Collaborating in geospatial context since 2000!

Wednesday, February 11, 2009

Why Two GeoPDF Specs?

An anonymous reader asked

I'm not sure that the community needs two specs. What am I missing?

This is a hot question, but I hope I can cool it off a bit. The community doesn't need two georegistration techniques, I suppose, but it does have two, so as software providers we need to deal with it. And that's only for PDF. How many ways can you georeference, say a TIFF file? Well, there's world file, at least three different combos of GeoTIFF tags, different metadata payloads cooked up by GIS vendor X, etc. DGN? DWG? DOC? XPS? FOO?

What TerraGo has done with releasing the georegistration technique it used to create and have had created hundreds of thousands of GeoPDF files is to document what we did. This is why it will be published as a best practice rather than a OGC-endorsed specification. People have invested heavily in GeoPDF map libraries that use that technique and we're going to make sure that investment is protected. Similarly, GeoPDF files can be created using the extensions that Adobe has cooked up. We can deal with that, too. Ultimately, I hope that the people who ultimately use, enjoy, and profit from GeoPDF maps and imagery neither know nor care about the details of the arrangement of the bits and bytes that make the georegistration -- just rest easy in knowing that GeoPDF is built on open standards.

If you really get down into the details of how the two techniques differ, there are some contexts which one might be preferable to the other -- and vice versa. Neither is fully baked, IMO, so there will be extensions and revisions. However, GeoPDF's situation is much more akin to GeoTIFF's than a VHS v. Betamax. It's more a matter of flavor than variety. From my perspective, both flavors are delicious. From a GeoPDF user's perspective, it all should "just work".

I will be delving into the details of both techniques in subsequent posts.


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