Larry
Your point is well taken. In my email -- I said "most" and hence I had the
escape hatch..but that aside...I think the topic of faceted approach raises
its ugly head again and again. Triangles are the least common denominator
for representing 3D shape and hence difficult to get away from. It is
interesting that you mention different CAD systems have the original data so
why go to faceted representation. For those of us who have dealt with IGES
files from different sources that contain free form surfaces its clear that
different Solid Modelers have different interpretation/representation of
many of the free form surfaces including blends, etc. The problem gets
complicated when translating objects from one system to another. There has
to be a translation of some sort unless we can come up with the post script
equivalent in 3D so standard print drivers can be written for the CAD
systems.
AR
>> -----Original Message-----
>> From: Blasch, Larry [mailto:LBlasch@OPW-FC.com]
>> Sent: Wednesday, November 15, 2000 1:43 PM
>> To: 'razdan@asu.edu'; rp-ml@bart.lpt.fi
>> Subject: RE: What's in a dimension?
>>
>>
>>
>> Anshuman Razdan said:
>>
>> "Manufacturing has always been happy with 2 1/2D prismatic
>> solids for the
>> most part. Free form surfaces wouldn't have gained in
>> popularity if not
>> pushed from other uses."
>>
>> I disagree completely! I have been involved in NC
>> manufacturing and RP for
>> many years, and in both, we have lived with and worked around the
>> limitations of prismatic model data and layer/toolpath contours.
>>
>> I for one, have never been happy with the results produced
>> by either NC
>> milling or layer fabrication methods. In engineering, you
>> learn to work with
>> what you have and then design improvements to get what you
>> want. All design
>> is evolutionary.
>>
>> The evolution that has always been taking place in RP and NC
>> has produced
>> dramatic changes in the capabilities of both. In NC, we
>> started with crude
>> XY coordinate control of cutter paths to rough out shapes
>> with manual depth,
>> and can now specify surface finishes on specific areas of
>> the final part
>> design within the NC software. In RP, we started with rough
>> faceted models
>> and coarse layers .0X" and can now build parts choosing
>> colors and materials
>> at .000X" layer thickness with virtually no visible facets.
>>
>> This is by no means the top of the evolutionary scale for
>> RP. The way I see
>> it, the greatest improvements in RP will come when the
>> intermediate file
>> interface is abandoned in favor of open code print drivers
>> for machine
>> control. Why do we need a new format like PLY? If the solid
>> model file
>> already contains the material/finish/color data as it does
>> in most CAD
>> systems, then why do we need to re-create that data in the
>> form of some
>> intermediate file format? I never wanted to work with a
>> faceted file in the
>> first place, but I didn't have a choice.
>>
>> Flame away.
>>
>> Larry
>>
>> Lawrence R. Blasch
>> Design Engineer
>> CAE Systems Administrator
>>
>> OPW Fueling Components
>> P.O. Box 405003
>> Cincinnati, OH 45240-5003 USA
>> Voice: (513) 870-3356
>> Fax: (513) 870-3338
>>
>> *****************************************
>> * "Always remember you're unique,*
>> * just like everyone else." *
>> *****************************************
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