/usr/lib/python2.7/dist-packages/cartopy/io/ogc_clients.py is in python-cartopy 0.14.2+dfsg1-2build3.
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#
# This file is part of cartopy.
#
# cartopy is free software: you can redistribute it and/or modify it under
# the terms of the GNU Lesser General Public License as published by the
# Free Software Foundation, either version 3 of the License, or
# (at your option) any later version.
#
# cartopy is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
# GNU Lesser General Public License for more details.
#
# You should have received a copy of the GNU Lesser General Public License
# along with cartopy. If not, see <https://www.gnu.org/licenses/>.
"""
Implements RasterSource classes which can retrieve imagery from web services
such as WMS and WMTS.
The matplotlib interface can make use of RasterSources via the
:meth:`cartopy.mpl.geoaxes.GeoAxes.add_raster` method,
with additional specific methods which make use of this for WMS and WMTS
(:meth:`~cartopy.mpl.geoaxes.GeoAxes.add_wms` and
:meth:`~cartopy.mpl.geoaxes.GeoAxes.add_wmts`). An example of using WMTS in
this way can be found at :ref:`examples-wmts`.
"""
from __future__ import (absolute_import, division, print_function)
import six
import collections
import io
import math
import warnings
import weakref
from xml.etree import ElementTree
import numpy as np
from PIL import Image
import shapely.geometry as sgeom
try:
from owslib.wms import WebMapService
from owslib.wfs import WebFeatureService
import owslib.util
import owslib.wmts
_OWSLIB_AVAILABLE = True
except ImportError:
WebMapService = None
WebFeatureService = None
_OWSLIB_AVAILABLE = False
import cartopy.crs as ccrs
from cartopy.io import LocatedImage, RasterSource
from cartopy.img_transform import warp_array
_OWSLIB_REQUIRED = 'OWSLib is required to use OGC web services.'
# Hardcode some known EPSG codes for now.
# The order given here determines the preferred SRS for WMS retrievals.
_CRS_TO_OGC_SRS = collections.OrderedDict(
[(ccrs.PlateCarree(), 'EPSG:4326'),
(ccrs.Mercator.GOOGLE, 'EPSG:900913')])
# Standard pixel size of 0.28 mm as defined by WMTS.
METERS_PER_PIXEL = 0.28e-3
_WGS84_METERS_PER_UNIT = 2 * math.pi * 6378137 / 360
METERS_PER_UNIT = {
'urn:ogc:def:crs:EPSG::27700': 1,
'urn:ogc:def:crs:EPSG::900913': 1,
'urn:ogc:def:crs:OGC:1.3:CRS84': _WGS84_METERS_PER_UNIT,
}
_URN_TO_CRS = {
'urn:ogc:def:crs:EPSG::27700': ccrs.OSGB(),
'urn:ogc:def:crs:EPSG::4326': ccrs.PlateCarree(),
'urn:ogc:def:crs:EPSG::900913': ccrs.GOOGLE_MERCATOR,
'urn:ogc:def:crs:OGC:1.3:CRS84': ccrs.PlateCarree(),
'urn:ogc:def:crs:EPSG::3031': ccrs.Stereographic(central_latitude=-90,
true_scale_latitude=-71)
}
# XML namespace definitions
_MAP_SERVER_NS = '{http://mapserver.gis.umn.edu/mapserver}'
_GML_NS = '{http://www.opengis.net/gml}'
class WMSRasterSource(RasterSource):
"""
A WMS imagery retriever which can be added to a map.
.. note:: Requires owslib and Pillow to work.
.. note::
No caching of retrieved maps is done with this WMSRasterSource.
To reduce load on the WMS server it is encouraged to tile
map requests and subsequently stitch them together to recreate
a single raster, thus allowing for a more aggressive caching scheme,
but this WMSRasterSource does not currently implement WMS tile
fetching.
Whilst not the same service, there is also a WMTSRasterSource which
makes use of tiles and comes with built-in caching for fast repeated
map retrievals.
"""
def __init__(self, service, layers, getmap_extra_kwargs=None):
"""
Parameters
----------
service : string or WebMapService instance
The WebMapService instance, or URL of a WMS service, from whence
to retrieve the image.
layers : string or list of strings
The name(s) of layers to use from the WMS service.
getmap_extra_kwargs : dict or None
Extra keywords to pass through to the service's getmap method.
