[gdal-dev] Confusion regarding GeoPDF composition.xml units
nyall.dawson at gmail.com
Mon Sep 21 23:40:42 PDT 2020
On Tue, 22 Sep 2020 at 16:36, Andrea Giudiceandrea
<andreaerdna at libero.it> wrote:
> Nyall Dawson wrote
> > Actually it's a bit more complex than this, because regardless of the
> > DPI specified for the page, the width/height have to be specified in
> > size in inches * 72! (i.e. there's a hardcoded 72 dpi assumption
> > somewhere).
> I don't know how composition.xml works, but if you wonder why in PDF page
> the width/height have to be specified in "size in inches * 72" you will find
> a hint in PDF 32000-1:2008  especially at paragraphs 18.104.22.168 Page
> Objects, Table 30 and 8.3 Coordinate Systems.
> "The length of a unit along both the x and y axes is set by the UserUnit
> entry (PDF 1.6) in the page dictionary (see Table 30). If that entry is not
> present or supported, the default value of 1⁄72 inch is used. This
> coordinate system is called default user space"
> "Note 2: The default for the size of the unit in default user space (1⁄72
> inch) is approximately the same as a point, a unit widely used in the
> printing industry. It is not exactly the same, however; there is no
> universal definition of a point."
> "UserUnit: A positive number that shall give the size of default user space
> units, in multiples of 1⁄72 inch. The range of supported values shall be
> implementation-dependent. Default value: 1.0 (user space unit is 1⁄72
> See also  and .
So then my question would be why the PDFs attached to
https://github.com/qgis/QGIS/issues/33465 are showing incorrect page
sizes in Acrobat Reader, when it appears as though GDAL is correctly
Have you any ideas why this could be occurring?
> Hope this will help.
> Best regards.
> Andrea Giudiceandrea
>  https://stackoverflow.com/a/21164534/8779560
>  https://github.com/qgis/QGIS/issues/33465#issuecomment-644566633
> Sent from: http://osgeo-org.1560.x6.nabble.com/GDAL-Dev-f3742093.html
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