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# Re: Triangle call unsuccessful

- To: femm@yahoogroups.com
- Subject: Re: Triangle call unsuccessful
- From: "irishmist_ <djtim@worldnet.att.net>" <djtim@worldnet.att.net>
- Date: Thu, 06 Feb 2003 18:16:02 -0000
- In-reply-to: <b1tpkq+le19@eGroups.com>
- User-agent: eGroups-EW/0.82

    Dave,

    Thanks for detailed explanation. Now I fully understand what is
    going on with the import considering the geometry I have why the
    tighter tolerance would cause meshing failure. I was thinking the
    tolerance was more for precision not gap closing.

    Dan

    --- In femm@yahoogroups.com, "David Meeker <dmeeker@i...>"
    <dmeeker@i...> wrote:
    > --- In femm@yahoogroups.com, "irishmist_ <djtim@w...>" <djtim@w...>
    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.

- References:
  - Re: Triangle call unsuccessful
    - From: "David Meeker <dmeeker@ieee.org>" <dmeeker@ieee.org>

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