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"""
DataSource is a wrapper for the OGR Data Source object, which provides
an interface for reading vector geometry data from many different file
formats (including ESRI shapefiles).
When instantiating a DataSource object, use the filename of a
GDAL-supported data source. For example, a SHP file or a
TIGER/Line file from the government.
The ds_driver keyword is used internally when a ctypes pointer
is passed in directly.
Example:
ds = DataSource('/home/foo/bar.shp')
for layer in ds:
for feature in layer:
# Getting the geometry for the feature.
g = feature.geom
# Getting the 'description' field for the feature.
desc = feature['description']
# We can also increment through all of the fields
# attached to this feature.
for field in feature:
# Get the name of the field (e.g. 'description')
nm = field.name
# Get the type (integer) of the field, e.g. 0 => OFTInteger
t = field.type
# Returns the value the field; OFTIntegers return ints,
# OFTReal returns floats, all else returns string.
val = field.value
"""
# ctypes prerequisites.
from ctypes import byref, c_void_p
# The GDAL C library, OGR exceptions, and the Layer object.
from django.contrib.gis.gdal.driver import Driver
from django.contrib.gis.gdal.error import OGRException, OGRIndexError
from django.contrib.gis.gdal.layer import Layer
# Getting the ctypes prototypes for the DataSource.
from django.contrib.gis.gdal.prototypes.ds import \
destroy_ds, get_driver_count, register_all, open_ds, release_ds, \
get_ds_name, get_layer, get_layer_count, get_layer_by_name
# For more information, see the OGR C API source code:
# http://www.gdal.org/ogr/ogr__api_8h.html
#
# The OGR_DS_* routines are relevant here.
class DataSource(object):
"Wraps an OGR Data Source object."
#### Python 'magic' routines ####
def __init__(self, ds_input, ds_driver=False, write=False):
# DataSource pointer is initially NULL.
self._ptr = None
# The write flag.
if write:
self._write = 1
else:
self._write = 0
# Registering all the drivers, this needs to be done
# _before_ we try to open up a data source.
if not get_driver_count(): register_all()
if isinstance(ds_input, basestring):
# The data source driver is a void pointer.
ds_driver = c_void_p()
try:
# OGROpen will auto-detect the data source type.
ds = open_ds(ds_input, self._write, byref(ds_driver))
except OGRException:
# Making the error message more clear rather than something
# like "Invalid pointer returned from OGROpen".
raise OGRException('Could not open the datasource at "%s"' % ds_input)
elif isinstance(ds_input, c_void_p) and isinstance(ds_driver, c_void_p):
ds = ds_input
else:
raise OGRException('Invalid data source input type: %s' % type(ds_input))
if bool(ds):
self._ptr = ds
self._driver = Driver(ds_driver)
else:
# Raise an exception if the returned pointer is NULL
raise OGRException('Invalid data source file "%s"' % ds_input)
def __del__(self):
"Destroys this DataStructure object."
if self._ptr: destroy_ds(self._ptr)
def __iter__(self):
"Allows for iteration over the layers in a data source."
for i in xrange(self.layer_count):
yield self[i]
def __getitem__(self, index):
"Allows use of the index [] operator to get a layer at the index."
if isinstance(index, basestring):
l = get_layer_by_name(self._ptr, index)
if not l: raise OGRIndexError('invalid OGR Layer name given: "%s"' % index)
elif isinstance(index, int):
if index < 0 or index >= self.layer_count:
raise OGRIndexError('index out of range')
l = get_layer(self._ptr, index)
else:
raise TypeError('Invalid index type: %s' % type(index))
return Layer(l)
def __len__(self):
"Returns the number of layers within the data source."
return self.layer_count
def __str__(self):
"Returns OGR GetName and Driver for the Data Source."
return '%s (%s)' % (self.name, str(self.driver))
#### DataSource Properties ####
@property
def driver(self):
"Returns the Driver object for this Data Source."
return self._driver
@property
def layer_count(self):
"Returns the number of layers in the data source."
return get_layer_count(self._ptr)
@property
def name(self):
"Returns the name of the data source."
return get_ds_name(self._ptr)
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