[gdal-dev] Confusion regarding GeoPDF composition.xml units
andreaerdna at libero.it
Mon Sep 21 23:36:25 PDT 2020
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
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 184.108.40.206 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 .
Hope this will help.
Sent from: http://osgeo-org.1560.x6.nabble.com/GDAL-Dev-f3742093.html
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