If None, a dictionary with ``{'transparent': True}`` will
be defined.
"""
if WebMapService is None:
raise ImportError(_OWSLIB_REQUIRED)
if isinstance(service, six.string_types):
service = WebMapService(service)
if isinstance(layers, six.string_types):
layers = [layers]
if getmap_extra_kwargs is None:
getmap_extra_kwargs = {'transparent': True}
if len(layers) == 0:
raise ValueError('One or more layers must be defined.')
for layer in layers:
if layer not in service.contents:
raise ValueError('The {!r} layer does not exist in '
'this service.'.format(layer))
#: The OWSLib WebMapService instance.
self.service = service
#: The names of the layers to fetch.
self.layers = layers
#: Extra kwargs passed through to the service's getmap request.
self.getmap_extra_kwargs = getmap_extra_kwargs
def _native_srs(self, projection):
# Return the SRS which corresponds to the given projection when
# known, otherwise return None.
return _CRS_TO_OGC_SRS.get(projection)
def _fallback_proj_and_srs(self):
"""
Return a :class:`cartopy.crs.Projection` and corresponding
SRS string in which the WMS service can supply the requested
layers.
"""
contents = self.service.contents
for proj, srs in six.iteritems(_CRS_TO_OGC_SRS):
missing = any(srs not in contents[layer].crsOptions for
layer in self.layers)
if not missing:
break
if missing:
raise ValueError('The requested layers are not available in a '
'known SRS.')
return proj, srs
def validate_projection(self, projection):
if self._native_srs(projection) is None:
self._fallback_proj_and_srs()
def _image_and_extent(self, wms_proj, wms_srs, wms_extent, output_proj,
output_extent, target_resolution):
min_x, max_x, min_y, max_y = wms_extent
wms_image = self.service.getmap(layers=self.layers,
srs=wms_srs,
bbox=(min_x, min_y, max_x, max_y),
size=target_resolution,
format='image/png',
**self.getmap_extra_kwargs)
wms_image = Image.open(io.BytesIO(wms_image.read()))
if wms_proj == output_proj:
extent = output_extent
else:
# Convert Image to numpy array (flipping so that origin
# is 'lower').
img, extent = warp_array(np.asanyarray(wms_image)[::-1],
source_proj=wms_proj,
source_extent=wms_extent,
target_proj=output_proj,
target_res=target_resolution,
target_extent=output_extent,
mask_extrapolated=True)
# Convert arrays with masked RGB(A) values to non-masked RGBA
# arrays, setting the alpha channel to zero for masked values.
# This avoids unsightly grey boundaries appearing when the
# extent is limited (i.e. not global).
if np.ma.is_masked(img):
if img.shape[2:3] == (3,):
# RGB
old_img = img
img = np.zeros(img.shape[:2] + (4,), dtype=img.dtype)
img[:, :, 0:3] = old_img
img[:, :, 3] = ~ np.any(old_img.mask, axis=2)
if img.dtype.kind == 'u':
img[:, :, 3] *= 255
elif img.shape[2:3] == (4,):
# RGBA
img[:, :, 3] = np.where(np.any(img.mask, axis=2), 0,
img[:, :, 3])
img = img.data
# Convert warped image array back to an Image, undoing the
# earlier flip.
wms_image = Image.fromarray(img[::-1])
return LocatedImage(wms_image, extent)
def fetch_raster(self, projection, extent, target_resolution):
min_x, max_x, min_y, max_y = extent
target_resolution = [int(np.ceil(val)) for val in target_resolution]
wms_srs = self._native_srs(projection)
if wms_srs is not None:
wms_proj = projection
wms_extents = [extent]
else:
# The SRS for the requested projection is not known, so
# attempt to use the fallback and perform the necessary
# transformations.
wms_proj, wms_srs = self._fallback_proj_and_srs()
