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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()])
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