joey: thuban/Extensions/wms parser.py,NONE,1.1
cvs@intevation.de
cvs at intevation.de
Wed Mar 24 20:31:56 CET 2004
Author: joey
Update of /thubanrepository/thuban/Extensions/wms
In directory doto:/tmp/cvs-serv13727
Added Files:
parser.py
Log Message:
Finally added the XML parser for the GetCapabilities response.
--- NEW FILE: parser.py ---
# Copyright (c) 2004 by Intevation GmbH
# Authors:
# Martin Schulze <joey at infodrom.org>
#
# This program is free software; you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation; either version 2 of the License, or
# (at your option) any later version.
#
# This program 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 General Public License for more details.
#
# You should have received a copy of the GNU General Public License
# along with this program; if not, write to the Free Software
# Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
"""
Inspect WMS Capabilities for later processing.
Information should only be retrieved with the proper get*() methods.
class WMSCapabilitiesParser:
__init__()
grok(string)
getTitle()
getAbstract()
getFees()
getAccessConstraints()
getFormats()
getLayers()
getSRS()
getLayerTitle(layer)
getLayerSRS(layer)
getLayerLatLonBBox(layer)
getLayerBBox(layer, srs)
isQueryable(layer)
get_srs_discrepancies()
"""
__version__ = "$Revision: 1.1 $"
# $Source: /thubanrepository/thuban/Extensions/wms/parser.py,v $
# $Id: parser.py,v 1.1 2004/03/24 19:31:54 joey Exp $
import xml.dom.minidom
from domutils import getElementsByName, getElementByName
class WMSCapabilitiesParser:
"""
Thuban class to parse capabilities supplied as large string.
This class provides methods to parse and retrieve particular
information from the WMS capabilities XML. Information should
only be extracted by the respective get*() methods.
"""
layers = None
title = None
abstract = None
fees = None
access = None
formats = None
srs_discrepancies = None
def __init__(self):
"""
Initialises an instance in this class.
"""
# Note that we must not initialise internal variables of the
# class in a mutable way or it will be shared among all
# instances. None is immutable, [] is not.
layers = []
def grok(self, data):
"""
Parses the XML response to a WMS GetCapabilities request.
Internal datastructure of the class will be filled.
Information should only be retrieved with the respective
get*() methods.
"""
root = xml.dom.minidom.parseString(data).documentElement
# Extract the title
foo = getElementByName(getElementByName(root, 'Service'), 'Title')
if foo:
self.title = foo.childNodes[0].data
# Extract the abstract
foo = getElementByName(getElementByName(root, 'Service'), 'Abstract')
if foo and len(foo.childNodes[0].data):
self.abstract = foo.childNodes[0].data
# Extract fees information
foo = getElementByName(getElementByName(root, 'Service'), 'Fees')
if foo and len(foo.childNodes[0].data) \
and lower(foo.childNodes[0].data) != 'none':
self.fees = foo.childNodes[0].data
# Extract access information
foo = getElementByName(getElementByName(root, 'Service'),
'AccessConstraints')
if foo and len(foo.childNodes[0].data) \
and lower(foo.childNodes[0].data) != 'none':
self.access = foo.childNodes[0].data
# Extract output format information
foo = getElementsByName(
getElementByName(getElementByName(getElementByName(
root, 'Capability'), 'Request'), 'GetMap'), 'Format')
self.formats = map((lambda i: i.childNodes[0].data), foo)
# Extract layer names
self.layers = []
self.peekLayers(getElementByName(getElementByName(
root, 'Capability'), 'Layer'), -1)
def peekLayers(self, top, parent):
"""
Inspect the provided DOM fragment referenced as top.
This method will inspect all included layers and traverse the
tree recursively in order to fill the internal datastructure.
Note that SRS other than EPSG:* are not yet supported,
especially there is no support for AUTO and NONE.
