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Using PDF reDirect
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Topic: AutoCAD LT question Post Reply Post New Topic
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Joined: 03 Aug 06
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Quote john.breen Replybullet Topic: AutoCAD LT question
    Posted: 03 Aug 06 at 3:51PM
In trying to output diagrams from AutoCAD LT 2002 to PDF, I have had next to no problems (outstanding software, btw). But in trying to output solid-hatched areas, I am getting the following effect:

...where the gray roadway has streaks. My understanding is that LT does not treat solid hatching as true solids, but instead creates a very dense hatch pattern. Printing to a plotter or crayon (solid ink) printer does not cause this effect. I expect the solution lies within ACAD more than PDF reDirect. Any suggestions?

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Quote Michel_K17 Replybullet Posted: 03 Aug 06 at 4:59PM
Hello John,

   You have described the problem very well. And you are correct: there is nothing that can be done on the PDF reDirect as it creates the PDF output as specified by ACAD.

   The problem really stems in the differences between how the way the human eye perceives the output on physical paper vs the way it is displayed on the screen.
  • On Paper: the resolution of the printer is typically 300 dpi or higher. The hatch pattern is so small that the human eye will have difficulty in discerning such a small cross-hatch and will appear as a shade of grey.
  • On the Screen - when zoomed out: you are at the mercy of the PDF Reader, and how it decides to display the hatch pattern. However, they will typically take the discrete pixels and display those and omit others in a semi-random fashion. As a result, you have what looks like random lines or dots.
  • On the screen - Zoomed Way In: By zooming in (in the Reader, you can zoom in much closer to the paper then you could with the naked eye), you can clearly see the hatch pattern which is causing the problem.

   Personnally, I do not like these hatched patterns as they can create PDF files to be much larger than they need to be as each line of the pattern in an additional "object" in the PDF file.

   There is a similar problem with transparencies. Although the PDF specification supports transparent objects, physical printers do not. Therefore, the internediate Postscript file created by the Postscript printer will convert objects to a bitmap with "holes" to approximate a transparent object. Once again, this creates artifacts in the PDF file that are objectionable, and makes the PDF larger than it needs to be.
   A solution may the PDF Reader itself. Check the "Page Display" preferences in the latest PDF Reader v7. There are options to:
  • Smooth Text
  • Smooth Line Art
  • Smooth Images

   You might find that turning the second one ON or OFF may improve how it appears in the Reader.


Edited by Michel_K17
Michel Korwin-Szymanowski
EXP Systems LLC
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