webapp/django/contrib/gis/gdal/feature.py

# The GDAL C library, OGR exception, and the Field object
from django.contrib.gis.gdal.error import OGRException, OGRIndexError
from django.contrib.gis.gdal.field import Field
from django.contrib.gis.gdal.geometries import OGRGeometry, OGRGeomType
from django.contrib.gis.gdal.srs import SpatialReference

# ctypes function prototypes
from django.contrib.gis.gdal.prototypes.ds import \
    destroy_feature, feature_equal, get_fd_geom_type, get_feat_geom_ref, \
    get_feat_name, get_feat_field_count, get_fid, get_field_defn, \
    get_field_index, get_field_name
from django.contrib.gis.gdal.prototypes.geom import clone_geom, get_geom_srs
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_F_* routines are relevant here.
class Feature(object):
    "A class that wraps an OGR Feature, needs to be instantiated from a Layer object."

    #### Python 'magic' routines ####
    def __init__(self, feat, fdefn):
        "Initializes on the pointers for the feature and the layer definition."
        self._ptr = None # Initially NULL
        if not feat or not fdefn:
            raise OGRException('Cannot create OGR Feature, invalid pointer given.')
        self._ptr = feat
        self._fdefn = fdefn

    def __del__(self):
        "Releases a reference to this object."
        if self._ptr: destroy_feature(self._ptr)

    def __getitem__(self, index):
        """
        Gets the Field object at the specified index, which may be either
        an integer or the Field's string label.  Note that the Field object
        is not the field's _value_ -- use the `get` method instead to 
        retrieve the value (e.g. an integer) instead of a Field instance.
        """
        if isinstance(index, basestring):
            i = self.index(index)
        else:
            if index < 0 or index > self.num_fields:
                raise OGRIndexError('index out of range')
            i = index
        return Field(self._ptr, i)
    
    def __iter__(self):
        "Iterates over each field in the Feature."
        for i in xrange(self.num_fields):
            yield self[i]

    def __len__(self):
        "Returns the count of fields in this feature."
        return self.num_fields
        
    def __str__(self):
        "The string name of the feature."
        return 'Feature FID %d in Layer<%s>' % (self.fid, self.layer_name)

    def __eq__(self, other):
        "Does equivalence testing on the features."
        return bool(feature_equal(self._ptr, other._ptr))

    #### Feature Properties ####
    @property
    def fid(self):
        "Returns the feature identifier."
        return get_fid(self._ptr)
        
    @property
    def layer_name(self):
        "Returns the name of the layer for the feature."
        return get_feat_name(self._fdefn)

    @property
    def num_fields(self):
        "Returns the number of fields in the Feature."
        return get_feat_field_count(self._ptr)

    @property
    def fields(self):
        "Returns a list of fields in the Feature."
        return [get_field_name(get_field_defn(self._fdefn, i)) 
                for i in xrange(self.num_fields)]

    @property
    def geom(self):
        "Returns the OGR Geometry for this Feature."
        # Retrieving the geometry pointer for the feature.
        geom_ptr = get_feat_geom_ref(self._ptr)
        return OGRGeometry(clone_geom(geom_ptr))

    @property
    def geom_type(self):
        "Returns the OGR Geometry Type for this Feture."
        return OGRGeomType(get_fd_geom_type(self._fdefn))
    
    #### Feature Methods ####
    def get(self, field):
        """
        Returns the value of the field, instead of an instance of the Field
        object.  May take a string of the field name or a Field object as
        parameters.
        """
        field_name = getattr(field, 'name', field)
        return self[field_name].value

    def index(self, field_name):
        "Returns the index of the given field name."
        i = get_field_index(self._ptr, field_name)
        if i < 0: raise OGRIndexError('invalid OFT field name given: "%s"' % field_name)
        return i