"""
index = len (self.layers)
self.layers.append({})
self.layers[index]['parent'] = parent
for foo in top.attributes.keys():
if foo == 'queryable':
self.layers[index]['queryable'] \
= int(top.attributes.get(foo).nodeValue)
foo = getElementByName(top, 'Title')
if foo and len(foo.childNodes[0].data):
self.layers[index]['title'] = foo.childNodes[0].data
foo = getElementByName(top, 'Name')
if foo and len(foo.childNodes[0].data):
self.layers[index]['name'] = foo.childNodes[0].data
# These values are only used for an integrity check
for foo in getElementsByName(top, 'SRS'):
for srs in foo.childNodes[0].data.split(" "):
if srs[0:5] == 'EPSG:':
srs = srs[5:]
try:
self.layers[index]['srs'].append(srs)
except KeyError:
self.layers[index]['srs'] = [srs]
foo = getElementByName(top, 'LatLonBoundingBox')
if foo is not None:
self.layers[index]['llbbox'] = {}
for corner in ['minx', 'miny', 'maxx', 'maxy']:
self.layers[index]['llbbox'][corner] \
= foo.attributes.get(corner).nodeValue
boxes = getElementsByName(top, 'BoundingBox')
if boxes != []:
self.layers[index]['bbox'] = {}
for foo in boxes:
srs = foo.attributes.get('SRS').nodeValue
if srs[0:5] == 'EPSG:':
srs = srs[5:]
self.layers[index]['bbox'][srs] = {}
for corner in ['minx', 'miny', 'maxx', 'maxy']:
self.layers[index]['bbox'][srs][corner] \
= foo.attributes.get(corner).nodeValue
# Check for integrity
self.checkLayerSRS(index)
# Traverse subsidiary layers
sublayer = getElementsByName(top, 'Layer')
for l in sublayer:
self.peekLayers(l, index)
def checkLayerSRS(self, index):
"""
Checks the integrity of the underlying XML data.
This is done by comparing the <SRS> elements with the
calculated list from the BoundingBox elements.
index -- position in the layers array to check
"""
pivot = index
calculated = []
while pivot != -1:
if 'bbox' in self.layers[pivot]:
for srs in self.layers[pivot]['bbox'].keys():
if srs not in calculated:
calculated.append(srs)
pivot = self.layers[pivot]['parent']
pivot = index
specified = []
while pivot != -1:
if 'srs' in self.layers[pivot]:
for srs in self.layers[pivot]['srs']:
if srs not in specified:
specified.append(srs)
pivot = self.layers[pivot]['parent']
equal = True
# Check for same number of elements
if len(calculated) != len(specified):
equal = False
# Loop through all elements for existance
for elm in calculated:
if elm not in specified:
equal = False
if not equal:
if self.srs_discrepancies is None:
self.srs_discrepancies = []
if 'name' in self.layers[index]:
id = "name:%s" % self.layers[index]['name']
else:
id = "title:%s" % self.layers[index]['title']
self.srs_discrepancies.append(id)
def getTitle(self):
"""
Returns the main title of the WMS object.
If no title is provided in the capabilities, an empty string
is returned.
"""
if self.title is None:
return ''
else:
return self.title
def getAbstract(self):
"""
Returns the abstract of the WMS object.
If no abstract is provided in the capabilities, an empty
string is returned.
"""
if self.abstract is None:
return ''
else:
return self.abstract
def getFees(self):
"""
Returns the fees information of the WMS object.
If no information is provided in the capabilities or if it is
set to 'none', an empty string is returned.
"""
if self.fees is None:
return ''
else:
return self.fees
def getAccessConstraints(self):
"""
Returns information about access constraints for the WMS object.
If no information is provided in the capabilities or if it is
set to 'none', an empty string is returned.
"""
if self.access is None:
return ''
else:
return self.access
def getFormats(self):
"""
Returns a list of supported output formats.
These are used in the GetMap request. This method will
default to 'image/jpeg' if no format is recognised in XML
Capabilities, assuming that JPEG will always be supported on
the server side.
"""
if self.formats is None:
return ['image/jpeg']
else:
return self.formats
def getLayers(self):
"""
Returns a list of layer names.
Only named layers will be returned, since a layer may have a
title but doesn't have to have a name associated to it as
well. If no layers were found, an empty list is returned.
"""
result = []
for layer in self.layers:
if 'name' in layer:
result.append(layer['name'])
return result
def getSRS(self):
"""
Returns the root list of spatial reference systems (SRS).
This list is taken from the root layer. Those SRS are common
to all subsidiary layers. If no SRS are common to all layers,
an empty list is returned. If no layers were detected, an
empty list is returned as well.
"""
if len(self.layers) == 0:
return []
# index 0 denotes the root layer by design
if 'srs' in self.layers[0].keys():
return self.layers[0]['srs']
def getLayerTitle(self, name):
"""
Returns the title of the named layer.
If no such title or no such layer exists, an empty string is
returned.
"""
for layer in self.layers:
if 'name' in layer:
if layer['name'] == name:
if 'title' in layer:
return layer['title']
return ''
def getLayerSRS(self, name):
"""
Returns a list of spacial reference systems (SRS).
