Re: Triangle call unsuccessful

["David Meeker <dmeeker@xxxxxxxx>" <dmeeker@xxxxxxxx>]

--- In femm@xxxxxxxxxxxxxxx, "irishmist_ <djtim@xxxx>" <djtim@xxxx> wrote:
> Thanks for the comment Jiri. However, I think you missed my point. 
> I am very aware of the angle issue Dave has mentioned. Here is the 
> scenario... I am doing a DXF import... the tolerance dialog box 
> comes up on the screen and I change it to some number, say E-10 and 
> then try and run the mesher. I get the "Triangle can't run" message.
> 
> Take same DXF file and import leaving the tolerance at the default 
> value. Triangle runs without a problem. 
> 
> Identical geometry on import... one meshes --- one doesn't -- all 
> because of the tolerance setting during the file import.
> 
> Dan

I think that this is a case of things being ambiguous because of not
being very well documented. A problem with DXF files is that there
often isn't enough precision to ensure that points that coincide
actually do, etc. What the "tolerance" box represents is the maximum
distance between two points at which the DXF import routine considers
that two points should actually coincide.

The program picks some tolerance that ought to be "good enough", based
on the total dimensions of the problem. However, there can still
sometimes be problems. If there are problems, you actually want to
make the tolerance _larger_ so that that there is less chance of the
program missing two points which ought to actually coincide. You
generally don't want to make the tolerance smaller.

Even if a geometry does mesh successfully after DXF import, it is
important to check things to make sure that they are consistent --
e.g. no small gaps that cause a region which should be closed not to
be closed. If you look at the mesh generated, problem areas usually
concide with intersections where Triangle has placed an extremely high
density of triangles.

One more note--whenever you export a DXF file from a CAD program, make
sure to do it using the highest possible precision settings.

Dave.