Re: [rp-ml] A QUERY ON STL FILE FORMAT

Some software have a problems (on surface)when converted CAD to stl file.

Charles Overy wrote:

> Ahmed,
>
> You first question deals with the area of mesh processing and mesh geometry.
> Do not limit yourself to stl as this is only one format of a mesh
> description and a mesh is only one method of geometry description.
>
> You say "The images will be developed in AutoCAD or any CAD software, then
> exported as STL file. There are some huge assumptions going on there that
> stl files created from various CAD programs are similar. Some CAD programs
> take a strict approach to stl exprt and will only generate a mesh if the
> underlying geometry is a solid. Unless AutoCad has changed recently, it
> only alows export of a single solid using the stl export command. This is
> pretty limiting if you are doing more artistic work where there is no
> underlying reason to use a solid modeler. Also, will you engrave interior
> geometry or only the surface information? How will you eliminate the
> interior geometry if it exists?
>
> Indeed, it is not clear at all to me why you would necessarily use a mesh
> if you are going to be blasting a voxel. Why not use a voxel processing
> algorithm from the start. Import your geometry, voxelize it at the
> resolution of your device, select the voxels to blast and then selet
> coordinates of the voxels in some stepwise pattern. It will not be as fast
> as some clever "nearest neighbor" type of route selection but it will be a
> lot easier to program.
>
> Just a thought
>
> Charles Overy
> LGM
>
> -----Original Message-----
> From: owner-rp-ml@rapid.lpt.fi [mailto:owner-rp-ml@rapid.lpt.fi]On Behalf
> Of Ahmed Issa
> Sent: Monday, April 26, 2004 10:33 PM
> To: rp-ml@rapid.lpt.fi
> Subject: [rp-ml] A QUERY ON STL FILE FORMAT
>
> Hi All,
>
> I am developing a laser marking system, which is supposed to produce 3D
> images inside a cubic bulk of glass. I am sure that some of you have seen
> this kind of souvenirs in the market. . I am going to develop a code to
> handle the STL file and convert it into (X, Y, Z) points that resemble the
> 3D shape. The laser beam will be focused within the work piece at the
> specific coordinates, thus allowing it to internally vaporize a spot of the
> material leaving a hollow spherical spot (VOXEL in the order of micons) in a
> phenomenon known as micro-fabrication or internal marking. The voxels are
> not connected, however so close so that they form a 3D image. As I
> understand, this process falls under Steriolithography (please correct me if
> mistaken in categorizing the process).
>
> The problem I am facing with STL file format that it randomly sorts the
> facets. I can have control over some parameters such as the resolution of
> facets but some shapes are not properly tessellated (i.e. big triangles such
> as the case of cubic shapes).
>
> My question is: does any one know good reference books or websites on this
> technique, specifically on how to manipulate STL files. Also on sorting the
> points in space so as to optimize the travel distance of the XYZ positioning
> bed?
>
> Any hints or useful information will be highly appreciated, thanks.
>
> Ahmed Issa.
>
> ----------------------------------------------------------------------------
Received on Thu Apr 29 06:25:56 2004