1 # The GDAL C library, OGR exception, and the Field object

     2 from django.contrib.gis.gdal.base import GDALBase

     3 from django.contrib.gis.gdal.error import OGRException, OGRIndexError

     4 from django.contrib.gis.gdal.field import Field

     5 from django.contrib.gis.gdal.geometries import OGRGeometry, OGRGeomType

     6 from django.contrib.gis.gdal.srs import SpatialReference

     7 

     8 # ctypes function prototypes

     9 from django.contrib.gis.gdal.prototypes import ds as capi, geom as geom_api

    10 

    11 # For more information, see the OGR C API source code:

    12 #  http://www.gdal.org/ogr/ogr__api_8h.html

    13 #

    14 # The OGR_F_* routines are relevant here.

    15 class Feature(GDALBase):

    16     "A class that wraps an OGR Feature, needs to be instantiated from a Layer object."

    17 

    18     #### Python 'magic' routines ####

    19     def __init__(self, feat, fdefn):

    20         "Initializes on the pointers for the feature and the layer definition."

    21         if not feat or not fdefn:

    22             raise OGRException('Cannot create OGR Feature, invalid pointer given.')

    23         self.ptr = feat

    24         self._fdefn = fdefn

    25 

    26     def __del__(self):

    27         "Releases a reference to this object."

    28         if self._ptr: capi.destroy_feature(self._ptr)

    29 

    30     def __getitem__(self, index):

    31         """

    32         Gets the Field object at the specified index, which may be either

    33         an integer or the Field's string label.  Note that the Field object

    34         is not the field's _value_ -- use the `get` method instead to 

    35         retrieve the value (e.g. an integer) instead of a Field instance.

    36         """

    37         if isinstance(index, basestring):

    38             i = self.index(index)

    39         else:

    40             if index < 0 or index > self.num_fields:

    41                 raise OGRIndexError('index out of range')

    42             i = index

    43         return Field(self.ptr, i)

    44     

    45     def __iter__(self):

    46         "Iterates over each field in the Feature."

    47         for i in xrange(self.num_fields):

    48             yield self[i]

    49 

    50     def __len__(self):

    51         "Returns the count of fields in this feature."

    52         return self.num_fields

    53         

    54     def __str__(self):

    55         "The string name of the feature."

    56         return 'Feature FID %d in Layer<%s>' % (self.fid, self.layer_name)

    57 

    58     def __eq__(self, other):

    59         "Does equivalence testing on the features."

    60         return bool(capi.feature_equal(self.ptr, other._ptr))

    61 

    62     #### Feature Properties ####

    63     @property

    64     def fid(self):

    65         "Returns the feature identifier."

    66         return capi.get_fid(self.ptr)

    67         

    68     @property

    69     def layer_name(self):

    70         "Returns the name of the layer for the feature."

    71         return capi.get_feat_name(self._fdefn)

    72 

    73     @property

    74     def num_fields(self):

    75         "Returns the number of fields in the Feature."

    76         return capi.get_feat_field_count(self.ptr)

    77 

    78     @property

    79     def fields(self):

    80         "Returns a list of fields in the Feature."

    81         return [capi.get_field_name(capi.get_field_defn(self._fdefn, i)) 

    82                 for i in xrange(self.num_fields)]

    83 

    84     @property

    85     def geom(self):

    86         "Returns the OGR Geometry for this Feature."

    87         # Retrieving the geometry pointer for the feature.

    88         geom_ptr = capi.get_feat_geom_ref(self.ptr)

    89         return OGRGeometry(geom_api.clone_geom(geom_ptr))

    90 

    91     @property

    92     def geom_type(self):

    93         "Returns the OGR Geometry Type for this Feture."

    94         return OGRGeomType(capi.get_fd_geom_type(self._fdefn))

    95     

    96     #### Feature Methods ####

    97     def get(self, field):

    98         """

    99         Returns the value of the field, instead of an instance of the Field

   100         object.  May take a string of the field name or a Field object as

   101         parameters.

   102         """

   103         field_name = getattr(field, 'name', field)

   104         return self[field_name].value

   105 

   106     def index(self, field_name):

   107         "Returns the index of the given field name."

   108         i = capi.get_field_index(self.ptr, field_name)

   109         if i < 0: raise OGRIndexError('invalid OFT field name given: "%s"' % field_name)

   110         return i