# [Gmsh] Points seem to move on transfinite surface after the recombination

Bojan Niceno bojan.niceno.scientist at gmail.com
Wed Jul 8 12:46:38 CEST 2020

```Dear all,

I have a problem when trying to mesh planar structured surfaces.  Although
points seem to be uniformly placed on a transfinite surface, they move a
bit when recombining the mesh to change triangles to quadrilateral cells.

Here is a simple script which demonstrates it:

// Define points
Point(1) = {0.0,  0.0,  0.0};
Point(2) = {0.5,  0.0,  0.0};
Point(3) = {0.0,  0.5,  0.0};
Point(4) = {0.7,  0.0,  0.0};
Point(5) = {0.0,  0.7,  0.0};

// Define connectors from points ...
Line  (1) = {2, 4};
Circle(2) = {4, 1, 5};
Line  (3) = {5, 3};
Circle(4) = {3, 1, 2};

// ... and set them as transfinite
Transfinite Curve {1, 2, 3, 4} = 11 Using Progression 1;

// Define surface ...
Curve Loop(1) = {1, 2, 3, 4};  Plane Surface(1) = {1};

// ... and set it as transfinite too
Transfinite Surface {1};

So, as I said, generating a 2D mesh over the surface places points
properly, but command recombine moves them a bit :-/  Is there a way to
prevent these movements of points?

I am also attaching a screenshot of a mesh before and after recombination,
to illustrate my problem better.

Best regards,

Bojan

P.S.  I am not sure if attachments go to the mailing list, I've never used
a mailing list before.
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```