# Problem interpolating between meshes

**URL:** https://community.freefem.org/t/problem-interpolating-between-meshes/1074
**Category:** General Discussion
**Created:** [July 1, 2021, 5:05pm UTC](https://community.freefem.org/t/problem-interpolating-between-meshes/1074 "2021-07-01T17:05:07Z")
**Posts on this page:** 4
**Page:** 1

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### Author: ![lparras](https://yyz2.discourse-cdn.com/flex030/user_avatar/community.freefem.org/lparras/32/544_2.png) [@lparras](https://community.freefem.org/u/lparras)
#### Post date: [July 1, 2021, 5:05pm UTC](https://community.freefem.org/t/problem-interpolating-between-meshes/1074/1 "2021-07-01T17:05:07Z")

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Dear all.

I am having an issue interpolating between two meshes. I have a first mesh like the first figure provided by other code

 ![image](https://canada1.discourse-cdn.com/flex030/uploads/freefem/original/1X/6713a4655ba917656314d7c8e2dfdcf43cb9e418.png) .

I have defined a mesh in the same domain (in FreeFem) and interpolated the data from one mesh to the other. I found that the points near the surface of the square cylinder are not properly calculated. I have read in the documentation (page 196) that to speed-up the process the interior of the objects are also triangulated. That can be the reason of this variation?

 ![image](https://canada1.discourse-cdn.com/flex030/uploads/freefem/original/1X/75c7d515804f35ca44b65e93232a31641c1c2979.png)

How can I solve this problem?

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### Author: ![frederichecht](https://yyz2.discourse-cdn.com/flex030/user_avatar/community.freefem.org/frederichecht/32/15_2.png) [@frederichecht](https://community.freefem.org/u/frederichecht)
#### Post date: [July 3, 2021, 5:13pm UTC](https://community.freefem.org/t/problem-interpolating-between-meshes/1074/2 "2021-07-03T17:13:56Z")

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Can you send the 2 meshes to see what is the problem,  
and also say which is the finite element.

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### Author: ![lparras](https://yyz2.discourse-cdn.com/flex030/user_avatar/community.freefem.org/lparras/32/544_2.png) [@lparras](https://community.freefem.org/u/lparras)
#### Post date: [July 12, 2021, 8:49am UTC](https://community.freefem.org/t/problem-interpolating-between-meshes/1074/3 "2021-07-12T08:49:12Z")

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Dear Frederic.

Thanks for the interest. I have used P1 FEM. I send to you the meshes, the solution files and a edp file to read and perform the interpolation.

Best regards.-  
[InterpolationProblem.targz](https://community.freefem.org/uploads/short-url/ik2L4TU2GPN3gBDwt3L9kDXvThi.targz) (912.3 KB)

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<div class="post-metadata">

### Author: ![frederichecht](https://yyz2.discourse-cdn.com/flex030/user_avatar/community.freefem.org/frederichecht/32/15_2.png) [@frederichecht](https://community.freefem.org/u/frederichecht)
#### Post date: [July 15, 2021, 7:58pm UTC](https://community.freefem.org/t/problem-interpolating-between-meshes/1074/4 "2021-07-15T19:58:30Z")

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I thing the problem do not come from freefem++

I have try to see the solution close the square

[readMeshesInterpolate.edp](https://community.freefem.org/uploads/short-url/zQVUVLTgDUPowx2XzufDLBsLsiV.edp) (1012 Bytes)