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# The GDAL C library, OGR exception, and the Field object
from django.contrib.gis.gdal.base import GDALBase
from django.contrib.gis.gdal.error import OGRException, OGRIndexError
from django.contrib.gis.gdal.field import Field
from django.contrib.gis.gdal.geometries import OGRGeometry, OGRGeomType
from django.contrib.gis.gdal.srs import SpatialReference
# ctypes function prototypes
from django.contrib.gis.gdal.prototypes import ds as capi, geom as geom_api
# For more information, see the OGR C API source code:
# http://www.gdal.org/ogr/ogr__api_8h.html
#
# The OGR_F_* routines are relevant here.
class Feature(GDALBase):
"A class that wraps an OGR Feature, needs to be instantiated from a Layer object."
#### Python 'magic' routines ####
def __init__(self, feat, fdefn):
"Initializes on the pointers for the feature and the layer definition."
if not feat or not fdefn:
raise OGRException('Cannot create OGR Feature, invalid pointer given.')
self.ptr = feat
self._fdefn = fdefn
def __del__(self):
"Releases a reference to this object."
if self._ptr: capi.destroy_feature(self._ptr)
def __getitem__(self, index):
"""
Gets the Field object at the specified index, which may be either
an integer or the Field's string label. Note that the Field object
is not the field's _value_ -- use the `get` method instead to
retrieve the value (e.g. an integer) instead of a Field instance.
"""
if isinstance(index, basestring):
i = self.index(index)
else:
if index < 0 or index > self.num_fields:
raise OGRIndexError('index out of range')
i = index
return Field(self.ptr, i)
def __iter__(self):
"Iterates over each field in the Feature."
for i in xrange(self.num_fields):
yield self[i]
def __len__(self):
"Returns the count of fields in this feature."
return self.num_fields
def __str__(self):
"The string name of the feature."
return 'Feature FID %d in Layer<%s>' % (self.fid, self.layer_name)
def __eq__(self, other):
"Does equivalence testing on the features."
return bool(capi.feature_equal(self.ptr, other._ptr))
#### Feature Properties ####
@property
def fid(self):
"Returns the feature identifier."
return capi.get_fid(self.ptr)
@property
def layer_name(self):
"Returns the name of the layer for the feature."
return capi.get_feat_name(self._fdefn)
@property
def num_fields(self):
"Returns the number of fields in the Feature."
return capi.get_feat_field_count(self.ptr)
@property
def fields(self):
"Returns a list of fields in the Feature."
return [capi.get_field_name(capi.get_field_defn(self._fdefn, i))
for i in xrange(self.num_fields)]
@property
def geom(self):
"Returns the OGR Geometry for this Feature."
# Retrieving the geometry pointer for the feature.
geom_ptr = capi.get_feat_geom_ref(self.ptr)
return OGRGeometry(geom_api.clone_geom(geom_ptr))
@property
def geom_type(self):
"Returns the OGR Geometry Type for this Feture."
return OGRGeomType(capi.get_fd_geom_type(self._fdefn))
#### Feature Methods ####
def get(self, field):
"""
Returns the value of the field, instead of an instance of the Field
object. May take a string of the field name or a Field object as
parameters.
"""
field_name = getattr(field, 'name', field)
return self[field_name].value
def index(self, field_name):
"Returns the index of the given field name."
i = capi.get_field_index(self.ptr, field_name)
if i < 0: raise OGRIndexError('invalid OFT field name given: "%s"' % field_name)
return i
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