[poppler] Supporting PDF 1.6 UserUnit

[Leonard Rosenthol]

At 08:04 AM 7/11/2005, Brad Hards wrote:
>If the cropbox is 3600 x 7200, then with  the default (72) it would be 50 x
>100 inches, but UserUnit 2 represents a "drawable" area of 100 inches x 200
>inches?

         Correct.


> >          It is only currently generated by the Visio & AutoCAD
> > PDFMakers when the output is larger than 32Kx32K.
>OK, so it represents a user space that is nominally larger than 444 
>inches (10
>metres) each side. Probably we'll be drawing that scaled anyway...

         Exactly!


> From I see it changes the size of the cropbox, and the dimensions of
>everything within it. Now the change to the size of the cropbox in user space
>will that should be reflected in a change to the transformation to the device
>space (since presumably we'll be scaling).

         Correct.  If you scale both the drawable area (eg. cropbox) 
AND apply the same scale as the base transform to the contents, then 
you should have the correct result in the final output.


>So if an object would have been drawn 100 units x 50 units on a cropbox that
>is 150 units x 100 units, then setting UserUnit = 3 will produce an object
>that is 3 times bigger on a cropbox that is 3 times bigger. For any fixed
>transform from userspace to device space, the output will be 3 times bigger.

         Correct.


>If when we render it onto a physical sheet with a "fit to page" scaling, it
>will be the same size though.

         Correct, HOWEVER, in this case, to do things "properly", you 
really need to "double scale" - once up to the UserUnit and the back 
down to "fit to page"...


>So the only case where it matters is for things like engineering drawings,
>where if the original sheet is A1, then if we print at "100%" but don't take
>into account a UserUnit not equal to 1, then we can render (and print) the
>drawing at the wrong size.

         Bingo!


Leonard

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Leonard Rosenthol                            <mailto:leonardr at pdfsages.com>
Chief Technical Officer                      <http://www.pdfsages.com>
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