Collaborating in geospatial context since 2000!

Tuesday, May 05, 2009

History of GeoPDF: PDF Map Books, LGIView, and LGIDict

GeoPDF has a history that goes back to the 1990s. Using PDF files for engineering applications was the brainchild of Phil Lee, one of the founders of TerraGo. In 1999, Phil, then vice president of Layton Graphics, bid on a project to deliver maps and engineering drawings to telecommunications maintenance crews. The maps and drawings came from scanned paper maps, AutoCAD and Microstation design files and backed by different database systems maintained by different engineering groups. Phil was an avid Acrobat user -- fanatic may not be too strong a word. He knew more about getting stuff done with Acrobat than anyone I knew then or since. Taking all of these heterogeneous formats and data to PDF and exploiting the features of PDF and Acrobat was obvious to him. The PDF solution was compelling because it was not tied to any CAD or database system, secure, and easy-to-use. The solution was to render all of the engineering data to PDF, add bookmarks and hyperlinks to ease navigation, and organize the resulting map book with an interactive index map. My nominal role in all of this was for the rendering AutoCAD DWG files to PDF, along with extraction and analysis of the data that they contained for creating links and metadata. Alan Stewart headed up the Microstation side of things. Alan had been writing software to manipulate and render DGN files for quite a while. He arrived at Layton Graphics with Michael Bufkin some years before in an acquisition of Michael's company Cad Share. Michael ran Layton Graphics' engineering group. Michael, Alan, and I are all still working together at TerraGo.

The PDF map book project was a big success for Layton Graphics. We delivered the first map book set in the fall of 2000 and last in 2005. We built a custom system that consumed the raw design files and databases and churned out 2500 map book updates quarterly, burned them to CD and delivered them to the different maintenance groups. These map books were popular with the crews, and soon received requests for new features. These features were usually exposed by creating plugins to Acrobat. This was the responsibility of JB Freels. It was increasingly obvious that a combination of software and carefully prepared data was a compelling application that could be used in numerous contexts. It seemed that everyone we showed our map books to wanted them.

One of the first attempts to productize a collection of PDF files specifically configured for engineering applications along with Acrobat plugins was called LGIView. Adobe profiled LGIView as a success story. Patrick Graves was brought on board in 2002 to serve as chief software architect and run the software development group. One of the LGIView features was a coordinate finder. Engineering design coordinate systems are almost invariably Cartesian, but they are sometimes aligned with some mapping coordinate system like UTM or a State Plane system. Since the working coordinates were Cartesian, it was a simple matter to embed a rotation, scale, and translation that mapped the engineering coordinate system to that of the PDF. This metadata was encoded in the PDF file as a PDF dictionary called LGIDict. My notes indicate that Alan came up with the LGIDict version 1 schema. I Ling Xu initially documented the schema and I gave its name: LGIDict -- LGI Geospatial Information Dictionary. At the time, I didn't know about Acrobat developer's prefixes, and JB didn't bust me on it.

Even as LGIDict version 1 was being drafted in 2002 -- we had deadlines and product to ship! -- the limitations were obvious. In 2003 I started working on a second version with provisions to drive a coordinate transformation engine. The LGIDict version 2 was cut in November of 2003.

Friday, May 01, 2009

OGC Publishes GeoPDF 2.2 as OGC Best Practice

After much anticipation, GeoPDF 2.2 has been published as an OGC Best Practice. From the page:

The intended audience of this document is a developer of software for creating GeoPDF. It specifies how to create the necessary PDF objects that identify a region of the PDF page as a map and describe the map’s coordinate systems. Map creation and rendering to a PDF page are not addressed. The underlying PDF file format is not addressed. The file format is specified in PDF Reference .
The reader will need knowledge of PDF objects and document structure. An understanding of cartographic projections and datums will also be helpful. Information about these can be found in Map Projections A Working Manual .
Though written with the PDF 1.7 file format in mind, this Best Practice is believed to be valid for all versions of the PDF file specification prior to PDF 1.7.