# Calculate the bounding box(es) in WMS projection.
# Start with the requested area.
target_box = sgeom.box(min_x, min_y, max_x, max_y)
# If the requested area (i.e. target_box) is bigger (or
# nearly bigger) than the entire output projection domain
# then we erode the request area to avoid re-projection
# instabilities near the full-projection limit.
buffered_target_box = target_box.buffer(projection.threshold,
resolution=1)
fudge_mode = buffered_target_box.contains(projection.domain)
if fudge_mode:
target_box = projection.domain.buffer(-projection.threshold)
# Convert the requested area to the WMS server's projection.
wms_polys = wms_proj.project_geometry(target_box, projection)
wms_extents = []
for wms_poly in wms_polys:
min_x, min_y, max_x, max_y = wms_poly.bounds
if fudge_mode:
# If we shrunk the request area before, then here we
# need to re-inflate.
radius = min(max_x - min_x, max_y - min_y) / 5.0
radius = min(radius, wms_proj.threshold * 15)
wms_poly = wms_poly.buffer(radius, resolution=1)
# Prevent the expanded request going beyond the
# limits of the projection.
wms_poly = wms_proj.domain.intersection(wms_poly)
min_x, min_y, max_x, max_y = wms_poly.bounds
wms_extents.append((min_x, max_x, min_y, max_y))
located_images = []
for wms_extent in wms_extents:
located_images.append(self._image_and_extent(wms_proj, wms_srs,
wms_extent,
projection, extent,
target_resolution))
return located_images
class WMTSRasterSource(RasterSource):
"""
A WMTS imagery retriever which can be added to a map.
Uses tile caching for fast repeated map retrievals.
.. note:: Requires owslib and Pillow to work.
"""
_shared_image_cache = weakref.WeakKeyDictionary()
"""
A nested mapping from WMTS, layer name, tile matrix name, tile row
and tile column to the resulting PIL image::
{wmts: {(layer_name, tile_matrix_name): {(row, column): Image}}}
This provides a significant boost when producing multiple maps of the
same projection or with an interactive figure.
"""
def __init__(self, wmts, layer_name):
"""
Args:
* wmts - The URL of the WMTS, or an
owslib.wmts.WebMapTileService instance.
* layer_name - The name of the layer to use.
"""
if WebMapService is None:
raise ImportError(_OWSLIB_REQUIRED)
if not (hasattr(wmts, 'tilematrixsets') and
hasattr(wmts, 'contents') and
hasattr(wmts, 'gettile')):
wmts = owslib.wmts.WebMapTileService(wmts)
try:
layer = wmts.contents[layer_name]
except KeyError:
raise ValueError('Invalid layer name {!r} for WMTS at {!r}'.format(
layer_name, wmts.url))
#: The OWSLib WebMapTileService instance.
self.wmts = wmts
#: The layer to fetch.
self.layer = layer
self._matrix_set_name_map = {}
def _matrix_set_name(self, projection):
key = id(projection)
matrix_set_name = self._matrix_set_name_map.get(key)
if matrix_set_name is None:
wmts = self.wmts
if hasattr(self.layer, 'tilematrixsetlinks'):
matrix_set_names = self.layer.tilematrixsetlinks.keys()
else:
matrix_set_names = self.layer.tilematrixsets
for tile_matrix_set_name in matrix_set_names:
tile_matrix_set = wmts.tilematrixsets[tile_matrix_set_name]
crs_urn = tile_matrix_set.crs
if crs_urn in _URN_TO_CRS:
tms_crs = _URN_TO_CRS[crs_urn]
if tms_crs == projection:
matrix_set_name = tile_matrix_set_name
break
if matrix_set_name is None:
available_urns = sorted(set(
wmts.tilematrixsets[name].crs for name in
matrix_set_names))
msg = 'Unable to find tile matrix for projection.'
msg += '\n Projection: ' + str(projection)
msg += '\n Available tile CRS URNs:'
msg += '\n ' + '\n '.join(available_urns)
raise ValueError(msg)
self._matrix_set_name_map[key] = matrix_set_name
return matrix_set_name
def validate_projection(self, projection):
self._matrix_set_name(projection)
def fetch_raster(self, projection, extent, target_resolution):
matrix_set_name = self._matrix_set_name(projection)
min_x, max_x, min_y, max_y = extent
width, height = target_resolution
max_pixel_span = min((max_x - min_x) / width,
(max_y - min_y) / height)
image, extent = self._wmts_images(self.wmts, self.layer,
matrix_set_name, extent,
max_pixel_span)
return [LocatedImage(image, extent)]
def _choose_matrix(self, tile_matrices, meters_per_unit, max_pixel_span):
