If you force to make the two polylines have the same starting point, then It seems to works but still to be a buggy behavior.

 ![Canvas at 15;43;31](https://global.discourse-cdn.com/mcneel/uploads/default/original/4X/b/7/9/b797b35493f06b2668c629457a1109eeabfb18b9.jpeg)  
[ghcomp\_region\_union\_issue\_re.gh](https://discourse.mcneel.com/uploads/short-url/aR6U7qrYZyjHvi8rfkckVkOCQxJ.gh) (7.4 KB)

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**Author:** ![martinsiegrist](https://sea3.discourse-cdn.com/mcneel/user_avatar/discourse.mcneel.com/martinsiegrist/32/498369_2.png) [@martinsiegrist](https://discourse.mcneel.com/u/martinsiegrist)\
**Post date:** [February 16, 2021, 8:04am UTC](https://discourse.mcneel.com/t/region-union-bug/118605/3 "2021-02-16T08:04:22Z")

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Scaling the two curves by factor 1.0001 and the union works fine. It may not be a solution but it could prove that this is a tolerance problem.

Overlapping geometry is generally better for boolean operations / unions / intersections and such…

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**Author:** ![anon39580149](https://avatars.discourse-cdn.com/v4/letter/a/977dab/32.png) [@anon39580149](https://discourse.mcneel.com/u/anon39580149)\
**Post date:** [February 16, 2021, 8:21am UTC](https://discourse.mcneel.com/t/region-union-bug/118605/4 "2021-02-16T08:21:31Z")

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In many cases like this **Fit curve** solve the problem

 ![image](https://global.discourse-cdn.com/mcneel/uploads/default/original/4X/d/a/b/dab8a0e71ba6e963b54dbaf25ab9d1a2fd11b459.png)

 ![image](https://global.discourse-cdn.com/mcneel/uploads/default/original/4X/d/d/2/dd200b40d055a2a9ad691a0c1b2a36d036a8b774.png)

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**Author:** ![Chris\_Lim](https://sea3.discourse-cdn.com/mcneel/user_avatar/discourse.mcneel.com/chris_lim/32/284289_2.png) [@Chris\_Lim](https://discourse.mcneel.com/u/Chris_Lim)\
**Post date:** [February 16, 2021, 10:25am UTC](https://discourse.mcneel.com/t/region-union-bug/118605/5 "2021-02-16T10:25:05Z")

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Thanks a lot! It works well!