Adobe Acrobat SDK
Interactive Features (Chapter 8 in PDF Reference)
Adobe® Supplement to the ISO 32000
8.8.1 Geospatial Features 51
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 can 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 8.111b 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 8.111a
on
page 50
.)
Either an
EPSG
code or a
WKT
string is required in a geographic coordinate system dictionary. (See
implementation note E-20,
page 132
.)
The EPSG reference codes are described in a database available through www.epsg.org, as administered
by the International Association of Oil and Gas Producers (OGP). Well Known Text is specified in document
01-009,
OpenGIS Implementation Specification: Coordinate Transformation Services
, of the Open Geospatial
Consortium. (See
Bibliography
.) See implementation note E-9,
page 131
.
GPTS
array
(
Required; ExtensionLevel 3
) An array of numbers taken pairwise,
defining points in geographic space as degrees of latitude and
longitude. These values are based on the geographic coordinate
system described in the GCS dictionary. (Note that any projected
coordinate system includes an underlying geographic coordinate
system.)
LPTS
array
(
Optional; ExtensionLevel 3
) An array of numbers taken pairwise that
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 contain the measure dictionary. This array contains
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.
TABLE 8.111a Additional entries specific in a geospatial measure dictionary
KEY
TYPE
VALUE
TABLE 8.111b Entries in a geographic coordinate system dictionary
KEY
TYPE
VALUE
Type
name
(
Required; ExtensionLevel 3
) The type of PDF object that this
dictionary describes; shall be
GEOGCS
for a geographic coordinate
system dictionary.
EPSG
integer
(
Optional; ExtensionLevel 3
) An EPSG reference code specifying the
geographic coordinate system.
WKT
ASCII string
(
Optional; ExtensionLevel 3
) A string of Well Known Text describing
the geographic coordinate system.
See implementation note E-8,
page 131
.
