+
−# 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))