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Re: Lost Line Directives in 3D Graphics

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  • Subject: [mg30169] Re: Lost Line Directives in 3D Graphics
  • From: Tom Burton <tburton at>
  • Date: Wed, 1 Aug 2001 02:19:24 -0400 (EDT)
  • References: <9k2d95$2ds$>
  • Sender: owner-wri-mathgroup at


On Mon, 30 Jul 2001 01:29:09 +0000 (UTC), in comp.soft-sys.math.mathematica you wrote:

>Dear MathGroup,
>Here is a case where it appears that Mathematica incorrectly renders the
>postscript code for Graphics3D. I wonder if other people obtain the same
>effect that I obtain.

>The plot consists of a long thin black line, and a shorter thick red line on
>top of it, with a three polygon cone at the end, but slightly detached from
>the short line. The line directives for the short line are lost, so that it
>also appears thin and black.

I tried this with version 4.1.0 for Windows (11/2/2000) on Windows NT 4 service pack 6. I may be seeing the same thing you do, but I interpret it differently. The short line is not different in some frames; rather, it is entirely suppressed.

When two lines coincide in a 3D graphic, the choice of which to display is undefined and therefore, I assume here, subject to the vagaries of numerical round-off accidents. So when I see that, sometimes the thick line is suppressed by the thin line and sometimes not, I am not surprised.

As far as the presence or absense of the polygon is concerned, once I get into the realm of round-off accidents, all bets are off.

I suggest that either you shorten the shorten the thin black line to keep it away from the thik red line.

Tom Burton

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