[Gmsh] nodes don't align with geometry for simple rectangle

Al Danial al.danial at gmail.com
Thu Aug 25 05:39:28 CEST 2005


Here's something curious:  I create a rectangle having dimensions
of 6 x 2 units with

Point(1) = {0, 0, 0, 0.5};
Point(2) = {6, 0, 0, 0.5};
Point(3) = {6, 2, 0, 0.5};
Point(4) = {0, 2, 0, 0.5};
Line (1) = {1, 4};
Line (2) = {2, 3};
Line (3) = {4, 3};
Line (4) = {1, 2};
Line Loop (1000006) = {1, 3, -2, -4};
Ruled Surface (6) = {1000006};

then mesh it with triangular elements.  It gives 66 nodes and
130 elements and visually the nodes along the boundary line 
up perfectly with the geometric Line entities.  So far, so good.

However when I save the mesh, the nodal coordinates on the 
right edge don't match the geometry.  Node 3, which is located
where Point 3 is, has coordinates of 5.7, 1.9 instead of
6.0, 2.0.  In fact all nodes on the right edge of the rectangle
have an X value of 5.7 instead of 6.0, and all nodes on the top 
edge have a Y value of 1.9 instead of 2.0.

I'm using version 1.60-1 (via Debian apt-get).

Any hints as to why my boundary nodes don't match the
geometric boundary?            -- Al