[gdal-dev] geospatialPDF DPI and EXTRA_IMAGES

[Even Rouault]

Le mardi 19 mai 2015 10:12:46, Luca Delucchi a écrit :
> Hi devs,
> 
> I noticed something strange about the position of EXTRA_IMAGES with
> different DPI values.
> 
> If I set a value lower than 73 the  EXTRA_IMAGE it is added in the
> right place, but If I increase the value the EXTRA_IMAGE it is moved
> up from the correct point.
> 
> Is this normal or a bug?
> Is there any way to avoid this shift from the correct position?

Luca,

According to the doc, "x and y are in user units from the lower left corner of 
the page"

If you set a DPI < 72, GDAL will correct it to DPI = 72 since AFAIR, this is 
the minimum accepted value by the PDF spec (not sure of that though).

And since 1 user unit  = DPI / 72, if you increase the DPI, you must divide 
the offset by DPI / 72 so that the image stays at the same location in term of 
pixels.

From the PDF spec:
"""UserUnit
number
(Optional; PDF 1.6) A positive number giving the size of default user space 
units, in multiples of 1 ⁄ 72 inch. The range of supported values is 
implementation-dependent; see implementation note 177 in Appendix H.
Default value: 1.0 (user unit is 1 ⁄ 72 inch).
"""

Even

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