# [Gmsh] problem with 2D geometry representation?

**Hugh Blackburn**
hugh.blackburn at gmail.com

*Mon May 10 19:01:56 CEST 2010*

Hi there,
Found something funny (or maybe I just did not understand) here. The
following code draws a segment of a circle as an inner part and out
part (the curves are drawn using Circle). But the arcs seem
distorted: when I draw two points that ought to lie on the arcs
(Points 6 and 7) they are visibly away from the curves. I found this
also when I tried to use extrude to do the generation: the curves that
came out of Extrude did not match those drawn by Circle. What is
wrong?
(I have left off the parts of the file associated with meshing: I'm
still worried that the geometry is incorrect.)
TIA
Hugh
// -- 2D mesh algorithm: 1=MeshAdapt, 5=Delaunay, 6=Frontal
Mesh.Algorithm=1;
// -- All-quad mesh:
Mesh.SubdivisionAlgorithm=1;
lc1 = 0.1;
lc2 = 0.1;
rad = 0.5;
san = Pi/5.;
Point(1) = {0, 0, 0, lc1};
Point(2) = {-0.8*rad*Sin(san), -0.8*rad*Cos(san), lc2};
Point(3) = { 0.8*rad*Sin(san), -0.8*rad*Cos(san), lc2};
Point(4) = {-1.0*rad*Sin(san), -1.0*rad*Cos(san), lc2};
Point(5) = { 1.0*rad*Sin(san), -1.0*rad*Cos(san), lc2};
Point(6) = {0, -0.8*rad, lc2};
Point(7) = {0, -rad, lc2};
Line(1) = {2, 1};
Line(2) = {1, 3};
Circle(3) = {2, 1, 3};
Line(4) = {4, 2};
Line(5) = {3, 5};
Circle(6) = {4, 1, 5};
--
Hugh Blackburn
Associate Professor
Department of Mechanical and Aerospace Engineering
Monash University
Vic 3800
Australia
Building 31, Rm 119
Tel: +61-3-9905-1828
Fax: +61-3-9905-3558
mailto:hugh.blackburn at eng.monash.edu.au
http://users.monash.edu.au/~bburn