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# Needed ctypes routines
from ctypes import byref
# Other GDAL imports.
from django.contrib.gis.gdal.envelope import Envelope, OGREnvelope
from django.contrib.gis.gdal.error import OGRException, OGRIndexError, SRSException
from django.contrib.gis.gdal.feature import Feature
from django.contrib.gis.gdal.field import FIELD_CLASSES
from django.contrib.gis.gdal.geometries import OGRGeomType
from django.contrib.gis.gdal.srs import SpatialReference
# GDAL ctypes function prototypes.
from django.contrib.gis.gdal.prototypes.ds import \
get_extent, get_fd_geom_type, get_fd_name, get_feature, get_feature_count, \
get_field_count, get_field_defn, get_field_name, get_field_precision, \
get_field_width, get_field_type, get_layer_defn, get_layer_srs, \
get_next_feature, reset_reading, test_capability
from django.contrib.gis.gdal.prototypes.srs import clone_srs
# For more information, see the OGR C API source code:
# http://www.gdal.org/ogr/ogr__api_8h.html
#
# The OGR_L_* routines are relevant here.
class Layer(object):
"A class that wraps an OGR Layer, needs to be instantiated from a DataSource object."
#### Python 'magic' routines ####
def __init__(self, layer_ptr):
"Needs a C pointer (Python/ctypes integer) in order to initialize."
self._ptr = None # Initially NULL
if not layer_ptr:
raise OGRException('Cannot create Layer, invalid pointer given')
self._ptr = layer_ptr
self._ldefn = get_layer_defn(self._ptr)
# Does the Layer support random reading?
self._random_read = self.test_capability('RandomRead')
def __getitem__(self, index):
"Gets the Feature at the specified index."
if isinstance(index, (int, long)):
# An integer index was given -- we cannot do a check based on the
# number of features because the beginning and ending feature IDs
# are not guaranteed to be 0 and len(layer)-1, respectively.
if index < 0: raise OGRIndexError('Negative indices are not allowed on OGR Layers.')
return self._make_feature(index)
elif isinstance(index, slice):
# A slice was given
start, stop, stride = index.indices(self.num_feat)
return [self._make_feature(fid) for fid in xrange(start, stop, stride)]
else:
raise TypeError('Integers and slices may only be used when indexing OGR Layers.')
def __iter__(self):
"Iterates over each Feature in the Layer."
# ResetReading() must be called before iteration is to begin.
reset_reading(self._ptr)
for i in xrange(self.num_feat):
yield Feature(get_next_feature(self._ptr), self._ldefn)
def __len__(self):
"The length is the number of features."
return self.num_feat
def __str__(self):
"The string name of the layer."
return self.name
def _make_feature(self, feat_id):
"""
Helper routine for __getitem__ that constructs a Feature from the given
Feature ID. If the OGR Layer does not support random-access reading,
then each feature of the layer will be incremented through until the
a Feature is found matching the given feature ID.
"""
if self._random_read:
# If the Layer supports random reading, return.
try:
return Feature(get_feature(self._ptr, feat_id), self._ldefn)
except OGRException:
pass
else:
# Random access isn't supported, have to increment through
# each feature until the given feature ID is encountered.
for feat in self:
if feat.fid == feat_id: return feat
# Should have returned a Feature, raise an OGRIndexError.
raise OGRIndexError('Invalid feature id: %s.' % feat_id)
#### Layer properties ####
@property
def extent(self):
"Returns the extent (an Envelope) of this layer."
env = OGREnvelope()
get_extent(self._ptr, byref(env), 1)
return Envelope(env)
@property
def name(self):
"Returns the name of this layer in the Data Source."
return get_fd_name(self._ldefn)
@property
def num_feat(self, force=1):
"Returns the number of features in the Layer."
return get_feature_count(self._ptr, force)
@property
def num_fields(self):
"Returns the number of fields in the Layer."
return get_field_count(self._ldefn)
@property
def geom_type(self):
"Returns the geometry type (OGRGeomType) of the Layer."
return OGRGeomType(get_fd_geom_type(self._ldefn))
@property
def srs(self):
"Returns the Spatial Reference used in this Layer."
try:
ptr = get_layer_srs(self._ptr)
return SpatialReference(clone_srs(ptr))
except SRSException:
return None
@property
def fields(self):
"""
Returns a list of string names corresponding to each of the Fields
available in this Layer.
"""
return [get_field_name(get_field_defn(self._ldefn, i))
for i in xrange(self.num_fields) ]
@property
def field_types(self):
"""
Returns a list of the types of fields in this Layer. For example,
the list [OFTInteger, OFTReal, OFTString] would be returned for
an OGR layer that had an integer, a floating-point, and string
fields.
"""
return [FIELD_CLASSES[get_field_type(get_field_defn(self._ldefn, i))]
for i in xrange(self.num_fields)]
@property
def field_widths(self):
"Returns a list of the maximum field widths for the features."
return [get_field_width(get_field_defn(self._ldefn, i))
for i in xrange(self.num_fields)]
@property
def field_precisions(self):
"Returns the field precisions for the features."
return [get_field_precision(get_field_defn(self._ldefn, i))
for i in xrange(self.num_fields)]
#### Layer Methods ####
def get_fields(self, field_name):
"""
Returns a list containing the given field name for every Feature
in the Layer.
"""
if not field_name in self.fields:
raise OGRException('invalid field name: %s' % field_name)
return [feat.get(field_name) for feat in self]
def get_geoms(self, geos=False):
"""
Returns a list containing the OGRGeometry for every Feature in
the Layer.
"""
if geos:
from django.contrib.gis.geos import GEOSGeometry
return [GEOSGeometry(feat.geom.wkb) for feat in self]
else:
return [feat.geom for feat in self]
def test_capability(self, capability):
"""
Returns a bool indicating whether the this Layer supports the given
capability (a string). Valid capability strings include:
'RandomRead', 'SequentialWrite', 'RandomWrite', 'FastSpatialFilter',
'FastFeatureCount', 'FastGetExtent', 'CreateField', 'Transactions',
'DeleteFeature', and 'FastSetNextByIndex'.
"""
return bool(test_capability(self._ptr, capability))
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