Subject:
|
Re: stl2dat conversion tool beta2
|
Newsgroups:
|
lugnet.cad.dev
|
Date:
|
Fri, 11 Feb 2000 20:29:56 GMT
|
Reply-To:
|
RUI.MARTINS@nomorespamLINK.PT
|
Viewed:
|
1187 times
|
| |
|
|
> > Does STL allow only for triangles ? no Quads ? no N sided Polygons ?
>
> No ONLY Triangles. Look for STL format description
> http://www.eng.clemson.edu/~wfeng/stl_fmt.htm
> http://www.sdsc.edu/tmf/Stl-specs/stl.html
> http://www.ennex.com/fabbers/StL.sht
Thanks for this info, I couldn't find it on WOTSIT's site.
> > > > Buy the way, do you correctly generate these lines (expecially the
> > > > optional ones) ?
>
> > <SNIP>
>
> The program check the angle between two adjacent facets
> if abs(angle ) < 1e-5
> No Edge
> if abs(angle) < 45°
> Optional Edge
> else
> Normal Edge
Both those constant should be configurable, eventually within
predefined ranges.
Maybe You should allow the use of the abs() function to be optional,
because if the face normal are correctly calculated (the faces are well
defined, CCW or CW) you can check the correct value, and NOT the absolute
value.
I think there are some situations in which this would create unwanted
optional lines.
Example suppose a 'kind of cylinder' with this form
---------
\ /
\ /
| |
/ \
/ \
--------
You should correctly generate vertical (concentric with the cylinder
center) optional lines, but you should NOT generate horizontal optional
lines, which I think your current algo does.
The vertical eventually will define the silhuete, but the horizontals
never will.
> A value between 45° and 22.5° should be ok.
How do you measure the angle ?
case 1:
_ _ _______face
a /
/
/face
/
case 2:
_ _ _______ face
/a
/
/face
/
> > > However, the program only check strictly
> > > adjacent facets. I have to improve it so it check also
> > > partial adjacent facets.
> >
> > I don't know exactly what you mean by partial adjacent faces, but if
> > what you mean is something like this:
> >
> > <SNIP> ...
> Yes, I meant that. Looking the STL format and your comment this
> appears to be a bug in my program. I will have a look.
1-----2
| |
3-----4-----5
| / \ |
| / \ |
6-----------7
A correct case
It's easy do make this work ok, you just have to make a match between one
triangle edge with its neighbor triangle edge, if the edge is the same
Quad = (1 3 4 2)
Try1 = (3 6 4)
Try2 = (6 7 4)
Try3 = (4 7 5)
Try1 and Quad share edge 3-4 (or 4-3, its the same)
Try1 and Try2 share edge 6-4
Try2 and Try3 share edge 4-7
If an Edge belongs to a sigle triangle then it's a
NORMAL LINE
Else /* Connects two triangles */
calc angle between the two triangles
if (angle near 0 ) /* they are coplanar */
NO LINE
elsif (angle optional test)
OPTIONAL LINE
else
NORMAL LINE
About new Ideias
You could make also an option to recreat the quads which once whore
quads, you would have to check for this, and if possible, create quads.
Rui Martins
|
|
Message has 2 Replies:
 | | Re: stl2dat conversion tool beta2
|
| (...) Then he wrote: (...) Or more simply (in LDraw-world), this: 1--2 | | | 4--5 | / | |/ | 6-----7 Leading to: 1--2 |\ | | 4--5 | / \ | |/ \| 6-----7 That was fun! Steve (25 years ago, 11-Feb-00, to lugnet.cad.dev)
| | | Re: stl2dat conversion tool beta2
|
| (...) The normal is explicitely given in STL files. (...) Yes. I have planed to optimize this point. I think it is the same case for internal cylinders. The angle must be convex and not concav. However, it is not done yet. (...) I use case 1: _ _ (...) (25 years ago, 14-Feb-00, to lugnet.cad.dev)
|
Message is in Reply To:
| | Re: stl2dat conversion tool beta2
|
| (...) No ONLY Triangles. Look for STL format description (URL) >Buy the way, do you correctly generate these lines (expecially the (...) <SNIP> (...) The program check the angle between two adjacent facets if abs(angle ) < 1e-5 No Edge if abs(angle) (...) (25 years ago, 11-Feb-00, to lugnet.cad.dev)
|
14 Messages in This Thread:
  
- Entire Thread on One Page:
- Nested:
All | Brief | Compact | Dots
Linear:
All | Brief | Compact
This Message and its Replies on One Page:
- Nested:
All | Brief | Compact | Dots
Linear:
All | Brief | Compact
|
|
|
|
