[Gmsh] gmsh problem with 2d mesh

[krazz at ceoc.com]

hello,

I am currently writing an export filter to produce gmsh-readable .geo
files from VTK mesh data to be able to compare different meshing tools
and algorithms.
Unfortunately I ran into a problem using gmsh (CYGWIN_NT-5.1
1.3.22(0.78/3/2) on a windows xp machine) - here is part of a file that
will produce erroneous output:

Point(1540) = {110.000000, 82.000000, 165.000000, lc};
Point(40) = {110.000000, 84.000000, 167.000000, lc};
Point(1538) = {112.000000, 84.000000, 167.000000, lc};
Line(1) = {40, 1540};
Line(2) = {40, 1538};
Line(3) = {1538, 1540};
Line Loop(4) = {-1, 2, 3};
Plane Surface(5) = {4};
Physical Surface(6) = {5};
Point(8234) = {119.000000, 82.000000, 167.000000, lc};
Point(786) = {112.000000, 86.000000, 169.000000, lc};
Point(4528) = {114.000000, 86.000000, 171.000000, lc};
Line(7) = {786, 8234};
Line(8) = {786, 4528};
Line(9) = {4528, 8234};
Line Loop(10) = {-7, 8, 9};
Plane Surface(11) = {10};
Physical Surface(12) = {11};
Point(2249) = {119.000000, 82.000000, 171.000000, lc};
Point(5276) = {114.000000, 86.000000, 173.000000, lc};
Point(3750) = {112.000000, 86.000000, 177.000000, lc};
Line(13) = {2249, 5276};
Line(14) = {3750, 5276};
Line(15) = {2249, 3750};
Line Loop(16) = {13, -14, -15};
Plane Surface(17) = {16};
Physical Surface(18) = {17};
Surface Loop(9500) = {5, 11, 17};

in this example, for lc <= 2 gmsh will produce a 2d mesh as it should,
but with lc=4 for example, it will give me an error message saying "No
triangles in surface mesh" or produce new lines from the 1d mesh points
of the line loop(16) to infinity in some direction

The problem seems to occur as soon as the triangles that I export are
small compared to lc. How do these values depend on eachother, or to put
it another way, how can I compute the minimum value for the
characteristic length of a triangle, so that gmsh will use it correctly?

Another question, is there a real windows port of gmsh available, that
will compile with Visual C++ for example? I have spent quite some time
trying to get the library to work without cygwin, but no success..

I hope to hear from you soon
greetings,
Nikolaus Völzow