# [Gmsh] Spline surfaces

Roy Bijster - 3ME R.J.F.Bijster at tudelft.nl
Fri Apr 7 16:19:07 CEST 2017

```Dear GMSH community,

I am currently struggling with Spline/BSpline surfaces.

I am trying to define a surface that is defined by splines over both axes. For an example, see below.
When I only divide the surface into three adjacent strips, I loose the smooth curves in the perpendicular direction. Subdiving the surface in nine equal patches is also not an option, because this will yield linear splines between the defined points, rather than the smooth curves over the domain.

Is this at all possible via a GEO file and if so, how?
Ideally it would be using NURBS surfaces, but I understand that this is currently only supported for imported STEP files and the like.

You help would be greatly appreciated!

Best regards,

Roy Bijster
Structural Optimization and Mechanics
Precision and Microsystems Engineering
Faculty Mechanical, Maritime and Materials Engineering
Delft University of Technology

// ---- GEO FILE --------------------------------------------
Point(1) = {0, 0, 0}; Point(2) = {1, 0, 0}; Point(3) = {2, 0, 0}; Point(4) = {3, 0, 0};
Point(5) = {0, 1, 0}; Point(6) = {1, 1, 2}; Point(7) = {2, 1, -1}; Point(8) = {3, 1, 0};
Point(9) = {0, 2, 0}; Point(10) = {1, 2, -0.5}; Point(11) = {2, 2, 1}; Point(12) = {3, 2, 0};
Point(13) = {0, 3, 0}; Point(14) = {1, 3, 0}; Point(15) = {2, 3, 0}; Point(16) = {3, 3, 0};

Spline(1) = {1, 2, 3, 4};
Spline(2) = {5, 6, 7, 8};
Spline(3) = {9, 10, 11, 12};
Spline(4) = {13, 14, 15, 16};
Spline(5) = {1, 5, 9, 13};
Spline(6) = {2, 6, 10, 14};
Spline(7) = {3, 7, 11, 15};
Spline(8) = {4, 8, 12, 16};
// ---- END OF GEO FILE --------------------------------------------

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