[gdal-dev] GeoPDF (TM) vs. GeoSpatial PDF

[George Demmy]

On Mon, Jun 4, 2012 at 5:02 AM, David Strip <gdal at stripfamily.net> wrote:
> On 6/3/2012 10:59 AM, George Demmy wrote:
>
>>> David Strip wrote:
>
>
>>> >  When used in conjunction with the (free) TerraGo toolbar, the geoPDF
>>> >  provides many more capabilities than a geo-spatial pdf, especially if
>>> > the
>>> >  pdf "modify" permission is set.
>>
>> As of version 6 which shipped recently, the TerraGo Toolbar offers
>> continuous display of coordinates and other functionality for any
>> geospatial PDF as long as it can grok the encoding. It supports OGC
>> and ISO and uses proj4 via GDAL under the hood for projections. Like
>> Reader, Toolbar has some more advanced functionality that is
>> accessible if certain permission bits are set.
>>
> While V6 of the toolbar (and in fact previous versions) provide continuous
> display of coordinates, a "true geoPDF" (which I believe means having the
> LGIDict), has far more coordinate conversion capability, as well as the
> ability to add "geo-marks", geo-located stamps (icons) added to the file. I
> verified this by downloading the latest version of the Terrago Toolbar
> (15.0.0.591). I opened a geo-spatial pdf that I created with ArcMap 10.0.2.
> I can get the position display in Lat/Lon and MGRS at the bottom of the
> image, and in the Geolocator tool (from the toolbar), I can also see UTM13N,
> WGS84, USNG, and MGRS. I can't use the GeoMark tools at all. I then open a
> geoPDF (a new generation USGS topo map). In this case I can set the
> GeoLocator projection to display in any of a hundred or more predefined
> projections, or define my own projection parameters. I can also mark the map
> with GeoMarks. The ability to use GeoMarks is not a function of the pdf
> "modify" bit being set. It is set in the ArcMap generated map, which I can
> add non-geospatial marks with other pdf tools.

To mark up a PDF in Adobe Reader, the file must be "enabled for
comment and analysis" by Adobe software. This has changed a little in
Reader 10 which allows use of the note tool for any PDF where previous
versions did not. You can mark up any non-secured PDF in Acrobat and
perhaps other software as well. To use the GeoMark Toolbar, the file
must be both enabled for comment and analysis (Adobe) and
GeoMark-enabled (TerraGo) to mark it up in Reader. It need only be
GeoMark-enabled to be marked up in Acrobat with Toolbar. The ability
to use GeoMarks in Adobe Reader *is* the function of a functionality
access bit being set by Adobe as well as TerraGo. However, it's not
permission to modify the file as much as permission/license to use
software tools. ArcMap does not generate comment-enabled PDFs by
default, so I don't understand what you mean in that last sentence.

> I belief that the presence of the LGIDict is what enables these other
> features, but I could be wrong.  That's something I've been trying to find
> out.

All the presence of an LGIDict guarantees is that someone has tried to
use the OGC encoding to georeference the PDF. The different
functionality is turned on by permission bits, although Toolbar looks
for signatures which indicate that a map was created by very old
TerraGo software, and the presence of LGIDict is part of that
signature. It's possible to cook up a PDF with an LGIDict that will
trick Toolbar into working. I hope that leaves nothing to figure out
with respect to this stuff.

Regards,

George