[gdal-dev] Some info about geospatial PDF and TerraGo Toolbar

[George Demmy]

Here's some info that might help the development effort for PDF and
use of PDF created or georegistered by GDAL.

Something that is confusing is TerraGo Toolbar's behavior with PDF
files not created by TerraGo software. The company policy was to not
support files with the Toolbar, the reason being the company could not
afford to support debugging of files created by other software
systems, etc., with a free product. This policy was imperfectly
implemented in Toolbar code: sometimes it can be tricked into
believing a PDF was created by TerraGo even when it wasn't. Some of
the "works sometimes, other times not" behavior can be attributed to
this, especially when it comes to ISO encodings which have been
supported since 2008. Fortunately, this policy has been abandoned and
the next release of the Toolbar will attempt to read any and provide
display of coordinates, measurement, etc. Toolbar is due to ship later
this month. That will have some rudimentary introspection tools to
help figure out why a PDF doesn't seem to work.

Some of the issues reported in an earlier thread may be related to the
Toolbar "refusing" to display the coordinates and might not any
indication that the encoding has been bunged, strings not properly
formed, etc. As was noted in the earlier thread and as I've confirmed
with some prerelease Toolbar code, the encodings are correct for both
samples cited, so good job Even!

With the OGC encoding, it's safer to always write the numbers as
strings .16g. However, the ISO method does not permit this. The ISO
method is less sensitive to the limitations of the PDF real number
object type, so the only concern there is precision (PDF reals are ~ 5
significant digits in the fractional part (cf. ISO32000)), which
cannot be addressed without modifying the encoding specification and
everything that implies.

When did gdal_translate pick up the cool macho supremo ability to
georegister a PDF? The googles did not help me...

I fell off this list a while back, but am back on. LMK if there are
other questions.

HTH and cheers!

George Demmy