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

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

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

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

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

     6 

     7 # ctypes function prototypes

     8 from django.contrib.gis.gdal.prototypes.ds import \

     9     destroy_feature, feature_equal, get_fd_geom_type, get_feat_geom_ref, \

    10     get_feat_name, get_feat_field_count, get_fid, get_field_defn, \

    11     get_field_index, get_field_name

    12 from django.contrib.gis.gdal.prototypes.geom import clone_geom, get_geom_srs

    13 from django.contrib.gis.gdal.prototypes.srs import clone_srs

    14 

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

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

    17 #

    18 # The OGR_F_* routines are relevant here.

    19 class Feature(object):

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

    21 

    22     #### Python 'magic' routines ####

    23     def __init__(self, feat, fdefn):

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

    25         self._ptr = None # Initially NULL

    26         if not feat or not fdefn:

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

    28         self._ptr = feat

    29         self._fdefn = fdefn

    30 

    31     def __del__(self):

    32         "Releases a reference to this object."

    33         if self._ptr: destroy_feature(self._ptr)

    34 

    35     def __getitem__(self, index):

    36         """

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

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

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

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

    41         """

    42         if isinstance(index, basestring):

    43             i = self.index(index)

    44         else:

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

    46                 raise OGRIndexError('index out of range')

    47             i = index

    48         return Field(self._ptr, i)

    49     

    50     def __iter__(self):

    51         "Iterates over each field in the Feature."

    52         for i in xrange(self.num_fields):

    53             yield self[i]

    54 

    55     def __len__(self):

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

    57         return self.num_fields

    58         

    59     def __str__(self):

    60         "The string name of the feature."

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

    62 

    63     def __eq__(self, other):

    64         "Does equivalence testing on the features."

    65         return bool(feature_equal(self._ptr, other._ptr))

    66 

    67     #### Feature Properties ####

    68     @property

    69     def fid(self):

    70         "Returns the feature identifier."

    71         return get_fid(self._ptr)

    72         

    73     @property

    74     def layer_name(self):

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

    76         return get_feat_name(self._fdefn)

    77 

    78     @property

    79     def num_fields(self):

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

    81         return get_feat_field_count(self._ptr)

    82 

    83     @property

    84     def fields(self):

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

    86         return [get_field_name(get_field_defn(self._fdefn, i)) 

    87                 for i in xrange(self.num_fields)]

    88 

    89     @property

    90     def geom(self):

    91         "Returns the OGR Geometry for this Feature."

    92         # Retrieving the geometry pointer for the feature.

    93         geom_ptr = get_feat_geom_ref(self._ptr)

    94         return OGRGeometry(clone_geom(geom_ptr))

    95 

    96     @property

    97     def geom_type(self):

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

    99         return OGRGeomType(get_fd_geom_type(self._fdefn))

   100     

   101     #### Feature Methods ####

   102     def get(self, field):

   103         """

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

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

   106         parameters.

   107         """

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

   109         return self[field_name].value

   110 

   111     def index(self, field_name):

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

   113         i = get_field_index(self._ptr, field_name)

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

   115         return i