# Get the tile matrices in order of increasing resolution.
tile_matrices = sorted(tile_matrices,
key=lambda tm: tm.scaledenominator,
reverse=True)
# Find which tile matrix has the appropriate resolution.
max_scale = max_pixel_span * meters_per_unit / METERS_PER_PIXEL
for tm in tile_matrices:
if tm.scaledenominator <= max_scale:
return tm
return tile_matrices[-1]
def _tile_span(self, tile_matrix, meters_per_unit):
pixel_span = tile_matrix.scaledenominator * (
METERS_PER_PIXEL / meters_per_unit)
tile_span_x = tile_matrix.tilewidth * pixel_span
tile_span_y = tile_matrix.tileheight * pixel_span
return tile_span_x, tile_span_y
def _select_tiles(self, tile_matrix, tile_matrix_limits,
tile_span_x, tile_span_y, extent):
# Convert the requested extent from CRS coordinates to tile
# indices. See annex H of the WMTS v1.0.0 spec.
# NB. The epsilons get rid of any tiles which only just
# (i.e. one part in a million) intrude into the requested
# extent. Since these wouldn't be visible anyway there's nothing
# to be gained by spending the time downloading them.
min_x, max_x, min_y, max_y = extent
matrix_min_x, matrix_max_y = tile_matrix.topleftcorner
epsilon = 1e-6
min_col = int((min_x - matrix_min_x) / tile_span_x + epsilon)
max_col = int((max_x - matrix_min_x) / tile_span_x - epsilon)
min_row = int((matrix_max_y - max_y) / tile_span_y + epsilon)
max_row = int((matrix_max_y - min_y) / tile_span_y - epsilon)
# Clamp to the limits of the tile matrix.
min_col = max(min_col, 0)
max_col = min(max_col, tile_matrix.matrixwidth - 1)
min_row = max(min_row, 0)
max_row = min(max_row, tile_matrix.matrixheight - 1)
# Clamp to any layer-specific limits on the tile matrix.
if tile_matrix_limits:
min_col = max(min_col, tile_matrix_limits.mintilecol)
max_col = min(max_col, tile_matrix_limits.maxtilecol)
min_row = max(min_row, tile_matrix_limits.mintilerow)
max_row = min(max_row, tile_matrix_limits.maxtilerow)
return min_col, max_col, min_row, max_row
def _wmts_images(self, wmts, layer, matrix_set_name, extent,
max_pixel_span):
"""
Add images from the specified WMTS layer and matrix set to cover
the specified extent at an appropriate resolution.
The zoom level (aka. tile matrix) is chosen to give the lowest
possible resolution which still provides the requested quality.
If insufficient resolution is available, the highest available
resolution is used.
Args:
* wmts - The owslib.wmts.WebMapTileService providing the tiles.
* layer - The owslib.wmts.ContentMetadata (aka. layer) to draw.
* matrix_set_name - The name of the matrix set to use.
* extent - Tuple of (left, right, bottom, top) in Axes coordinates.
* max_pixel_span - Preferred maximum pixel width or height
in Axes coordinates.
"""
# Find which tile matrix has the appropriate resolution.
tile_matrix_set = wmts.tilematrixsets[matrix_set_name]
tile_matrices = tile_matrix_set.tilematrix.values()
meters_per_unit = METERS_PER_UNIT[tile_matrix_set.crs]
tile_matrix = self._choose_matrix(tile_matrices, meters_per_unit,
max_pixel_span)
# Determine which tiles are required to cover the requested extent.
tile_span_x, tile_span_y = self._tile_span(tile_matrix,
meters_per_unit)
tile_matrix_set_links = getattr(layer, 'tilematrixsetlinks', None)
if tile_matrix_set_links is None:
tile_matrix_limits = None
else:
tile_matrix_set_link = tile_matrix_set_links[matrix_set_name]
tile_matrix_limits = tile_matrix_set_link.tilematrixlimits.get(
tile_matrix.identifier)
min_col, max_col, min_row, max_row = self._select_tiles(
tile_matrix, tile_matrix_limits, tile_span_x, tile_span_y, extent)
# Find the relevant section of the image cache.
tile_matrix_id = tile_matrix.identifier
cache_by_wmts = WMTSRasterSource._shared_image_cache
cache_by_layer_matrix = cache_by_wmts.setdefault(wmts, {})
image_cache = cache_by_layer_matrix.setdefault((layer.id,
tile_matrix_id), {})
