# Re: Understanding the eps bounding box (rounding)

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Am 02.03.2018 um 09:16 schrieb Andrew Bernard:
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```Hi Urs,

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Forgive me if saying something you know, but just confirming that PostScript user space coordinate units are 1/72 inch. This is close to one point, but there is no universally accepted definition of one point. Some conventions use 1/72.72 inches (!), for example.
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OK, thank you. Although I was aware of that issue it seems I'll have to review the calculations.
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So what you're saying is that when the EPS bounding box says "80" this means "80 times 1/72 inch", right?
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According to https://tex.stackexchange.com/questions/8260/what-are-the-various-units-ex-em-in-pt-bp-dd-pc-expressed-in-mm#8337
```- 1pt in LaTeX is 1/72.26999 inches.
- 1pb is 1/72.00082 inches. ("bp" refers to Big Points)

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According to http://lilypond.org/doc/v2.19/Documentation/notation/distances-and-measurements
```a LilyPond \pt is 1/72.27 inch, so obviously the LaTeX variant.

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So obviously I do have to perform some transformations since my current assumption (the units in the bbox are equivalent to pt) produces slight offsets. But still I have to afterwards deal with the (annoying) issue that the bounding box is truncated to integers.
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The information confirming this is on p 183 of the 3rd edition Postscript manual (same as the one Karl quotes from). [That manual is freely downloadable from Adobe.]
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I don't know what 'bp' is, sorry, and I don't know what the size of a point ]\pt in LaTex is either.
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I don't know if lilypond transforms Postscript user space coordinates into device space coordinates or when it does that. I thought GS would handle that late on, closer to final imaging.
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Does anyone know at which stage this bounding box is calculated for the first time? And if there's any possibility to access that information from within LilyPond to write out a special logfile? This would be very interesting for another reason: I would actually like to determint the amount of protrusion *to the right* too, and that is not possible for ragged systems. The lower left corner is relative to the beginning of the staff symbol, so I will always know how much space is used to the left of that. But I can only infer the *right* protrusion from the difference between the upper right corner of the bounding box and the line width (which I know). When the system is justified this gives correct results but not when the system is ragged.
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But maybe that's a separate question.

Best
Urs

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Andrew

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On 2 March 2018 at 18:26, Urs Liska <li...@openlilylib.org <mailto:li...@openlilylib.org>> wrote:
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I think it *is* the smallest box, but truncated to integers. At
least I can't imagine a box that leaves full units empty.
From what I've seen so far I was confident that the numbers
correspond to what LilyPond sees as \pt, and also in LaTeX I have
treated the numbers as pt (as opposed to bp).

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