# How can I constrain a line's midpoint to another line or midpoint?

**URL:** <https://discourse.shapr3d.com/t/how-can-i-constrain-a-lines-midpoint-to-another-line-or-midpoint/35125>\
**Category:** Modeling Questions\
**Created:** [November 12, 2024, 12:07am UTC](https://discourse.shapr3d.com/t/how-can-i-constrain-a-lines-midpoint-to-another-line-or-midpoint/35125 "2024-11-12T00:07:10Z")\
**Posts on this page:** 4\
**Page:** 1

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**Author:** ![Mindful\_Mayhem](https://avatars.discourse-cdn.com/v4/letter/m/9de053/32.png) [@Mindful\_Mayhem](https://discourse.shapr3d.com/u/Mindful_Mayhem)\
**Post date:** [November 12, 2024, 12:07am UTC](https://discourse.shapr3d.com/t/how-can-i-constrain-a-lines-midpoint-to-another-line-or-midpoint/35125/1 "2024-11-12T00:07:10Z")

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I can get the midpoints aligned, as shown in the screenshot, but I want it to be anchored to the horizontal line so that when I change variables (angle, length) it will pivot or stretch symmetrically with its midpoint staying on the horizontal line or its midpoint.

 ![midpoints](https://us1.discourse-cdn.com/flex002/uploads/shapr3d/original/3X/f/e/fefc44947c7fedad7e28e94fca50dcb3e404067b.png)

I’ve found some similar posts but they only show how to align the midpoints, not constrain them, and many of them were old and seemed outdated, or had broken links/missing videos.

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**Author:** ![charly44300](https://sea2.discourse-cdn.com/flex002/user_avatar/discourse.shapr3d.com/charly44300/32/27971_2.png) [@charly44300](https://discourse.shapr3d.com/u/charly44300)\
**Post date:** [November 12, 2024, 8:45am UTC](https://discourse.shapr3d.com/t/how-can-i-constrain-a-lines-midpoint-to-another-line-or-midpoint/35125/2 "2024-11-12T08:45:22Z")

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Il suffit de bloquer ici le segment horizontal avec la contrainte cadenas.

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**Author:** ![Oregonerd](https://sea2.discourse-cdn.com/flex002/user_avatar/discourse.shapr3d.com/oregonerd/32/8012_2.png) [@Oregonerd](https://discourse.shapr3d.com/u/Oregonerd)\
**Post date:** [November 12, 2024, 3:16pm UTC](https://discourse.shapr3d.com/t/how-can-i-constrain-a-lines-midpoint-to-another-line-or-midpoint/35125/3 "2024-11-12T15:16:47Z")

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If you cannot select the center purple dot and lock it. Maybe you could draw a short segment (construction line) ending at the center of both lines. That should give you a point to lock in the constraints?

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**Author:** ![PEC](https://avatars.discourse-cdn.com/v4/letter/p/67e7ee/32.png) [@PEC](https://discourse.shapr3d.com/u/PEC)\
**Post date:** [November 12, 2024, 5:44pm UTC](https://discourse.shapr3d.com/t/how-can-i-constrain-a-lines-midpoint-to-another-line-or-midpoint/35125/4 "2024-11-12T17:44:50Z")

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At present you cannot constraint 2 midpoints to be coincident without using a third (construction) line ending at the mid points, as @Oregonerd suggested, because midpoint constraint works only with end point : you select an end point and then a line and then apply midpoint constraint.

The other way is to draw two lines, starting at the mid point of the horizontal line, and set 2 constraints on both of them:

- Equal
- Tangent