[gdal-dev] extract vector/raster data from GeoPDF

Brent Fraser bfraser at geoanalytic.com
Thu Sep 3 09:50:37 EDT 2009


   Doing the format conversion from .ps to pdf is one thing (and there are 
several ways to do it), but embedding the georeferencing in the PDF to make it a 
GeoPDF is the interesting bit.  I haven't found any open source project capable 
of do that.  Or even capable of writing the PDF elements (e.g. Frames) necessary 
for writing the GeoPDF information.  But I remain hopeful...


Joaquim Luis wrote:
> Brent Fraser wrote:
>> 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?
> Brent,
> One only has to convert it to pdf using ghostscript.
> I did it with GMT's ps2raster, like that
> ps2raster quad.ps -Tf -A
> Joaquim Luis
>> Brent
>> Klokan Petr Přidal wrote:
>>> Hi,
>>> There is a great blog post (and the linked "worked example" post with 
>>> details):
>>> http://geopdf.blogspot.com/2009/02/geopdf-map-for-worked-example.html
>>> 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 ;-).
>>> Best,
>>> Klokan Petr Pridal
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