337 lines
11 KiB
Python
337 lines
11 KiB
Python
"""
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The Spatial Reference class, represensents OGR Spatial Reference objects.
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Example:
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>>> from django.contrib.gis.gdal import SpatialReference
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>>> srs = SpatialReference('WGS84')
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>>> print srs
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GEOGCS["WGS 84",
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DATUM["WGS_1984",
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SPHEROID["WGS 84",6378137,298.257223563,
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AUTHORITY["EPSG","7030"]],
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TOWGS84[0,0,0,0,0,0,0],
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AUTHORITY["EPSG","6326"]],
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PRIMEM["Greenwich",0,
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AUTHORITY["EPSG","8901"]],
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UNIT["degree",0.01745329251994328,
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AUTHORITY["EPSG","9122"]],
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AUTHORITY["EPSG","4326"]]
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>>> print srs.proj
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+proj=longlat +ellps=WGS84 +datum=WGS84 +no_defs
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>>> print srs.ellipsoid
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(6378137.0, 6356752.3142451793, 298.25722356300003)
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>>> print srs.projected, srs.geographic
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False True
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>>> srs.import_epsg(32140)
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>>> print srs.name
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NAD83 / Texas South Central
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"""
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from ctypes import byref, c_char_p, c_int
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# Getting the error checking routine and exceptions
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from django.contrib.gis.gdal.base import GDALBase
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from django.contrib.gis.gdal.error import SRSException
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from django.contrib.gis.gdal.prototypes import srs as capi
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#### Spatial Reference class. ####
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class SpatialReference(GDALBase):
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"""
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A wrapper for the OGRSpatialReference object. According to the GDAL Web site,
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the SpatialReference object "provide[s] services to represent coordinate
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systems (projections and datums) and to transform between them."
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"""
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#### Python 'magic' routines ####
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def __init__(self, srs_input=''):
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"""
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Creates a GDAL OSR Spatial Reference object from the given input.
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The input may be string of OGC Well Known Text (WKT), an integer
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EPSG code, a PROJ.4 string, and/or a projection "well known" shorthand
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string (one of 'WGS84', 'WGS72', 'NAD27', 'NAD83').
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"""
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buf = c_char_p('')
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srs_type = 'user'
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if isinstance(srs_input, basestring):
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# Encoding to ASCII if unicode passed in.
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if isinstance(srs_input, unicode):
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srs_input = srs_input.encode('ascii')
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try:
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# If SRID is a string, e.g., '4326', then make acceptable
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# as user input.
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srid = int(srs_input)
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srs_input = 'EPSG:%d' % srid
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except ValueError:
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pass
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elif isinstance(srs_input, (int, long)):
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# EPSG integer code was input.
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srs_type = 'epsg'
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elif isinstance(srs_input, self.ptr_type):
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srs = srs_input
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srs_type = 'ogr'
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else:
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raise TypeError('Invalid SRS type "%s"' % srs_type)
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if srs_type == 'ogr':
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# Input is already an SRS pointer.
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srs = srs_input
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else:
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# Creating a new SRS pointer, using the string buffer.
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srs = capi.new_srs(buf)
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# If the pointer is NULL, throw an exception.
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if not srs:
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raise SRSException('Could not create spatial reference from: %s' % srs_input)
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else:
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self.ptr = srs
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# Importing from either the user input string or an integer SRID.
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if srs_type == 'user':
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self.import_user_input(srs_input)
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elif srs_type == 'epsg':
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self.import_epsg(srs_input)
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def __del__(self):
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"Destroys this spatial reference."
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if self._ptr: capi.release_srs(self._ptr)
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def __getitem__(self, target):
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"""
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Returns the value of the given string attribute node, None if the node
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doesn't exist. Can also take a tuple as a parameter, (target, child),
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where child is the index of the attribute in the WKT. For example:
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>>> wkt = 'GEOGCS["WGS 84", DATUM["WGS_1984, ... AUTHORITY["EPSG","4326"]]')
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>>> srs = SpatialReference(wkt) # could also use 'WGS84', or 4326
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>>> print srs['GEOGCS']
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WGS 84
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>>> print srs['DATUM']
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WGS_1984
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>>> print srs['AUTHORITY']
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EPSG
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>>> print srs['AUTHORITY', 1] # The authority value
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4326
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>>> print srs['TOWGS84', 4] # the fourth value in this wkt
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0
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>>> print srs['UNIT|AUTHORITY'] # For the units authority, have to use the pipe symbole.
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EPSG
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>>> print srs['UNIT|AUTHORITY', 1] # The authority value for the untis
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9122
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"""
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if isinstance(target, tuple):
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return self.attr_value(*target)
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else:
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return self.attr_value(target)
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def __str__(self):
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"The string representation uses 'pretty' WKT."
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return self.pretty_wkt
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#### SpatialReference Methods ####
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def attr_value(self, target, index=0):
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"""
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The attribute value for the given target node (e.g. 'PROJCS'). The index
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keyword specifies an index of the child node to return.
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"""
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if not isinstance(target, basestring) or not isinstance(index, int):
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raise TypeError
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return capi.get_attr_value(self.ptr, target, index)
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def auth_name(self, target):
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"Returns the authority name for the given string target node."
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return capi.get_auth_name(self.ptr, target)
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def auth_code(self, target):
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"Returns the authority code for the given string target node."
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return capi.get_auth_code(self.ptr, target)
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def clone(self):
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"Returns a clone of this SpatialReference object."
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return SpatialReference(capi.clone_srs(self.ptr))
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def from_esri(self):
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"Morphs this SpatialReference from ESRI's format to EPSG."
