Georegistering PDF

D. Alan StewartTerraGo Technologies

Presentation to Atlanta ESRI Dev MeetupNovember 8, 2011

The Beginning

• Invented in 2002 by Layton Graphics, Inc.• The customer was SBC, now AT&T• Rendering engineering records to PDF• SBC wanted real-world measuring capability• Adobe Reader plugin transformed PDF

coordinates to UTM• If you can do one, why not do them all?• GeoPDF® and 2003 patent application

Evolution

• Free Adobe Reader plugin released• TerraGo Technologies spun out in 2005• Patent granted in 2008• TerraGo grants usage rights to Adobe• Adobe releases Reader 9• ESRI releases ArcGIS 9.3• New, competing georegistration method

Today

• New method submitted to ISO as part of the PDF specification (ISO method)

• Original method submitted to Open Geospatial Consortium (OGC method)

• TerraGo and Adobe support both methods• ISO supports more obscure coordinate

systems• OGC supports greater accuracy

How Does It Work?

• Applied to a PDF Page object• Specify an area on the page surface• Specify a map coordinate system• Specify a transformation

OGC MethodExcerpt from a Page dictionary:

/LGIDict << /Description (Title)/CTM [(35.28267) (0) (0) (35.28267) (205188.64) (3207094.8)]/Neatline [(72) (132) (153) (3274) (2888) (3215) (2834) (74)]/Projection <<

/Description (WGS 84 UTM 16N)/ProjectionType (TC)/Datum (WGE)/CentralMeridian (-87.0)/OriginLatitude (0.0)/FalseEasting (500000.0)/FalseNorthing (0.0)/ScaleFactor (0.999600)/Type /Projection

>> /Type /LGIDict/Version (2.1)

>>

ISO MethodExcerpt from a Page dictionary:

/VP [ <</Type /Viewport/Bbox [0 0 2960 3345]/Name (Title)/Measure <<

/Type /Measure/Subtype /GEO/Bounds [0 0 0 1 1 1 1 0]/GPTS [29.0 -90.0 30.0 -90.0 30.0 -89.0 29.0 -89.0]/LPTS [0.024324 0.039461 0.051689 0.978774 0.975675 0.961136 0.957432 0.022122]/GCS <<

/Type /PROJCS/WKT

(PROJCS["WGS_1984_UTM_Zone_16N",GEOGCS["GCS_WGS_1984",DATUM["D_WGS_1984",SPHEROID["WGS_1984",6378137,298.257223563]],PRIMEM["Greenwich",0],UNIT["Degree",0.017453292519943295]],PROJECTION["Transverse_Mercator"],PARAMETER["latitude_of_origin",0],PARAMETER["central_meridian",-87],PARAMETER["scale_factor",0.9996],PARAMETER["false_easting",500000],PARAMETER["false_northing",0],UNIT["Meter",1]])

>>>>

>>

Comparison

• OGC uses the /CTM key to specify the transformation from PDF to map

• ISO uses a combination of the /Bbox, /GPTS and /LPTS keys for the same

• OGC uses datum and projection codes, plus projection parameter keys to describe the map coordinate system

• ISO uses Well-Known Text for the same• OGC uses the /Neatline key to specify the map bounds• ISO uses the /Bounds key for the same

Additional Notes

• PDF transformations use the lower left corner of the page as the origin, unlike world files

• OGC uses PDF strings instead of PDF numbers for higher precision (PDF numbers are only32 bits)

• Well-Known Text used by ISO is general but poorly standardized

• ISO supports EPSG codes

One More Thing

TerraGo now supports 3D georegistration!

More Information

• TerraGo Technologieshttp://www.terragotech.comastewart@terragotech.com

• PDFhttp://home.comcast.net/~jk05/presentations/PDFTutorials.html

• OGC methodhttps://portal.opengeospatial.org/files/?artifact_id=40537

• ISO methodhttp://www.adobe.com/devnet/pdf/pdf_reference.html