136 lines
5.0 KiB
Python
136 lines
5.0 KiB
Python
"""
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DataSource is a wrapper for the OGR Data Source object, which provides
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an interface for reading vector geometry data from many different file
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formats (including ESRI shapefiles).
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When instantiating a DataSource object, use the filename of a
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GDAL-supported data source. For example, a SHP file or a
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TIGER/Line file from the government.
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The ds_driver keyword is used internally when a ctypes pointer
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is passed in directly.
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Example:
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ds = DataSource('/home/foo/bar.shp')
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for layer in ds:
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for feature in layer:
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# Getting the geometry for the feature.
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g = feature.geom
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# Getting the 'description' field for the feature.
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desc = feature['description']
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# We can also increment through all of the fields
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# attached to this feature.
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for field in feature:
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# Get the name of the field (e.g. 'description')
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nm = field.name
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# Get the type (integer) of the field, e.g. 0 => OFTInteger
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t = field.type
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# Returns the value the field; OFTIntegers return ints,
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# OFTReal returns floats, all else returns string.
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val = field.value
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"""
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# ctypes prerequisites.
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from ctypes import byref
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# The GDAL C library, OGR exceptions, and the Layer object.
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from django.contrib.gis.gdal.base import GDALBase
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from django.contrib.gis.gdal.driver import Driver
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from django.contrib.gis.gdal.error import OGRException, OGRIndexError
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from django.contrib.gis.gdal.layer import Layer
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# Getting the ctypes prototypes for the DataSource.
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from django.contrib.gis.gdal.prototypes import ds as capi
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from django.utils.encoding import force_bytes, force_text
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from django.utils import six
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from django.utils.six.moves import xrange
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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_DS_* routines are relevant here.
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class DataSource(GDALBase):
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"Wraps an OGR Data Source object."
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#### Python 'magic' routines ####
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def __init__(self, ds_input, ds_driver=False, write=False, encoding='utf-8'):
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# The write flag.
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if write:
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self._write = 1
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else:
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self._write = 0
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# See also http://trac.osgeo.org/gdal/wiki/rfc23_ogr_unicode
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self.encoding = encoding
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# Registering all the drivers, this needs to be done
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# _before_ we try to open up a data source.
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if not capi.get_driver_count():
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capi.register_all()
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if isinstance(ds_input, six.string_types):
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# The data source driver is a void pointer.
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ds_driver = Driver.ptr_type()
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try:
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# OGROpen will auto-detect the data source type.
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ds = capi.open_ds(force_bytes(ds_input), self._write, byref(ds_driver))
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except OGRException:
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# Making the error message more clear rather than something
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# like "Invalid pointer returned from OGROpen".
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raise OGRException('Could not open the datasource at "%s"' % ds_input)
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elif isinstance(ds_input, self.ptr_type) and isinstance(ds_driver, Driver.ptr_type):
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ds = ds_input
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else:
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raise OGRException('Invalid data source input type: %s' % type(ds_input))
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if bool(ds):
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self.ptr = ds
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self.driver = Driver(ds_driver)
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else:
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# Raise an exception if the returned pointer is NULL
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raise OGRException('Invalid data source file "%s"' % ds_input)
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def __del__(self):
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"Destroys this DataStructure object."
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if self._ptr: capi.destroy_ds(self._ptr)
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def __iter__(self):
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"Allows for iteration over the layers in a data source."
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for i in xrange(self.layer_count):
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yield self[i]
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def __getitem__(self, index):
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"Allows use of the index [] operator to get a layer at the index."
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if isinstance(index, six.string_types):
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l = capi.get_layer_by_name(self.ptr, force_bytes(index))
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if not l: raise OGRIndexError('invalid OGR Layer name given: "%s"' % index)
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elif isinstance(index, int):
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if index < 0 or index >= self.layer_count:
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raise OGRIndexError('index out of range')
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l = capi.get_layer(self._ptr, index)
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else:
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raise TypeError('Invalid index type: %s' % type(index))
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return Layer(l, self)
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def __len__(self):
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"Returns the number of layers within the data source."
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return self.layer_count
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def __str__(self):
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"Returns OGR GetName and Driver for the Data Source."
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return '%s (%s)' % (self.name, str(self.driver))
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@property
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def layer_count(self):
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"Returns the number of layers in the data source."
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return capi.get_layer_count(self._ptr)
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@property
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def name(self):
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"Returns the name of the data source."
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name = capi.get_ds_name(self._ptr)
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return force_text(name, self.encoding, strings_only=True)
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