HP-GL for slice data

From: M. Burns (marshall@ennex.com) ((marshall@ennex.com))
Date: Mon Nov 25 1996 - 17:27:43 EET


On Mon, 25 Nov 1996, Delft Spline Systems wrote:
> As far as I know HPGL stands for Hewlett Packard Graphics Language,
> designed for controlling their line of 2D pen plotters, and after that
> having become the de-facto standard for pen plotters.
> So what is can do is tell a 2D plotter to plot lines, circles and to colour
> parts of the drawing.
> How can this language ever represent true (3D) surface data ?
> The only assumption I can make is that you mean to use slice data
> to represent the 3D surface in a large number of 2D sections. In contrast
> to using 3D STL files, when using HPGL the slicing will have to be done
> in the CAD-software.
> Regards
> Lex Lennings.

     This is correct. When people speak of using HP-GL as a language for
communicating to fabricators (or "RP machines"), they are speaking of
transferring slice data. The CAD program or an intermediate slice program
would take the responsibility for creating a series of HP-GL contours
from the 3-D data.
     The current configuration of the Genie fabricator runs on HP-GL. But
we have a slice program that reads StL and outputs HP-GL.
     HP-GL does have the advantages of being able to represent standard
curves, such as circles and ellipses, efficiently and without faceting.
So for these curves, it is better to get the data direct from the CAD
representation instead of through StL, which will break these curves up
into little lines. However, I am not aware of a way for HP-GL to
represent complex curves, e.g. from NURBS surfaces, directly. (If there is
a way, someone please correct me.) Because of this, I believe we will
ultimately have to do better than HP-GL.
     Comments?

Best regards,
Marshall Burns
marshall@ennex.com

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