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srs.py
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"""
The Spatial Reference class, represents OGR Spatial Reference objects.
Example:
>>> from django.contrib.gis.gdal import SpatialReference
>>> srs = SpatialReference('WGS84')
>>> print(srs)
GEOGCS["WGS 84",
DATUM["WGS_1984",
SPHEROID["WGS 84",6378137,298.257223563,
AUTHORITY["EPSG","7030"]],
TOWGS84[0,0,0,0,0,0,0],
AUTHORITY["EPSG","6326"]],
PRIMEM["Greenwich",0,
AUTHORITY["EPSG","8901"]],
UNIT["degree",0.01745329251994328,
AUTHORITY["EPSG","9122"]],
AUTHORITY["EPSG","4326"]]
>>> print(srs.proj)
+proj=longlat +ellps=WGS84 +datum=WGS84 +no_defs
>>> print(srs.ellipsoid)
(6378137.0, 6356752.3142451793, 298.25722356300003)
>>> print(srs.projected, srs.geographic)
False True
>>> srs.import_epsg(32140)
>>> print(srs.name)
NAD83 / Texas South Central
"""
from ctypes import byref, c_char_p, c_int
from enum import IntEnum
from types import NoneType
from django.contrib.gis.gdal.base import GDALBase
from django.contrib.gis.gdal.error import SRSException
from django.contrib.gis.gdal.prototypes import srs as capi
from django.utils.encoding import force_bytes, force_str
class AxisOrder(IntEnum):
TRADITIONAL = 0
AUTHORITY = 1
class SpatialReference(GDALBase):
"""
A wrapper for the OGRSpatialReference object. According to the GDAL web
site, the SpatialReference object "provide[s] services to represent
coordinate systems (projections and datums) and to transform between them."
"""
destructor = capi.release_srs
def __init__(self, srs_input="", srs_type="user", axis_order=None):
"""
Create a GDAL OSR Spatial Reference object from the given input.
The input may be string of OGC Well Known Text (WKT), an integer
EPSG code, a PROJ string, and/or a projection "well known" shorthand
string (one of 'WGS84', 'WGS72', 'NAD27', 'NAD83').
"""
if not isinstance(axis_order, (NoneType, AxisOrder)):
raise ValueError(
"SpatialReference.axis_order must be an AxisOrder instance."
)
self.axis_order = axis_order or AxisOrder.TRADITIONAL
if srs_type == "wkt":
self.ptr = capi.new_srs(c_char_p(b""))
self.import_wkt(srs_input)
if self.axis_order == AxisOrder.TRADITIONAL:
capi.set_axis_strategy(self.ptr, self.axis_order)
return
elif isinstance(srs_input, str):
try:
# If SRID is a string, e.g., '4326', then make acceptable
# as user input.
srid = int(srs_input)
srs_input = "EPSG:%d" % srid
except ValueError:
pass
elif isinstance(srs_input, int):
# EPSG integer code was input.
srs_type = "epsg"
elif isinstance(srs_input, self.ptr_type):
srs = srs_input
srs_type = "ogr"
else:
raise TypeError('Invalid SRS type "%s"' % srs_type)
if srs_type == "ogr":
# Input is already an SRS pointer.
srs = srs_input
else:
# Creating a new SRS pointer, using the string buffer.
buf = c_char_p(b"")
srs = capi.new_srs(buf)
# If the pointer is NULL, throw an exception.
if not srs:
raise SRSException(
"Could not create spatial reference from: %s" % srs_input
)
else:
self.ptr = srs
if self.axis_order == AxisOrder.TRADITIONAL:
capi.set_axis_strategy(self.ptr, self.axis_order)
# Importing from either the user input string or an integer SRID.
if srs_type == "user":
self.import_user_input(srs_input)
elif srs_type == "epsg":
self.import_epsg(srs_input)
def __getitem__(self, target):
"""
Return the value of the given string attribute node, None if the node
doesn't exist. Can also take a tuple as a parameter, (target, child),
where child is the index of the attribute in the WKT. For example:
>>> wkt = (
... 'GEOGCS["WGS 84",'
... ' DATUM["WGS_1984, ... AUTHORITY["EPSG","4326"]'
... ']'
... )
>>> srs = SpatialReference(wkt) # could also use 'WGS84', or 4326
>>> print(srs['GEOGCS'])
WGS 84
>>> print(srs['DATUM'])
WGS_1984
>>> print(srs['AUTHORITY'])
EPSG
>>> print(srs['AUTHORITY', 1]) # The authority value
4326
>>> print(srs['TOWGS84', 4]) # the fourth value in this wkt
0
>>> # For the units authority, have to use the pipe symbole.
>>> print(srs['UNIT|AUTHORITY'])
EPSG
>>> print(srs['UNIT|AUTHORITY', 1]) # The authority value for the units
9122
"""
if isinstance(target, tuple):
return self.attr_value(*target)
else:
return self.attr_value(target)
def __str__(self):
"Use 'pretty' WKT."
return self.pretty_wkt
# #### SpatialReference Methods ####
def attr_value(self, target, index=0):
"""
The attribute value for the given target node (e.g. 'PROJCS'). The
index keyword specifies an index of the child node to return.