The SRS are specified by the European Petroleum Survey Group
(EPSG). There should be at least one SRS per layer, though.
The prefix 'EPSG:' will be stripped. If none exists, an empty
list is returned.
The specification [OGC 01-068r3] says about inheritance of
SRS:
- Every layer is available in one or more SRS (or in an
undefined SRS)
- Geographic information whose SRS is undefined
(e.g. digitised historical maps) shall use 'NONE'
(case-sensitive). This implementation does not support
this.
- Every layer shall have at least one SRS element that is
either stated explicitly or inherited from a parent layer.
- The root layer element shall include a sequence of zero or
more SRS elements listing all SRS which are common for to
all subsidiary layers.
- Layers may optionally add to the global SRS list, or to the
list inherited from a parent layer.
This implementation returns the list of SRS for the given
layer, calculated by looking at BoundingBoxes defined in the
named layer and all layers higher in the hierarchy up to the
root layer which weren't overwritten.
"""
for i in range(len(self.layers)):
if 'name' in self.layers[i]:
if self.layers[i]['name'] == name:
pivot = i
break
else:
return []
result = []
while pivot != -1:
if 'bbox' in self.layers[pivot]:
for srs in self.layers[pivot]['bbox'].keys():
if srs not in result:
result.append(srs)
pivot = self.layers[pivot]['parent']
return result
def getLayerLatLonBBox(self, name):
"""
Returns a dictionary of the LatLonBoundingBox.
... for the named layer if it exists. The SRS is always
EPSG:4326 per convention. There should be at least one,
though, inherited from the root layer at least. If none
exists, the value None is returned.
"""
for layer in self.layers:
if 'name' in layer:
if layer['name'] == name:
if 'llbbox' in layer:
return layer['llbbox']
else:
# No LatLonBoundingBox found in current layer,
# so traverse the hierarchy upwards and check
# again until there is one.
pivot = layer
while pivot['parent'] != -1:
pivot = self.layers[pivot['parent']]
if 'llbbox' in pivot:
return pivot['llbbox']
return None
def getLayerBBox(self, name, srs):
"""
Returns a dictionary of the BoundingBox.
If no such BoundingBox exists, None is returned.
The specification [OGC 01-068r3] says about BoundingBoxes:
- Layers may have zero or more BoundingBox elements what are
either stated explicitly or inherited from a parent layer.
- A layer may have multiple BoundingBox elements, but each one
shall state a different SRS.
- A layer inherits any BoundingBoxes defined by its
parents.
- A BoundingBox inherited from the parent layer for a
particular SRS is replaced by any declaration for the same
SRS in the current layer.
- A BoundingBox in the child layer for a new SRS which is not
already declared by the parent, is added to the list of
BoundingBoxes for the child layer.
- A single layer shall not contain more than one BoundingBox
element for the same SRS.
"""
for layer in self.layers:
if 'name' in layer:
if layer['name'] == name:
if 'bbox' in layer:
if srs in layer['bbox']:
return layer['bbox'][srs]
# No BoundingBox for the given SRS found in
# current layer, so traverse the hierarchy upwards
# and check again until there is one.
pivot = layer
while pivot['parent'] != -1:
pivot = self.layers[pivot['parent']]
if 'bbox' in pivot:
if srs in pivot['bbox']:
return pivot['bbox'][srs]
return None
def isQueryable(self, name):
"""
Returns the value of the queryable attribute of a layer.
This attribute denotes whether this layer can be queried
through the GetFeatureInfo request. The default value is 0.
The specification [OGC 01-068r3] this attribute can be
inherited.
"""
for layer in self.layers:
if 'name' in layer:
if layer['name'] == name:
try:
return layer['queryable']
except KeyError:
# No attribute in this layer, so traverse the
# hierarchy upwards
pivot = layer
while pivot['parent'] != -1:
pivot = self.layers[pivot['parent']]
if 'queryable' in pivot:
return pivot['queryable']
return 0
def get_srs_discrepancies(self):
"""
Returns a list of layer identifications where the denoted SRS
values differ from the calculated ones through BoundingBox
elements.
"""
return self.srs_discrepancies
if __name__ == "__main__":
print "This module cannot be executed standalone."
import os
try:
f = open("test/sample.xml", "r")
except IOError:
try:
f = open(os.path.dirname(__file__) + "/test/sample.xml", "r")
except IOError:
print "Cannot open sample.xml for reading"
if f is not None:
sample = f.read();
f.close()
ina = WMSCapabilitiesParser()
ina.grok(sample)
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