[gdal-dev] extract vector/raster data from GeoPDF
bfraser at geoanalytic.com
Wed Sep 2 11:46:19 EDT 2009
I see the example calculation of the transformation matrix, and a statement "I
created a GeoPDF by running the Postscript file through Ghostscript to create a
Postscript file that looks like this"
But I don't see where the georeferencing is written into PDF to make it a
GeoPDF. Is it a Ghostscript command line?
Klokan Petr Přidal wrote:
> There is a great blog post (and the linked "worked example" post with details):
> It shows you how to create geopdf via GhostScript - so there is
> already a practical open-source example how to encode the georeference
> into the PDF/PS according the OGC standard - for use in Acrobat
> Reader. To add support for such tag in MapServer, which generates pdf
> dynamicaly via pdflib, should not be totally problematic.
> Decoding is not as hard either, there are nice libraries like poppler
> (http://poppler.freedesktop.org/), which allows you to parse vectors
> (and convert them to SVG for example) or rasterize the PDF files (into
> TIFF,...) via Cairo.
> The work is in assigning correct geographic coordinates to the
> coordinate system internally used in PDF files and especially write
> the bridge to the outside world (with GDAL/OGR).
> I am afraid that authors of the GeoPDF standard would not like this,
> as it seems that the idea of GeoPDF is "see it in the Acrobat, print
> it, but that's all". At least I think so, because they discontinued
> their Geopdf2geotiff product and all the conversion tools are just one
> way - into GeoPDF. Please correct me...
> Anyway, in this moment you can quite easily use utility like
> "pdfimages" to extract full quality image tiles from any GeoPDF (like
> those from USGS) and merge it based on their location in PDF into one
> GDAL file via VRT (gdalbuildvrt) with a bit of hacking. This is what I
> did for my favorite USGS DRG of Grand Canyon ;-).
> Look at: http://klokan.mzk.cz/~klokan/geopdf/ - soon I will update the
> MapTiler.org overlay examples...
> Unfortunately all PDF parsing libraries I know are GPL, and that means
> we can't use them for the gdal driver - because of the license issues.
> But to create a GPL utility for converting GeoPDF to anything what
> GDAL/OGR supports should be OK. Poppler can be the best base of such
> GDAL-based utility for reading/rasterizing of the GeoPDF files.
> Now just find a sponsor and time to make it ;-).
> Klokan Petr Pridal
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