From: Charles Overy (cwho@lgmmodel.com)
Date: Wed Sep 24 2003 - 21:06:12 EEST
Jonathan
> I had been using an extended demo version of Materialise Magics and I am
> afraid I have been really spoiled.
Magics is the gold standard, you just have to have a lot of gold. We need
to take another look at them as it seems they are really the only stl prep
program with ALL the features. It seems to me, you have to give up some
significant functions if you go other routes.
> I've recently started using Rhino and have some familiarity with Form Z.
> Neither seem to offer a particularly visual way to view the
> "validity" of an
> stl file.
In some ways you gain flexibility by using a general purpose CAD program but
it can also take a great deal longer in difficult cases. I think the answer
really depends on the type of geometry you usually process. Your sculptures
for instance are fairly easy to patch as they only have an exterior surface.
However, shelling many of them to reduce material usage is very difficult in
cases involving acute angles because a simple surface offset to the inside
creates self intersecting surfaces.
FormZ is very "tough" on STL. It will not export anything but watertight
solids. That has good and bad effects. The ZCorp software is a little
more forgiving in accepting geometry that is not truly valid. So often
times we want to export geometry that is technically not correct but we know
will run. (We know this based on trial and error). The end run for this is
to use 3ds as an export and then a tool like decompress or Deep Exploration
to go from 3ds to stl. Patching in FormZ is possible but time consuming.
The most difficult part is trying to find the bad or missing triangles, as
there is not any "automatic" way to detect them. You have to use various
rendering modes depending on what errors you think you might find. We only
have one person in the shop who is proficient at Rhino so I cannot say that
much except that we seem to get good files from it and one customer used it
as an stl generator for data from Maya.
One thing we have been meaning to try in more depth is to use a combination
of STL Editor from Floating Point Solutions and the Rhino plugins from the
same company. The good thing about STL editor, (in addition to its $500
price tag) is that it will do offset and shelling. STL editor has very good
flipped normal indication but it is not good as a repair program. I think
the product has now been replaced by a program called MeshWorks.
> I also have a demo version of STLViewer that [seems] to allow me to see
> models in a way similar to some jpg's I have seen from Solidview etc.
>
> 1. Can anyone recommend a real solid STL Viewer that would allow
> me to see a
> file similar to RP Vendors? Deskartes Viewer?
>
> 2. What commands or queries do Vendors run in order to see if a file will
> shoot through their machine? And is there some "play" in this
> deliberation?
>
Lots of play but it always seems like work... I have put a request in to
Zcorp to release a simplified, stripped down, file "proofer" or viewer
specifically to allow 3rd parties to see if their files are printable. It
would be useful as that is really the only way to tell. You can otherwise
chase a lot of issues making the file perfect that do not need to be fixed.
Primarily Boolean - ing multiple solids is usually not necessary,
depending on how the solids touch each other and if the machine is being run
with bleed compensation on or off. I am sure the issues are different for
other machines. Please could other comment if they are.
> 3. Can anyone out there who uses Rhino share their experience
> with "fixing"
> stl's for RP - and/or - explain which queries they use to decide
> if the stl
> file is valid.
>
> 4. Anyone find Form Z (or other) software more convenient than Rhino for
> either BOOLEAN OPERATIONS or stl fixing?
Personally, I would not buy FormZ or Rhino if my primary purpose was stl
prep. Have a look also at Marcam Engineering products also.
>
> 5. I've got some nasty little shapes that seem to come up in STLViewer as
> radially alternating multi-colors, which I assume means they have their
> normals alternating in a radiul pattern as well.
Could possibly be duplicate coincident faces as well. Do the colors of the
faces look the same from every angle or do they change with viewing angle?
If they change it is coincident faces.
Is viewing the
> validity of
> an stl file in a viewer as simple as checking to see if there are
> aberrantly
> colored surfaces?
No, that will not tell you if the mesh is watertight and topologically
correct. Also do not forget about fully enclosed geometry. If you are
looking at the exterior shell, do you have any hidden geometry? For large
objects you also need to look at shelling the object to reduce material
costs.
Please post back to the list any other info you might get or your
experiences.
Thanks
Charles
LGM
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