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PDF20 Spec 12 Geospatial
Part of: PDF20-Spec-12-Interactive
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12.10
Geospatial features
12.10.1
General
PDF is a common delivery mechanism for map and satellite imagery data. In PDF 2.0, a geospatial coordinate system is introduced ("Table 266 — Entries in a measure dictionary") along with a number of PDF constructs, as explained in this clause, to support geospatially registered content.
12.10.2
Geospatial measure dictionary
When the subtype of a measurement dictionary ("Table 266 — Entries in a measure dictionary") is GEO, additional entries are defined through a geospatial measure dictionary. A geospatial measure dictionary, "Table 269 — Additional entries in a geospatial measure dictionary", contains a description of the earth-based coordinate system associated with the PDF object, and corresponding arrays of points in that coordinate system and the local object coordinate system. It may © ISO 2020 – All rights reserved
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contain a bounding polygon (the Bounds entry), which defines the region of the PDF object for which the geographic associations are valid. It may also contain a choice of default units (the PDU entry) for user displays of positions, distances and areas. An optional display coordinate system (the DCS entry) allows a document to be authored to display values in a coordinate system other than that associated with the source data. For example, a map may be created in a state planar coordinate system based on a 1927 datum, but it is possible to display its latitude and longitude values in the WGS84 datum corresponding to values reported by a GPS device. The entries of a geospatial measure dictionary are shown in "Table 269 — Additional entries in a geospatial measure dictionary". Table 269 — Additional entries in a geospatial measure dictionary Key
Type
Description
Bounds
array
(Optional; PDF 2.0) An array of numbers that shall be taken pairwise to define a series of points that describes the bounds of an area for which geospatial transformations are valid. For maps, this bounding polygon is known as a neatline. These numbers are expressed relative to a unit square that describes the BBox associated with a Viewport or form XObject, or the bounds of an image XObject. If not present, the default values shall define a rectangle describing the full unit square, with values of [0.0 0.0 0.0 1.0 1.0 1.0 1.0 0.0]. NOTE 1 The polygon description need not be explicitly closed by repeating the first point values as a final point.
GCS
dictionary
(Required; PDF 2.0) A geographic or projected coordinate system dictionary. See "Table 270 — Entries in a geographic coordinate system dictionary" and "Table 271 — Entries in a projected coordinate system dictionary".
DCS
dictionary
(Optional; PDF 2.0) A projected or geographic coordinate system that shall be used for the display of position values, such as latitude and longitude. See "Table 270 — Entries in a geographic coordinate system dictionary" and "Table 271 — Entries in a projected coordinate system dictionary". Formatting the displayed representation of these values is controlled by the interactive PDF processor.
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Key
Type
Description
PDU
array
(Optional; PDF 2.0) Preferred Display Units. An array of three names that identify in order a linear display unit, an area display unit, and an angular display unit. The following are valid linear display units: M a metre KM a kilometre FT an international foot USFT a U.S. Survey foot MI an international mile NM an international nautical mile The following are valid area display units: SQM a square metre HA a hectare (10,000 square metres) SQKM a square kilometre SQFT a square foot (US Survey) A an acre SQMI a square mile (international) The following are valid angular display units: DEG a degree GRD a grad (1/400 of a circle, or 0.9 degrees)
GPTS
array
(Required; PDF 2.0) An array of numbers that shall be taken pairwise, defining points in geographic space as degrees of latitude and longitude, respectively when defining a geographic coordinate system. These values shall be based on the geographic coordinate system described in the GCS dictionary. When defining a projected coordinate system, this array contains values in a planar projected coordinate space as eastings and northings. For Geospatial3D, when Geospatial feature information is present (requirement type Geospatial3D) in a 3D annotation, the GPTS array is required to hold 3D point coordinates as triples rather than pairwise where the third value of each tripe is an elevation value. NOTE 2 Any projected coordinate system includes an underlying geographic coordinate system.
LPTS
array
(Optional; PDF 2.0) An array of numbers that shall be taken pairwise to define points in a 2D unit square. The unit square is mapped to the rectangular bounds of the Viewport, image XObject, or forms XObject that contains the measure dictionary. This array shall contain the same number of number pairs as the GPTS array; each number pair is the unit square object position corresponding to the geospatial position in the GPTS array. For Geospatial3D, when Geospatial feature information is present in a 3D annotation (requirement type Geospatial3D), the LPTS array is required to hold 3D point coordinates as triples corresponding to the GPTS array in the 3D annotation view world coordinate space.
PCSM
array
(Optional; PDF 2.0) A 12-element transformation matrix of real numbers, defining the transformation from XObject position coordinates to projected coordinate system. If GCS is a geographic coordinate system dictionary then PCSM should be ignored and GTPS used instead. If PCSM is present, it has priority over GPTS, and GPTS values may be ignored. This priority provides backward compatibility. NOTE 3 PCSM is an acronym for "Projected Coordinate System Matrix".
