python/lib/django_1_4/django/contrib/gis/gdal/field.py

   1 from ctypes import byref, c_int
   2 from datetime import date, datetime, time
   3 from django.contrib.gis.gdal.base import GDALBase
   4 from django.contrib.gis.gdal.error import OGRException
   5 from django.contrib.gis.gdal.prototypes import ds as capi
   6
   7 # For more information, see the OGR C API source code:
   8 #  http://www.gdal.org/ogr/ogr__api_8h.html
   9 #
  10 # The OGR_Fld_* routines are relevant here.
  11 class Field(GDALBase):
  12     "A class that wraps an OGR Field, needs to be instantiated from a Feature object."
  13
  14     #### Python 'magic' routines ####
  15     def __init__(self, feat, index):
  16         """
  17         Initializes on the feature pointer and the integer index of
  18         the field within the feature.
  19         """
  20         # Setting the feature pointer and index.
  21         self._feat = feat
  22         self._index = index
  23
  24         # Getting the pointer for this field.
  25         fld_ptr = capi.get_feat_field_defn(feat, index)
  26         if not fld_ptr:
  27             raise OGRException('Cannot create OGR Field, invalid pointer given.')
  28         self.ptr = fld_ptr
  29
  30         # Setting the class depending upon the OGR Field Type (OFT)
  31         self.__class__ = OGRFieldTypes[self.type]
  32
  33         # OFTReal with no precision should be an OFTInteger.
  34         if isinstance(self, OFTReal) and self.precision == 0:
  35             self.__class__ = OFTInteger
  36             self._double = True
  37
  38     def __str__(self):
  39         "Returns the string representation of the Field."
  40         return str(self.value).strip()
  41
  42     #### Field Methods ####
  43     def as_double(self):
  44         "Retrieves the Field's value as a double (float)."
  45         return capi.get_field_as_double(self._feat, self._index)
  46
  47     def as_int(self):
  48         "Retrieves the Field's value as an integer."
  49         return capi.get_field_as_integer(self._feat, self._index)
  50
  51     def as_string(self):
  52         "Retrieves the Field's value as a string."
  53         return capi.get_field_as_string(self._feat, self._index)
  54
  55     def as_datetime(self):
  56         "Retrieves the Field's value as a tuple of date & time components."
  57         yy, mm, dd, hh, mn, ss, tz = [c_int() for i in range(7)]
  58         status = capi.get_field_as_datetime(self._feat, self._index, byref(yy), byref(mm), byref(dd),
  59                                             byref(hh), byref(mn), byref(ss), byref(tz))
  60         if status:
  61             return (yy, mm, dd, hh, mn, ss, tz)
  62         else:
  63             raise OGRException('Unable to retrieve date & time information from the field.')
  64
  65     #### Field Properties ####
  66     @property
  67     def name(self):
  68         "Returns the name of this Field."
  69         return capi.get_field_name(self.ptr)
  70
  71     @property
  72     def precision(self):
  73         "Returns the precision of this Field."
  74         return capi.get_field_precision(self.ptr)
  75
  76     @property
  77     def type(self):
  78         "Returns the OGR type of this Field."
  79         return capi.get_field_type(self.ptr)
  80
  81     @property
  82     def type_name(self):
  83         "Return the OGR field type name for this Field."
  84         return capi.get_field_type_name(self.type)
  85
  86     @property
  87     def value(self):
  88         "Returns the value of this Field."
  89         # Default is to get the field as a string.
  90         return self.as_string()
  91
  92     @property
  93     def width(self):
  94         "Returns the width of this Field."
  95         return capi.get_field_width(self.ptr)
  96
  97 ### The Field sub-classes for each OGR Field type. ###
  98 class OFTInteger(Field):
  99     _double = False
 100
 101     @property
 102     def value(self):
 103         "Returns an integer contained in this field."
 104         if self._double:
 105             # If this is really from an OFTReal field with no precision,
 106             # read as a double and cast as Python int (to prevent overflow).
 107             return int(self.as_double())
 108         else:
 109             return self.as_int()
 110
 111     @property
 112     def type(self):
 113         """
 114         GDAL uses OFTReals to represent OFTIntegers in created
 115         shapefiles -- forcing the type here since the underlying field
 116         type may actually be OFTReal.
 117         """
 118         return 0
 119
 120 class OFTReal(Field):
 121     @property
 122     def value(self):
 123         "Returns a float contained in this field."
 124         return self.as_double()
 125
 126 # String & Binary fields, just subclasses
 127 class OFTString(Field): pass
 128 class OFTWideString(Field): pass
 129 class OFTBinary(Field): pass
 130
 131 # OFTDate, OFTTime, OFTDateTime fields.
 132 class OFTDate(Field):
 133     @property
 134     def value(self):
 135         "Returns a Python `date` object for the OFTDate field."
 136         try:
 137             yy, mm, dd, hh, mn, ss, tz = self.as_datetime()
 138             return date(yy.value, mm.value, dd.value)
 139         except (ValueError, OGRException):
 140             return None
 141
 142 class OFTDateTime(Field):
 143     @property
 144     def value(self):
 145         "Returns a Python `datetime` object for this OFTDateTime field."
 146         # TODO: Adapt timezone information.
 147         #  See http://lists.osgeo.org/pipermail/gdal-dev/2006-February/007990.html
 148         #  The `tz` variable has values of: 0=unknown, 1=localtime (ambiguous),
 149         #  100=GMT, 104=GMT+1, 80=GMT-5, etc.
 150         try:
 151             yy, mm, dd, hh, mn, ss, tz = self.as_datetime()
 152             return datetime(yy.value, mm.value, dd.value, hh.value, mn.value, ss.value)
 153         except (ValueError, OGRException):
 154             return None
 155
 156 class OFTTime(Field):
 157     @property
 158     def value(self):
 159         "Returns a Python `time` object for this OFTTime field."
 160         try:
 161             yy, mm, dd, hh, mn, ss, tz = self.as_datetime()
 162             return time(hh.value, mn.value, ss.value)
 163         except (ValueError, OGRException):
 164             return None
 165
 166 # List fields are also just subclasses
 167 class OFTIntegerList(Field): pass
 168 class OFTRealList(Field): pass
 169 class OFTStringList(Field): pass
 170 class OFTWideStringList(Field): pass
 171
 172 # Class mapping dictionary for OFT Types and reverse mapping.
 173 OGRFieldTypes = { 0 : OFTInteger,
 174                   1 : OFTIntegerList,
 175                   2 : OFTReal,
 176                   3 : OFTRealList,
 177                   4 : OFTString,
 178                   5 : OFTStringList,
 179                   6 : OFTWideString,
 180                   7 : OFTWideStringList,
 181                   8 : OFTBinary,
 182                   9 : OFTDate,
 183                  10 : OFTTime,
 184                  11 : OFTDateTime,
 185                   }
 186 ROGRFieldTypes = dict([(cls, num) for num, cls in OGRFieldTypes.items()])