Adobe Acrobat SDK
Interactive Features (Chapter 8 in PDF Reference)
Adobe® Supplement to the ISO 32000
8.8.1 Geospatial Features 52
Examples of WKT description strings appear at the end of the next section, beginning on
page 52
.
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 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.
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
.
Table 8.111c 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 8.111a on
page 50
.
Either an
EPSG
code or a
WKT
string is required in the projected coordinate system dictionary. (See
implementation note E-20,
page 132
.)
Example:
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]
]
TABLE 8.111c Entries in a projected coordinate system dictionary
KEY
TYPE
VALUE
Type
name
(
Required; ExtensionLevel 3
) The type of PDF object that this
dictionary describes; shall be
PROJCS
for a projected coordinate
system dictionary.
EPSG
integer
(
Optional; ExtensionLevel 3
) An EPSG reference code specifying the
projected coordinate system.
WKT
ASCII string
(
Optional; ExtensionLevel 3
) A string of Well Known Text describing
the projected coordinate system.
See implementation note E-8,
page 131
.
