# (C) British Crown Copyright 2014, Met Office
#
# 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 <http://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
import io
import math
import weakref
from owslib.wms import WebMapService
import PIL.Image
import owslib.util
import owslib.wmts
from cartopy.io import RasterSource
import cartopy.crs as ccrs
# Hardcode some known EPSG codes for now.
_CRS_TO_OGC_SRS = {ccrs.PlateCarree(): 'EPSG:4326'
}
# 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::900913': 1,
'urn:ogc:def:crs:OGC:1.3:CRS84': _WGS84_METERS_PER_UNIT,
}
_URN_TO_CRS = {
'urn:ogc:def:crs:EPSG::900913': ccrs.GOOGLE_MERCATOR,
'urn:ogc:def:crs:OGC:1.3:CRS84': ccrs.PlateCarree(),
}
[docs]class WMSRasterSource(RasterSource):
"""
A WMS imagery retriever which can be added to a map.
.. note:: Requires owslib and PIL 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 isinstance(service, basestring):
service = WebMapService(service)
if isinstance(layers, basestring):
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
self._srs_for_projection_id = {}
def _srs(self, projection):
key = id(projection)
srs = self._srs_for_projection_id.get(key)
if srs is None:
srs = _CRS_TO_OGC_SRS.get(projection)
if srs is None:
raise ValueError('The projection {!r} was not convertible to '
'a suitable WMS SRS.'.format(projection))
for layer in self.layers:
if srs not in self.service.contents[layer].crsOptions:
raise ValueError('The SRS {} is not a valid SRS for the '
'{!r} WMS layer.'.format(srs, layer))
self._srs_for_projection_id[key] = srs
return srs
def validate_projection(self, projection):
self._srs(projection)
def fetch_raster(self, projection, extent, target_resolution):
service = self.service
min_x, max_x, min_y, max_y = extent
wms_image = service.getmap(layers=self.layers,
srs=self._srs(projection),
bbox=(min_x, min_y, max_x, max_y),
size=target_resolution, format='image/png',
**self.getmap_extra_kwargs)
wms_image = PIL.Image.open(io.BytesIO(wms_image.read()))
return wms_image, extent
[docs]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 PIL 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 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 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
ok_tile_matrices = filter(lambda tm: tm.scaledenominator <= max_scale,
tile_matrices)
if ok_tile_matrices:
tile_matrix = ok_tile_matrices[0]
else:
tile_matrix = tile_matrices[-1]
return tile_matrix
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 = PIL.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 = PIL.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
