from ctypes import byref, c_int from datetime import date, datetime, time from django.contrib.gis.gdal.base import GDALBase from django.contrib.gis.gdal.error import OGRException from django.contrib.gis.gdal.prototypes import ds as capi from django.utils.encoding import force_text # For more information, see the OGR C API source code: # http://www.gdal.org/ogr/ogr__api_8h.html # # The OGR_Fld_* routines are relevant here. class Field(GDALBase): """ This class wraps an OGR Field, and needs to be instantiated from a Feature object. """ #### Python 'magic' routines #### def __init__(self, feat, index): """ Initializes on the feature object and the integer index of the field within the feature. """ # Setting the feature pointer and index. self._feat = feat self._index = index # Getting the pointer for this field. fld_ptr = capi.get_feat_field_defn(feat.ptr, index) if not fld_ptr: raise OGRException('Cannot create OGR Field, invalid pointer given.') self.ptr = fld_ptr # Setting the class depending upon the OGR Field Type (OFT) self.__class__ = OGRFieldTypes[self.type] # OFTReal with no precision should be an OFTInteger. if isinstance(self, OFTReal) and self.precision == 0: self.__class__ = OFTInteger self._double = True def __str__(self): "Returns the string representation of the Field." return str(self.value).strip() #### Field Methods #### def as_double(self): "Retrieves the Field's value as a double (float)." return capi.get_field_as_double(self._feat.ptr, self._index) def as_int(self): "Retrieves the Field's value as an integer." return capi.get_field_as_integer(self._feat.ptr, self._index) def as_string(self): "Retrieves the Field's value as a string." string = capi.get_field_as_string(self._feat.ptr, self._index) return force_text(string, encoding=self._feat.encoding, strings_only=True) def as_datetime(self): "Retrieves the Field's value as a tuple of date & time components." yy, mm, dd, hh, mn, ss, tz = [c_int() for i in range(7)] status = capi.get_field_as_datetime( self._feat.ptr, self._index, byref(yy), byref(mm), byref(dd), byref(hh), byref(mn), byref(ss), byref(tz)) if status: return (yy, mm, dd, hh, mn, ss, tz) else: raise OGRException('Unable to retrieve date & time information from the field.') #### Field Properties #### @property def name(self): "Returns the name of this Field." name = capi.get_field_name(self.ptr) return force_text(name, encoding=self._feat.encoding, strings_only=True) @property def precision(self): "Returns the precision of this Field." return capi.get_field_precision(self.ptr) @property def type(self): "Returns the OGR type of this Field." return capi.get_field_type(self.ptr) @property def type_name(self): "Return the OGR field type name for this Field." return capi.get_field_type_name(self.type) @property def value(self): "Returns the value of this Field." # Default is to get the field as a string. return self.as_string() @property def width(self): "Returns the width of this Field." return capi.get_field_width(self.ptr) ### The Field sub-classes for each OGR Field type. ### class OFTInteger(Field): _double = False @property def value(self): "Returns an integer contained in this field." if self._double: # If this is really from an OFTReal field with no precision, # read as a double and cast as Python int (to prevent overflow). return int(self.as_double()) else: return self.as_int() @property def type(self): """ GDAL uses OFTReals to represent OFTIntegers in created shapefiles -- forcing the type here since the underlying field type may actually be OFTReal. """ return 0 class OFTReal(Field): @property def value(self): "Returns a float contained in this field." return self.as_double() # String & Binary fields, just subclasses class OFTString(Field): pass class OFTWideString(Field): pass class OFTBinary(Field): pass # OFTDate, OFTTime, OFTDateTime fields. class OFTDate(Field): @property def value(self): "Returns a Python `date` object for the OFTDate field." try: yy, mm, dd, hh, mn, ss, tz = self.as_datetime() return date(yy.value, mm.value, dd.value) except (ValueError, OGRException): return None class OFTDateTime(Field): @property def value(self): "Returns a Python `datetime` object for this OFTDateTime field." # TODO: Adapt timezone information. # See http://lists.osgeo.org/pipermail/gdal-dev/2006-February/007990.html # The `tz` variable has values of: 0=unknown, 1=localtime (ambiguous), # 100=GMT, 104=GMT+1, 80=GMT-5, etc. try: yy, mm, dd, hh, mn, ss, tz = self.as_datetime() return datetime(yy.value, mm.value, dd.value, hh.value, mn.value, ss.value) except (ValueError, OGRException): return None class OFTTime(Field): @property def value(self): "Returns a Python `time` object for this OFTTime field." try: yy, mm, dd, hh, mn, ss, tz = self.as_datetime() return time(hh.value, mn.value, ss.value) except (ValueError, OGRException): return None # List fields are also just subclasses class OFTIntegerList(Field): pass class OFTRealList(Field): pass class OFTStringList(Field): pass class OFTWideStringList(Field): pass # Class mapping dictionary for OFT Types and reverse mapping. OGRFieldTypes = { 0: OFTInteger, 1: OFTIntegerList, 2: OFTReal, 3: OFTRealList, 4: OFTString, 5: OFTStringList, 6: OFTWideString, 7: OFTWideStringList, 8: OFTBinary, 9: OFTDate, 10: OFTTime, 11: OFTDateTime, } ROGRFieldTypes = dict((cls, num) for num, cls in OGRFieldTypes.items())