# To avoid nasty seams between the individual tiles, we
# accumulate the tile images into a single image.
big_img = None
n_rows = 1 + max_row - min_row
n_cols = 1 + max_col - min_col
# Ignore out-of-range errors if the current version of OWSLib
# doesn't provide the regional information.
ignore_out_of_range = tile_matrix_set_links is None
for row in range(min_row, max_row + 1):
for col in range(min_col, max_col + 1):
# Get the tile's Image from the cache if possible.
img_key = (row, col)
img = image_cache.get(img_key)
if img is None:
try:
tile = wmts.gettile(
layer=layer.id,
tilematrixset=matrix_set_name,
tilematrix=tile_matrix_id,
row=row, column=col)
except owslib.util.ServiceException as exception:
if ('TileOutOfRange' in exception.message and
ignore_out_of_range):
continue
raise exception
img = Image.open(io.BytesIO(tile.read()))
image_cache[img_key] = img
if big_img is None:
size = (img.size[0] * n_cols, img.size[1] * n_rows)
big_img = Image.new('RGBA', size, (255, 255, 255, 255))
top = (row - min_row) * tile_matrix.tileheight
left = (col - min_col) * tile_matrix.tilewidth
big_img.paste(img, (left, top))
if big_img is None:
img_extent = None
else:
matrix_min_x, matrix_max_y = tile_matrix.topleftcorner
min_img_x = matrix_min_x + tile_span_x * min_col
max_img_y = matrix_max_y - tile_span_y * min_row
img_extent = (min_img_x, min_img_x + n_cols * tile_span_x,
max_img_y - n_rows * tile_span_y, max_img_y)
return big_img, img_extent
class WFSGeometrySource(object):
"""Web Feature Service (WFS) retrieval for Cartopy."""
def __init__(self, service, features, getfeature_extra_kwargs=None):
"""
Args:
* service:
The URL of a WFS, or an instance of
:class:`owslib.wfs.WebFeatureService`.
* features:
The typename(s) of the features from the WFS that
will be retrieved and made available as geometries.
Kwargs:
* getfeature_extra_kwargs:
Extra keyword args to pass to the service's `getfeature` call.
"""
if WebFeatureService is None:
raise ImportError(_OWSLIB_REQUIRED)
if isinstance(service, six.string_types):
service = WebFeatureService(service)
if isinstance(features, six.string_types):
features = [features]
if getfeature_extra_kwargs is None:
getfeature_extra_kwargs = {}
if not features:
raise ValueError('One or more features must be specified.')
for feature in features:
if feature not in service.contents:
raise ValueError('The {!r} feature does not exist in this '
'service.'.format(feature))
self.service = service
self.features = features
self.getfeature_extra_kwargs = getfeature_extra_kwargs
self._default_urn = None
def default_projection(self):
"""
Return a :class:`cartopy.crs.Projection` in which the WFS
service can supply the requested features.
"""
# Using first element in crsOptions (default).
if self._default_urn is None:
default_urn = set(self.service.contents[feature].crsOptions[0] for
feature in self.features)
if len(default_urn) != 1:
ValueError('Failed to find a single common default SRS '
'across all features (typenames).')
else:
default_urn = default_urn.pop()
default_srs = default_urn.id
if six.text_type(default_urn) not in _URN_TO_CRS:
raise ValueError('Unknown mapping from SRS/CRS_URN {!r} to '
'cartopy projection.'.format(default_urn))
self._default_urn = default_urn
return _URN_TO_CRS[six.text_type(self._default_urn)]
def fetch_geometries(self, projection, extent):
"""
Return any Point, Linestring or LinearRing geometries available
from the WFS that lie within the specified extent.
Args:
* projection: :class:`cartopy.crs.Projection`
The projection in which the extent is specified and in
which the geometries should be returned. Only the default
(native) projection is supported.
* extent: four element tuple
(min_x, max_x, min_y, max_y) tuple defining the geographic extent
of the geometries to obtain.
Returns:
A list of Shapely geometries.
