Re[2]: New STL format

Date: Tue Jun 02 1998 - 14:45:36 EEST

     I don't want to eliminate the 3d model as the interface to the RP
     machines, I want to more fully define the objects I wish to build. The
     current STL format is a crude surface representation of the intended
     geometry that was more than adequate 10 years ago. Times change. The
     resolution of the STL file is governed by how close you wish to
     "approximate" the smooth surface. It's still an approximation so why
     not get the info strait from the source?
     Postscript is a language that tels the printer what the document
     should look like, not how to create it. Why are we forced to tell the
     machines how it should be done.
     Larry Blasch

______________________________ Reply Separator _________________________________
Subject: Re: New STL format
Author: Bert VandenBerg <> at internet
Date: 6/2/98 1:05 PM

Why to keep a 3D model as the interface to the RP machines:
- One might imagine that future RP machines might not build the part
layer by layer.
- defining the slope of the surface in the build direction is ambiguous
when given only
  a layer specification
- we might need a separate post-processor for each machine to take
advantage of special machine capabilities. This becomes a support
problem for the CAD developers and the machine
- conceptually the slice approach brings us closer to NC code, which is
a specification of what the machine should do, rather than a just a
description of requirements (3D shape). This makes it difficult to get
the same part made by different types/sizes of machines.
I'd prefer seeing a better 3D model description, with associated process
information (tolerances, material specifications, build parameters,
inspection requirements, hand finishing). This territory seems to be
claimed by advocates of STEP. STEP has 3 methods
for defining shapes:
- Boundary representation (NURBS etc. used by solid modelling CAD
- construction solid geometry (shapes defined by combinations of blocks,
cones, spheres etc.)
- facetted boundary representation (e.g. triangle mesh)
STEP also has intentions to map manufacturing process information.
Unfortunately, only the first representation is currently supported by
major CAD vendors, and the STEP process is
pretty slow.
just my 2 cents,
 bert wrote:
> To list,
> Albert Young said: Basically, we began with the HPGL language
> utilizing such commands as X, Y, Z, pin-up,
> pin-down, and speed, and then we added line
> pattern.
> A question for Albert: HPGL1 or HPGL2?
> Concerning a new STL format, To my knowledge, every 3D CAD system,
> surface modeler and solid modeling system can output an HPGL or
> PostScript format plot file and most if not all can produce an
> accurate slice or cross section through the object or objects in
> native format. Most of these same programs can support the
> color/texture information used in photorealistic rendering. So...Why
> not use the CAD/Sculpt/Modeler program to create the data set for the
> machines to follow instead of re-inventing the wheel?
> As the "layer thickness" of many of the current machines gets smaller,
> the need for extra information in the build file is being eliminated.
> Near flat and flat triangles become meaningless if there is uniformity
> in the fill/hatch and overlap in the boundry trace, so why not just
> define the boundry only.
> The data defining the fill/hatch should be a constant (material
> specific table) within the machine that is called for by the boundry
> conditions of that layer. (Different material properties from the same
> resin for each part?)
> The photorealistic attributes of the object could then be mapped to
> the slice/section as the slice is generated, and either added during
> the build by a secondary coloration process or by means of resin
> material science (dyes sensitive to threshhold levels of energy or
> frequency could be in the resins).
> The result is that the triangle approximation of the contoured surface
> is eliminated and you are working with the model in native format so
> design changes re-use the existing data sets.
> What am I missing? The model accuracy (shape, color, texture,...) is
> now a function of the design software. The machines that produce the
> parts are then just like the 2d printers of today, if all you want is
> black and white at 200dpi, that's what you buy. If you want high speed
> realistic color output you pay more and buy a faster/higher resolution
> machine.
> Sincerely,
> Larry Blasch
> System Administrator for Engineering Services
> OPW Fueling Components
> P.O. Box 405003
> Cincinnati, OH 45240-5003 USA
> Voice: (513) 870-3356
> Fax: (513) 870-3338
> **********************************************************************
> Disclaimer...The views expressed are personal opinion and not those of
> OPW Fueling Components.
> **********************************************************************
> * "Always remember you're unique, just like everyone else." *
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> For more information about the rp-ml, see

Bert van den Berg                   E-mail: 
Hymarc Ltd.                  
35 Antares Drive                        Tel: (613) 727-1584 
Ottawa, Ontario  K2E 8B1                Fax: (613) 727-0441
For more information about the rp-ml, see

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