Geoscience Reference
In-Depth Information
images, although it depends on how the GeoTIFF is defined (as pixel is area or point,
coordinates must then be shifted with half the pixel size.
GDAL supports various formats to define a SRS. Most convenient is the format of
a unique numeric code as introduced by European PetroleumSurveyGroup (EPSG).
4
The codes correspond to the EPSG geodetic parameter dataset, which is versioned.
The list of EPSG codes supported by GDAL/OGR with their corresponding coor-
dinate systems and parameters can be found in the files gcs.csv and pcs.csv. These
files are located in a directory defined by the environment variable
GDAL_DATA
that
is set during the installation of GDAL. To find out where they are on your system,
use the
gdal-config
command with the option
--datadir
. Here is a list of
projection formats supported by GDAL:
dstfile
The destination file name.
NAD27/NAD83/WGS84/WGS72
These common geographic (lat/long) coordinate systems can be used directly by
these names.
EPSG n
Coordinate systems (projected or geographic) can be selected based on their EPSG
codes, for instance EPSG:27700 is the British National Grid. A list of EPSG coor-
dinate systems can be found in the GDAL data files gcs.csv and pcs.csv.
PROJ.4 Definitions
A PROJ.4 definition string can be used as a coordinate system. For instance
“+proj=utm +zone=11 +datum=WGS84”. Take care to keep the PROJ.4 string
together as a single argument to the command (usually by double quoting).
OpenGIS Well Known Text
The Open GIS Consortium has defined a textual format for describing coordinate
systems as part of the Simple Features specifications. This format is the internal
working format for coordinate systems used in GDAL. The name of a file containing
a WKT coordinate system definition may be used a coordinate system argument, or
the entire coordinate system itself may be used as a command line option (though
escaping all the quotes in WKT is quite challenging).
ESRI Well Known Text
ESRI uses a slight variation on OGC WKT format in their ArcGIS product
(ArcGIS.prj files), and these may be used in a similar manner to WKT files, but the
filename should be prefixed with ESRI::. For example “ESRI::NAD 1927 StatePlane
Wyoming West FIPS 4904.prj”.
Spatial References from URLs
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