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I had a problem with a complex model with a modled fence, the Rhino mesher need hours. So I try to use MOI (www.moi3d.com), because the mesher seems to work better and faster sometimes, meshes are looking cleaner.
I think, the infos I got are useful for everybody how want to create meshes of large, complex models.
I sended Michael from MOI an critical file and he wrote me:
I think, the infos I got are useful for everybody how want to create meshes of large, complex models.
I sended Michael from MOI an critical file and he wrote me:
Hi Micha, do you have to use .3ds format for this export?
Some limitations of that format seem to be causing difficulties.
#1 - 3DS is a very old format and uses 16-bit numbers for the mesh data.
This means that a single mesh in a 3DS file can only have up to 65535
vertices or polygons in it. Your object contains more polygons than that, so
it gets broken up pretty arbitrarily into different pieces so that each
piece fits within the 65535 limit.
#2 - 3DS can only contain triangle polygons in it, not polygons with more
sides. If you can export to OBJ format, it can handle polygons with more
than 3 sides which will simplify the output.
#3 - 3DS is not able to have vertex normals defined in the file for shading
information, programs that read 3ds files have to manually calculate
smoothing information just by averaging the normals for adjacent polygons
which tends to cause shading glitches. If you can export to OBJ instead,
vertex normals will be stored in the OBJ file which come from the original
NURBS surface data.
Especially #3 is a pretty big issue - the reason why a display mesh in MoI
looks as good as it does is because MoI uses the good vertex normals for
doing shading. If you were to take the display mesh and then try to render
it without the good normals you would see several problems.
One other additional problem with 3DS is that it only has up to 32
"smoothing groups" in the file. It looks like one of the main glitches in
your file is that some of the smoothing groups are being re-used, creating
some extra smoothing between some of the inside holes and the outer surface
that you don't want.
You should be able to get rid of extra smoothing by turning welding off
(expand the Meshing options dialog by clicking on the arrow in the
lower-left corner, and uncheck "Weld vertices along edges") - this will
export separated vertices for each surface which will prevent unwanted
smoothing.
So if you must use .3ds, turn off welding and I think your problem will be
solved.
The actual mesh polygon structure itself seems to be working fine for this
object, it looks like the re-use of smoothing groups after it loops around
the 32 group limit is causing the shading glitches. It may be possible for
me to fix this up a bit to try and assign the same smoothing group to
different pieces that don't touch one another.
I did a quick testing using OBJ export instead and it seems to generate a
good result.
I hope this helps!
- Michael
Some limitations of that format seem to be causing difficulties.
#1 - 3DS is a very old format and uses 16-bit numbers for the mesh data.
This means that a single mesh in a 3DS file can only have up to 65535
vertices or polygons in it. Your object contains more polygons than that, so
it gets broken up pretty arbitrarily into different pieces so that each
piece fits within the 65535 limit.
#2 - 3DS can only contain triangle polygons in it, not polygons with more
sides. If you can export to OBJ format, it can handle polygons with more
than 3 sides which will simplify the output.
#3 - 3DS is not able to have vertex normals defined in the file for shading
information, programs that read 3ds files have to manually calculate
smoothing information just by averaging the normals for adjacent polygons
which tends to cause shading glitches. If you can export to OBJ instead,
vertex normals will be stored in the OBJ file which come from the original
NURBS surface data.
Especially #3 is a pretty big issue - the reason why a display mesh in MoI
looks as good as it does is because MoI uses the good vertex normals for
doing shading. If you were to take the display mesh and then try to render
it without the good normals you would see several problems.
One other additional problem with 3DS is that it only has up to 32
"smoothing groups" in the file. It looks like one of the main glitches in
your file is that some of the smoothing groups are being re-used, creating
some extra smoothing between some of the inside holes and the outer surface
that you don't want.
You should be able to get rid of extra smoothing by turning welding off
(expand the Meshing options dialog by clicking on the arrow in the
lower-left corner, and uncheck "Weld vertices along edges") - this will
export separated vertices for each surface which will prevent unwanted
smoothing.
So if you must use .3ds, turn off welding and I think your problem will be
solved.
The actual mesh polygon structure itself seems to be working fine for this
object, it looks like the re-use of smoothing groups after it loops around
the 32 group limit is causing the shading glitches. It may be possible for
me to fix this up a bit to try and assign the same smoothing group to
different pieces that don't touch one another.
I did a quick testing using OBJ export instead and it seems to generate a
good result.
I hope this helps!
- Michael
