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from ctypes import byref, c_double
from django.contrib.gis.gdal.base import GDALBase
from django.contrib.gis.gdal.envelope import Envelope, OGREnvelope
from django.contrib.gis.gdal.error import (
GDALException, OGRIndexError, SRSException,
)
from django.contrib.gis.gdal.feature import Feature
from django.contrib.gis.gdal.field import OGRFieldTypes
from django.contrib.gis.gdal.geometries import OGRGeometry
from django.contrib.gis.gdal.geomtype import OGRGeomType
from django.contrib.gis.gdal.prototypes import (
ds as capi, geom as geom_api, srs as srs_api,
)
from django.contrib.gis.gdal.srs import SpatialReference
from django.utils import six
from django.utils.encoding import force_bytes, force_text
from django.utils.six.moves import range
# 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(GDALBase):
"A class that wraps an OGR Layer, needs to be instantiated from a DataSource object."
def __init__(self, layer_ptr, ds):
"""
Initializes on an OGR C pointer to the Layer and the `DataSource` object
that owns this layer. The `DataSource` object is required so that a
reference to it is kept with this Layer. This prevents garbage
collection of the `DataSource` while this Layer is still active.
"""
if not layer_ptr:
raise GDALException('Cannot create Layer, invalid pointer given')
self.ptr = layer_ptr
self._ds = ds
self._ldefn = capi.get_layer_defn(self._ptr)
# Does the Layer support random reading?
self._random_read = self.test_capability(b'RandomRead')
def __getitem__(self, index):
"Gets the Feature at the specified index."
if isinstance(index, six.integer_types):
# 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 range(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.
capi.reset_reading(self._ptr)
for i in range(self.num_feat):
yield Feature(capi.get_next_feature(self._ptr), self)
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(capi.get_feature(self.ptr, feat_id), self)
except GDALException:
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()
capi.get_extent(self.ptr, byref(env), 1)
return Envelope(env)
@property
def name(self):
"Returns the name of this layer in the Data Source."
name = capi.get_fd_name(self._ldefn)
return force_text(name, self._ds.encoding, strings_only=True)
@property
def num_feat(self, force=1):
"Returns the number of features in the Layer."
return capi.get_feature_count(self.ptr, force)
@property
def num_fields(self):
"Returns the number of fields in the Layer."
return capi.get_field_count(self._ldefn)
@property
def geom_type(self):
"Returns the geometry type (OGRGeomType) of the Layer."
return OGRGeomType(capi.get_fd_geom_type(self._ldefn))
@property
def srs(self):
"Returns the Spatial Reference used in this Layer."
try:
ptr = capi.get_layer_srs(self.ptr)
return SpatialReference(srs_api.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 [force_text(capi.get_field_name(capi.get_field_defn(self._ldefn, i)),
self._ds.encoding, strings_only=True)
for i in range(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 [OGRFieldTypes[capi.get_field_type(capi.get_field_defn(self._ldefn, i))]
for i in range(self.num_fields)]
@property
def field_widths(self):
"Returns a list of the maximum field widths for the features."
return [capi.get_field_width(capi.get_field_defn(self._ldefn, i))
for i in range(self.num_fields)]
@property
def field_precisions(self):
"Returns the field precisions for the features."
return [capi.get_field_precision(capi.get_field_defn(self._ldefn, i))
for i in range(self.num_fields)]
def _get_spatial_filter(self):
try:
return OGRGeometry(geom_api.clone_geom(capi.get_spatial_filter(self.ptr)))
except GDALException:
return None
def _set_spatial_filter(self, filter):
if isinstance(filter, OGRGeometry):
capi.set_spatial_filter(self.ptr, filter.ptr)
elif isinstance(filter, (tuple, list)):
if not len(filter) == 4:
raise ValueError('Spatial filter list/tuple must have 4 elements.')
# Map c_double onto params -- if a bad type is passed in it
# will be caught here.
xmin, ymin, xmax, ymax = map(c_double, filter)
capi.set_spatial_filter_rect(self.ptr, xmin, ymin, xmax, ymax)
elif filter is None:
capi.set_spatial_filter(self.ptr, None)
else:
raise TypeError('Spatial filter must be either an OGRGeometry instance, a 4-tuple, or None.')
spatial_filter = property(_get_spatial_filter, _set_spatial_filter)
# #### Layer Methods ####
def get_fields(self, field_name):
"""
Returns a list containing the given field name for every Feature
in the Layer.
"""
if field_name not in self.fields:
raise GDALException('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(capi.test_capability(self.ptr, force_bytes(capability)))
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