Re: [CAD_CAM_EDM_DRO] digitized elevation grid to STL code & Windoze.exe software released for free....

Michael Milligan wrote:

>
> Doug
>
> I have recently been asked about the Import of .STL
> files into Dolphin but so far have been unable to find
> any information about .STL through our UK sources.
> I would appreciate some initial information on these files :-
>
> What is an STL file?

STL is short for either 'Surface Triangulated Layer' or
'STero Lithography'.

I think the former is a better description. A surface can
be 'decimated' (decomposed and approximated) into a surface
composed of lots of little triangles. The more triangles,
the more accurate the rendition, but also bigger data sets
and longer rendering and processing times (ie twice the
resolution, 8 times the data because of the cube law in X,Y&Z).

> Is the format defined somewhere.

Yes, a brief overview:

There is an ascii version, and a binary version. The binary
version has fewer bytes to hold the same amount of information,
and therefore the binary version is to be preferred.

Each format contains the XYZ coordinates of each vertex
of each triangle. The normals (the vector direction
perpendicular to the plane of the triangle) are also
given.

http://www.vr.clemson.edu/rp/rp_stlfile.htm gives the
following as an ascii example:

solid sample.stl created by Wei Feng on 15th OCT. 1994
facet normal -1.000000 0.000000 0.000000
outer loop
vertex 140.502634 233.993075 -38.310362
vertex 140.502634 229.424780 -38.359042
vertex 140.502634 242.525774 -27.097848
endloop
endfacet
facet normal 0.903689 0.004563 0.428166
outerloop
vertex 134.521310 273.427873 30.342009
vertex 134.521310 308.505852 30.715799
vertex 140.502634 334.576026 18.369396
endloop
endfacet
facet normal -0.903689 0.004563 0.428166
outer loop
vertex 140.502634 334.576026 18.369396
vertex 140.502634 294.929752 17.946926
vertex 134.521310 273.427873 30.342009
endloop
endfacet
... ...
endsolid sample.stl

and he (Dr. Wei Feng of Clemson University, Center for Advanced
Manufacturing) gives the following explanation of the binary format:

BINARY STL file format is accessed by byte. The format is as follows:
the first 80 bytes are used for description, and the next 4 bytes
represents the total number of the facets(Long Int), followed by
the facet information (normal and 3 vertices), the normal and vertices
are stored in floating point format, each occupying 4 bytes. At the
end of each facet information section, there are two bytes spaces, then
the next facet is repeated till the end of the file. When BINARY format
is used to describe STL file, the data size is much smaller than ASCII
format, so most STL files available now use BINARY format.

<BINARY STL file format>::=<STL file entity name><facet number
N><facet info>
<STL file entity name >::=<80 bytes entity name, spaces are used to
fill the blank>
<facet number N>::=<4 bytes long integer>
<facet info>::=<facet normal><facet vertices><2 bytes spaces><facet
normal ><facet vertices><2 bytes spaces> ... ...
<facet normal>::=<lx,ly,lz, float, 12 bytes>
<facet vertex coordinates>::=<x1,y1,z1,x2,y2,z2,x3,y3,z3, float, 36
bytes>

---------------------------

> Is it a proprietary file format or a general standard format.

I believe it is an open standard.

> What software produces STL files.

Probably most CAD files. Many graphics modelling programs (Rhino,
Maya).

After you produce a file, you might want to look at it.
Might I humbly suggest the fabulous '3D Explorer' by
http://www.xdsoft.com
(now http://www.us.righthemisphere.com/products/3dexplore/index.htm )
which can display and rotate (using OpenGL accelerator video cards)
and even translate, not only STL files but also every other imaginable
file (I noticed today, even GCode!!!! but I haven't tried the latest
version with that feature yet). Works for 30 days free, then you have
to pony up $49. A bargain. Actually, I think this is the best Windoze
program ever written, but I diverge.....

After you look at it, you might want to generate some gcode by importing
the STL into VectorCAD/CAM, MillWizard, or Deskproto (or Deskproto
Lite).

> Thanking you in advance
> Michael

My pleasure.

Doug Fortune
http://www.cncKITS.com