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12.10.3
Geographic coordinate system dictionary
A geographic coordinate system (GEOGCS) specifies an ellipsoidal object in geographic coordinates: angular units of latitude and longitude. The geographic coordinate system shall be described in either or both of two well-established standards: as a numeric EPSG reference code, or as a Well Known Text (WKT) string, which contains a description of algorithms and parameters needed for transformations. "Table 270 — Entries in a geographic coordinate system dictionary" lists the entries in a geographic coordinate system dictionary. A geographic coordinate system dictionary may be a value of the GCS or the DCS entry of a geospatial measure dictionary. (See "Table 269 — Additional entries in a geospatial measure dictionary".) Table 270 — Entries in a geographic coordinate system dictionary Key
Type
Description
Type
name
(Required; PDF 2.0) The type of PDF object that this dictionary describes. If present, shall be GEOGCS for a geographic coordinate system dictionary.
EPSG
integer
(Optional; PDF 2.0) An EPSG reference code specifying the geographic coordinate system. Shall not be present if WKT is present.
WKT
ASCII string
(Optional; PDF 2.0) A string of Well Known Text describing the geographic coordinate system. Shall not be present if EPSG is present.
Either an EPSG code or a WKT string shall be present in a geographic coordinate system dictionary. The EPSG reference codes are described in a database available through http://www.epsg.org as administered by the International Association of Oil and Gas Producers (OGP). The WKT (Well Known Text) format is specified in ISO 19162.
12.10.4
Projected coordinate system dictionary
A projected coordinate system (PROJCS), which includes an embedded GEOGCS, specifies the algorithms and associated parameters used to transform points between geographic coordinates and a two-dimensional (projected) coordinate system. Any transformation between a three-dimensional curved geographic coordinate system and a two-dimensional coordinate system introduces distortions. For small areas, this distortion may be small enough to allow direct mapping between geographic coordinates and PDF object coordinates without requiring the use of a projected coordinate system. The projected coordinate system shall be described in either or both of two well-established standards: as a numeric EPSG reference code, or as a Well KnownText (WKT) string, which contains a description of algorithms and parameters needed for transformations. "Table 271 — Entries in a projected coordinate system dictionary" lists the entries in a projected coordinate system dictionary. A projected coordinate system dictionary may be a value of the GCS or the DCS entry of a geospatial measure dictionary, "Table 269 — Additional entries in a geospatial measure dictionary". 604
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Table 271 — Entries in a projected coordinate system dictionary Key
Type
Description
Type
name
EPSG
integer
(Required; PDF 2.0) The type of PDF object that this dictionary describes; shall be PROJCS for a projected coordinate system dictionary. (Optional; PDF 2.0) An EPSG reference code specifying the projected coordinate system.
WKT
ASCII string
(Optional; PDF 2.0) A string of Well Known Text describing the projected coordinate system.
Either an EPSG code or a WKT string shall be required in the projected coordinate system dictionary. EXAMPLE 1
A WKT describing a geographic coordinate system An example of WKT description of a geographic coordinate system, formatted for readability. The EPSG code equivalent to the GCS_North_American_1983 geographic coordinate system is 4269.
GEOGCS["GCS_North_American_1983", DATUM[ "D_North_American_1983", SPHEROID["GRS_1980",6378137.0,298.257222101] ], PRIMEM["Greenwich",0.0], UNIT["Degree",0.0174532925199433] ]
EXAMPLE 2
A WKT describing a projected coordinate system An example of WKT description of a projected coordinate system, formatted for readability. The EPSG code equivalent to the North_American_Albers_Equal_Area_Conic projected coordinate system is 102008.
PROJCS["North_America_Albers_Equal_Area_Conic", GEOGCS["GCS_North_American_1983", DATUM["D_North_American_1983", SPHEROID["GRS_1980",6378137.0, 298.257222101] ], PRIMEM["Greenwich",0.0], UNIT["Degree",0.0174532925199433] ], PROJECTION["Albers"], PARAMETER["False_Easting",0.0], PARAMETER["False_Northing",0.0], PARAMETER["Central_Meridian",-96.0], PARAMETER["Standard_Parallel_1",20.0], PARAMETER["Standard_Parallel_2",60.0] PARAMETER["Latitude_Of_Origin",40.0], UNIT["Meter",1.0] ]
12.10.5
Point data dictionary
Any 2D object (Viewport, image XObject, or form XObject) that contains a measure dictionary ("Table 266 — Entries in a measure dictionary") of subtype GEO can optionally include a PtData entry. The value of a PtData entry is a point data dictionary or an array of point data dictionaries of extended data associated with points in the 2D space. "Table 272 — Entries in a point data dictionary" lists the entries of a point data dictionary. © ISO 2020 – All rights reserved
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Table 272 — Entries in a point data dictionary Key
Type
Description
Type
name
(Required; PDF 2.0) The type of PDF object that this dictionary describes; shall be PtData for a point data dictionary.
Subtype
name
(Required; PDF 2.0) Shall be Cloud.
Names
array
(Required; PDF 2.0) An array of names that identify the internal data elements of the individual point arrays in the XPTS array. There are three predefined names: LAT latitude in degrees. The XPTS value is a number type. LON longitude in degrees. The XPTS value is a number type. ALT altitude in metres. The XPTS value is a number type. NOTE
XPTS
array
These names are, in effect, column headers for the array of XPTS values.
(Required; PDF 2.0) An array of arrays of values. The number of members in each interior array shall correspond to the size of the Names array; each member in the interior arrays is of a type defined by the corresponding name in the Names array. The XPTS array is a collection of tuples without any guaranteed ordering or relationship from point to point.
The names LAT, LON, and ALT are predefined, and shall be used to associate altitude information with latitude and longitude positions.
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