A previous thread http://lists.osgeo.org/pipermail/gdal-dev/2015-May/041727.html discussed the effect of the DPI parameter of the geospatial PDF driver, one response being
"It may be that DPI setting at the moment does not have a totally desired effect. It would feel natural that increasing DPI from the default value 72 into a bigger value like 300 would make the page size of the PDF smaller expressed as physical units like millimeters." I stumbled upon this issue because previously I'd been creating PDFs using ImageMagick "convert". I needed to produce page-size printed maps of an image with having much greater resolution than Adobe's "standard" 72 dpi so used the convert "-page" option - whereupon letter-sized prints were automatically generated when printed using Adobe Reader. [Without that option the same result could be obtained by selecting Adobe Reader's "Fit to Printable Area" Page Scaling option - but this file will be printed by others less knowledgeable than I so I wanted to have one less thing for them to mess up.] When I decided to create geospatial PDFs using GDAL, the default gave a file which again required setting "Fit to Printable Area" - so I looked for a way of avoiding that. Using the "DPI" option seemed the obvious answer, but altering it did not have the expected effect - "Fit to Printable Area" was still required, as previously found by the poster of the previous thread. Delving into the PDF file itself, I see the "DPI" option changes not only the PDF "MediaBox" variable but also its "UserUnit" variable, such that the printable size is unchanged. To me that makes no sense, since printing of a PDF is common and in many cases one wants to print an image at a much higher resolution than 72 dpi. I do understand the need to limit the size of "MediaBox" and the use of "DPI" to reduce the "MediaBox" values. I note that when I use IM's convert -print option it _also_ reduces the size of "MediaBox" - but it did _not_ change "UserUnit", hence the expected letter-size printed page is produced by IM. So I'd urge you to also not change the PDF's "UserUnit" when driver option "DPI" is invoked - that would help those wanting to print higher-resolution images. I personally don't know of a reason why "UserUnit" needs to be changed. Jack Glendening PS: personally I have a work-around - after PDF creation within a script, a command-line editor removes the "UserUnit" parameter from the PDF. But it's kludgey and I think the problem would be better addressed through the "DPI" driver option. _______________________________________________ gdal-dev mailing list [email protected] http://lists.osgeo.org/mailman/listinfo/gdal-dev
