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Slight size changes from ArcGIS to Illustrator

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#1
danielle

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My text is changing size, and strokes are changing widths!

Maybe this has been discussed already and I missed it. Before I start doing a lot of testing, I thought I would check in here with you knowledgeable folks.

I am using ArcGIS 9 and exporting to Illustrator 10. I have noticed that the sizes of text and strokes change slightly. For example, text that is Arial 8pt in ArcGIS becomes 7.92pt in Illustrator. A line stroke that is 0.4pt in ArcGIS becomes 0.48pt in Illustrator.

This has been an issue when a client says they want their labels a certain size, and they have to be re-adjusted.

Does anyone know if the change is happening on the ArcGIS or the Illustrator side? Do newer versions of Illustrator behave the same way?

I did a quick test and drew a 1 inch by 1 inch square in an ArcGIS layout. Exported to Illustrator, this size was the correct 1 inch by 1 inch. However, when the units are changed to display in points, you get 72.001 wide by 71.996 high.

Are these discrepancies caused by rounding errors, or is there a difference between pixels and points? Am I missing something?

-Danielle

#2
ELeFevre

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I believe it happens on the Illustrator side. I say this because the same resizing occurs when you take an Excel table and paste it directly into Illustrator. The font size will always be slightly smaller. I'm hoping someone has a good explanation for why this happens.



#3
merft

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Your encountering rounding issues and are known issues within ArcGIS due to the development environment they use. One of the more common issues seen were the moving scale bar and north arrow. As it was explained to me by ESRI, not all the compiler libraries are optimized for double-precision math and rounding errors appear particularly in layout and printing. For the most part, these are unperceptible in a final print/plot but can be seen if imported into other applications.

#4
MichaelG

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My text is changing size, and strokes are changing widths!


Are these discrepancies caused by rounding errors, or is there a difference between pixels and points? Am I missing something?

-Danielle


Danielle,

Yes, these are rounding errors. You can minimize them by setting the ArcMap export resolution to a value divisible by 72 (eg. 288 dpi, 360 dpi). The ESRI support website has a technical article summarizing this issue:

Problem: Line widths or text sizes are incorrect in ArcMap created AI files
http://support.esri....l...how&d=29706

Sincerely,

Michael G.
ESRI
Michael Grossman
ESRI

#5
byzantium

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I believe there is another issue which could affect some maps (perhaps really large maps more than others) transferred this way: relatively low precision in Illustrator coordinates. I think Illustrator's coordinates are not some sort of super double long floating point number but instead based on standards defined in the late 1980's for PostScript. I believe this is a factor in why the artboard has not expanded beyond 227 inches (or 16383 points). If AI coordinates are limited to 8 bytes, then there's the potential for rounding to affect a number of things.

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