"""
if self.default_projection() != projection:
raise ValueError('Geometries are only available in projection '
'{!r}.'.format(self.default_projection()))
min_x, max_x, min_y, max_y = extent
response = self.service.getfeature(typename=self.features,
bbox=(min_x, min_y, max_x, max_y),
**self.getfeature_extra_kwargs)
geoms_by_srs = self._to_shapely_geoms(response)
if not geoms_by_srs:
geoms = []
elif len(geoms_by_srs) > 1:
raise ValueError('Unexpected response from the WFS server. The '
'geometries are in multiple SRSs, when only one '
'was expected.')
else:
srs, geoms = list(geoms_by_srs.items())[0]
# Attempt to verify the SRS associated with the geometries (if any)
# matches the specified projection.
if srs is not None:
if srs in _URN_TO_CRS:
geom_proj = _URN_TO_CRS[srs]
if geom_proj != projection:
raise ValueError('The geometries are not in expected '
'projection. Expected {!r}, got '
'{!r}.'.format(projection, geom_proj))
else:
msg = 'Unable to verify matching projections due ' \
'to incomplete mappings from SRS identifiers ' \
'to cartopy projections. The geometries have ' \
'an SRS of {!r}.'.format(srs)
warnings.warn(msg)
return geoms
def _to_shapely_geoms(self, response):
"""
Convert polygon coordinate strings in WFS response XML to Shapely
geometries.
Args:
* response: (file-like object)
WFS response XML data.
Returns:
A dictionary containing geometries, with key-value pairs of
the form {srsname: [geoms]}.
"""
linear_rings_data = []
linestrings_data = []
points_data = []
tree = ElementTree.parse(response)
for node in tree.findall('.//{}msGeometry'.format(_MAP_SERVER_NS)):
# Find LinearRing geometries in our msGeometry node.
find_str = './/{gml}LinearRing'.format(gml=_GML_NS)
if self._node_has_child(node, find_str):
data = self._find_polygon_coords(node, find_str)
linear_rings_data.extend(data)
# Find LineString geometries in our msGeometry node.
find_str = './/{gml}LineString'.format(gml=_GML_NS)
if self._node_has_child(node, find_str):
data = self._find_polygon_coords(node, find_str)
linestrings_data.extend(data)
# Find Point geometries in our msGeometry node.
find_str = './/{gml}Point'.format(gml=_GML_NS)
if self._node_has_child(node, find_str):
data = self._find_polygon_coords(node, find_str)
points_data.extend(data)
geoms_by_srs = {}
for srs, x, y in linear_rings_data:
geoms_by_srs.setdefault(srs, []).append(
sgeom.LinearRing(zip(x, y)))
for srs, x, y in linestrings_data:
geoms_by_srs.setdefault(srs, []).append(
sgeom.LineString(zip(x, y)))
for srs, x, y in points_data:
geoms_by_srs.setdefault(srs, []).append(
sgeom.Point(zip(x, y)))
return geoms_by_srs
def _find_polygon_coords(self, node, find_str):
"""
Return the x, y coordinate values for all the geometries in
a given`node`.
Args:
* node: :class:`xml.etree.ElementTree.Element`
Node of the parsed XML response.
* find_str: string
A search string used to match subelements that contain
the coordinates of interest, for example:
'.//{http://www.opengis.net/gml}LineString'
Returns:
A list of (srsName, x_vals, y_vals) tuples.
"""
data = []
for polygon in node.findall(find_str):
feature_srs = polygon.attrib.get('srsName')
x, y = [], []
# We can have nodes called `coordinates` or `coord`.
coordinates_find_str = '{}coordinates'.format(_GML_NS)
coords_find_str = '{}coord'.format(_GML_NS)
if self._node_has_child(polygon, coordinates_find_str):
points = polygon.findtext(coordinates_find_str)
coords = points.strip().split(' ')
for coord in coords:
x_val, y_val = coord.split(',')
x.append(float(x_val))
y.append(float(y_val))
elif self._node_has_child(polygon, coords_find_str):
for coord in polygon.findall(coords_find_str):
x.append(float(coord.findtext('{}X'.format(_GML_NS))))
y.append(float(coord.findtext('{}Y'.format(_GML_NS))))
else:
raise ValueError('Unable to find or parse coordinate values '
'from the XML.')
data.append((feature_srs, x, y))
return data
@staticmethod
def _node_has_child(node, find_str):
"""
Return whether `node` contains (at any sub-level), a node with name
equal to `find_str`.
"""
element = node.find(find_str)
return element is not None
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