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