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capi.morph_from_esri(self.ptr)
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def identify_epsg(self):
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"""
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This method inspects the WKT of this SpatialReference, and will
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add EPSG authority nodes where an EPSG identifier is applicable.
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"""
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capi.identify_epsg(self.ptr)
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def to_esri(self):
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"Morphs this SpatialReference to ESRI's format."
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capi.morph_to_esri(self.ptr)
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def validate(self):
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"Checks to see if the given spatial reference is valid."
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capi.srs_validate(self.ptr)
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#### Name & SRID properties ####
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@property
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def name(self):
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"Returns the name of this Spatial Reference."
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if self.projected: return self.attr_value('PROJCS')
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elif self.geographic: return self.attr_value('GEOGCS')
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elif self.local: return self.attr_value('LOCAL_CS')
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else: return None
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@property
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def srid(self):
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"Returns the SRID of top-level authority, or None if undefined."
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try:
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return int(self.attr_value('AUTHORITY', 1))
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except (TypeError, ValueError):
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return None
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#### Unit Properties ####
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@property
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def linear_name(self):
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"Returns the name of the linear units."
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units, name = capi.linear_units(self.ptr, byref(c_char_p()))
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return name
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@property
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def linear_units(self):
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"Returns the value of the linear units."
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units, name = capi.linear_units(self.ptr, byref(c_char_p()))
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return units
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@property
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def angular_name(self):
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"Returns the name of the angular units."
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units, name = capi.angular_units(self.ptr, byref(c_char_p()))
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return name
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@property
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def angular_units(self):
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"Returns the value of the angular units."
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units, name = capi.angular_units(self.ptr, byref(c_char_p()))
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return units
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@property
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def units(self):
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"""
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Returns a 2-tuple of the units value and the units name,
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and will automatically determines whether to return the linear
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or angular units.
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"""
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if self.projected or self.local:
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return capi.linear_units(self.ptr, byref(c_char_p()))
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elif self.geographic:
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return capi.angular_units(self.ptr, byref(c_char_p()))
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else:
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return (None, None)
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#### Spheroid/Ellipsoid Properties ####
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@property
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def ellipsoid(self):
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"""
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Returns a tuple of the ellipsoid parameters:
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(semimajor axis, semiminor axis, and inverse flattening)
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"""
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return (self.semi_major, self.semi_minor, self.inverse_flattening)
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@property
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def semi_major(self):
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"Returns the Semi Major Axis for this Spatial Reference."
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return capi.semi_major(self.ptr, byref(c_int()))
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@property
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def semi_minor(self):
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"Returns the Semi Minor Axis for this Spatial Reference."
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return capi.semi_minor(self.ptr, byref(c_int()))
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@property
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def inverse_flattening(self):
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"Returns the Inverse Flattening for this Spatial Reference."
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return capi.invflattening(self.ptr, byref(c_int()))
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#### Boolean Properties ####
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@property
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def geographic(self):
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"""
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Returns True if this SpatialReference is geographic
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(root node is GEOGCS).
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"""
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return bool(capi.isgeographic(self.ptr))
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@property
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def local(self):
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"Returns True if this SpatialReference is local (root node is LOCAL_CS)."
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return bool(capi.islocal(self.ptr))
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@property
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def projected(self):
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"""
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Returns True if this SpatialReference is a projected coordinate system
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(root node is PROJCS).
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"""
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return bool(capi.isprojected(self.ptr))
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#### Import Routines #####
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def import_epsg(self, epsg):
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"Imports the Spatial Reference from the EPSG code (an integer)."
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capi.from_epsg(self.ptr, epsg)
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def import_proj(self, proj):
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"Imports the Spatial Reference from a PROJ.4 string."
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capi.from_proj(self.ptr, proj)
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def import_user_input(self, user_input):
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"Imports the Spatial Reference from the given user input string."
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capi.from_user_input(self.ptr, user_input)
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def import_wkt(self, wkt):
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"Imports the Spatial Reference from OGC WKT (string)"
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capi.from_wkt(self.ptr, byref(c_char_p(wkt)))
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def import_xml(self, xml):
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"Imports the Spatial Reference from an XML string."
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capi.from_xml(self.ptr, xml)
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#### Export Properties ####
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@property
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def wkt(self):
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"Returns the WKT representation of this Spatial Reference."
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return capi.to_wkt(self.ptr, byref(c_char_p()))
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@property
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def pretty_wkt(self, simplify=0):
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"Returns the 'pretty' representation of the WKT."
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return capi.to_pretty_wkt(self.ptr, byref(c_char_p()), simplify)
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@property
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def proj(self):
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"Returns the PROJ.4 representation for this Spatial Reference."
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return capi.to_proj(self.ptr, byref(c_char_p()))
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@property
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def proj4(self):
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"Alias for proj()."
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return self.proj
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@property
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def xml(self, dialect=''):
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"Returns the XML representation of this Spatial Reference."
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return capi.to_xml(self.ptr, byref(c_char_p()), dialect)
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class CoordTransform(GDALBase):
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"The coordinate system transformation object."
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def __init__(self, source, target):
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"Initializes on a source and target SpatialReference objects."
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if not isinstance(source, SpatialReference) or not isinstance(target, SpatialReference):
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raise TypeError('source and target must be of type SpatialReference')
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self.ptr = capi.new_ct(source._ptr, target._ptr)
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self._srs1_name = source.name
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self._srs2_name = target.name
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def __del__(self):
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"Deletes this Coordinate Transformation object."
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if self._ptr: capi.destroy_ct(self._ptr)
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def __str__(self):
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return 'Transform from "%s" to "%s"' % (self._srs1_name, self._srs2_name)
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