"""
if not isinstance(target, str) or not isinstance(index, int):
raise TypeError
return capi.get_attr_value(self.ptr, force_bytes(target), index)
def auth_name(self, target):
"Return the authority name for the given string target node."
return capi.get_auth_name(
self.ptr, target if target is None else force_bytes(target)
)
def auth_code(self, target):
"Return the authority code for the given string target node."
return capi.get_auth_code(
self.ptr, target if target is None else force_bytes(target)
)
def clone(self):
"Return a clone of this SpatialReference object."
return SpatialReference(capi.clone_srs(self.ptr), axis_order=self.axis_order)
def from_esri(self):
"Morph this SpatialReference from ESRI's format to EPSG."
capi.morph_from_esri(self.ptr)
def identify_epsg(self):
"""
This method inspects the WKT of this SpatialReference, and will
add EPSG authority nodes where an EPSG identifier is applicable.
"""
capi.identify_epsg(self.ptr)
def to_esri(self):
"Morph this SpatialReference to ESRI's format."
capi.morph_to_esri(self.ptr)
def validate(self):
"Check to see if the given spatial reference is valid."
capi.srs_validate(self.ptr)
# #### Name & SRID properties ####
@property
def name(self):
"Return the name of this Spatial Reference."
if self.projected:
return self.attr_value("PROJCS")
elif self.geographic:
return self.attr_value("GEOGCS")
elif self.local:
return self.attr_value("LOCAL_CS")
else:
return None
@property
def srid(self):
"Return the SRID of top-level authority, or None if undefined."
try:
return int(self.auth_code(target=None))
except (TypeError, ValueError):
return None
# #### Unit Properties ####
@property
def linear_name(self):
"Return the name of the linear units."
units, name = capi.linear_units(self.ptr, byref(c_char_p()))
return name
@property
def linear_units(self):
"Return the value of the linear units."
units, name = capi.linear_units(self.ptr, byref(c_char_p()))
return units
@property
def angular_name(self):
"Return the name of the angular units."
units, name = capi.angular_units(self.ptr, byref(c_char_p()))
return name
@property
def angular_units(self):
"Return the value of the angular units."
units, name = capi.angular_units(self.ptr, byref(c_char_p()))
return units
@property
def units(self):
"""
Return a 2-tuple of the units value and the units name. Automatically
determine whether to return the linear or angular units.
"""
units, name = None, None
if self.projected or self.local:
units, name = capi.linear_units(self.ptr, byref(c_char_p()))
elif self.geographic:
units, name = capi.angular_units(self.ptr, byref(c_char_p()))
if name is not None:
name = force_str(name)
return (units, name)
# #### Spheroid/Ellipsoid Properties ####
@property
def ellipsoid(self):
"""
Return a tuple of the ellipsoid parameters:
(semimajor axis, semiminor axis, and inverse flattening)
"""
return (self.semi_major, self.semi_minor, self.inverse_flattening)
@property
def semi_major(self):
"Return the Semi Major Axis for this Spatial Reference."
return capi.semi_major(self.ptr, byref(c_int()))
@property
def semi_minor(self):
"Return the Semi Minor Axis for this Spatial Reference."
return capi.semi_minor(self.ptr, byref(c_int()))
@property
def inverse_flattening(self):
"Return the Inverse Flattening for this Spatial Reference."
return capi.invflattening(self.ptr, byref(c_int()))
# #### Boolean Properties ####
@property
def geographic(self):
"""
Return True if this SpatialReference is geographic
(root node is GEOGCS).
"""
return bool(capi.isgeographic(self.ptr))
@property
def local(self):
"""
Return True if this SpatialReference is local (root node is LOCAL_CS).
"""
return bool(capi.islocal(self.ptr))
@property
def projected(self):
"""
Return True if this SpatialReference is a projected coordinate system
(root node is PROJCS).
"""
return bool(capi.isprojected(self.ptr))
# #### Import Routines #####
def import_epsg(self, epsg):
"Import the Spatial Reference from the EPSG code (an integer)."
capi.from_epsg(self.ptr, epsg)
def import_proj(self, proj):
"""Import the Spatial Reference from a PROJ string."""
capi.from_proj(self.ptr, proj)
def import_user_input(self, user_input):
"Import the Spatial Reference from the given user input string."
capi.from_user_input(self.ptr, force_bytes(user_input))
def import_wkt(self, wkt):
"Import the Spatial Reference from OGC WKT (string)"
capi.from_wkt(self.ptr, byref(c_char_p(force_bytes(wkt))))
def import_xml(self, xml):
"Import the Spatial Reference from an XML string."
capi.from_xml(self.ptr, xml)
# #### Export Properties ####
@property
def wkt(self):
"Return the WKT representation of this Spatial Reference."
return capi.to_wkt(self.ptr, byref(c_char_p()))
@property
def pretty_wkt(self, simplify=0):
"Return the 'pretty' representation of the WKT."
return capi.to_pretty_wkt(self.ptr, byref(c_char_p()), simplify)
@property
def proj(self):
"""Return the PROJ representation for this Spatial Reference."""
return capi.to_proj(self.ptr, byref(c_char_p()))
@property
def proj4(self):
"Alias for proj()."
return self.proj
@property
def xml(self, dialect=""):
"Return the XML representation of this Spatial Reference."
return capi.to_xml(self.ptr, byref(c_char_p()), force_bytes(dialect))
class CoordTransform(GDALBase):
"The coordinate system transformation object."
destructor = capi.destroy_ct
def __init__(self, source, target):
"Initialize on a source and target SpatialReference objects."
if not isinstance(source, SpatialReference) or not isinstance(
target, SpatialReference
):
raise TypeError("source and target must be of type SpatialReference")
self.ptr = capi.new_ct(source._ptr, target._ptr)
self._srs1_name = source.name
self._srs2_name = target.name
def __str__(self):
return 'Transform from "%s" to "%s"' % (self._srs1_name, self._srs2_name)