Thuban/Model/resource.py

# Copyright (c) 2003 by Intevation GmbH
# Authors:
# Jonathan Coles <[email protected]>
#
# This program is free software under the GPL (>=v2)
# Read the file COPYING coming with Thuban for details.

"""Handle resources loaded from files such as projections"""

__version__ = "$Revision$"
# $Source$
# $Id$


import os
import os.path
import weakref

import Thuban
from Thuban import _

from Thuban.Lib.fileutil import get_application_dir

from Thuban.Model.xmlreader import XMLReader
from Thuban.Model.xmlwriter import XMLWriter
from Thuban.Model.proj import Projection, ProjFile
from xml.sax import SAXParseException

projdir = \
        os.path.join(Thuban.__path__[0], os.pardir, "Resources", "Projections")


PROJ_EXT = ".proj"

has_gdal_support = lambda: False
try:
    # first try to see if our extension module is there. if it 
    # wasn't even compiled, we obviously don't have gdal support.
    import gdalwarp

    # now try to import the python extension. if this doesn't
    # exist then we can't do anything.
    import gdal

    """Return True if the gdal library is available."""
    has_gdal_support = lambda: True
except ImportError:
    pass

projfile_cache = weakref.WeakValueDictionary()

def clear_proj_file_cache():
    """Clear the cache of ProjFile objects maintained by read_proj_file.

    This function is probably only useful for the test suite.
    """
    projfile_cache.clear()

def read_proj_file(filename):
    """Read a .proj file and return a ProjFile object and warnings

    The return value is a tuple with the ProjFile object and a list of
    strings with warnings messages that might have been generated by the
    proj file parser.

    The objects returned cached so that reading the same file
    (identified by its absolute name) several times yields the same
    ProjFile object. The cache uses weak references so the objects will
    be removed from the cache once the last reference an object in the
    cache is removed.

    Raises IOError if the file cannot be opened, OSError if the file
    cannot be read and SAXParseException if the file is not valid XML.
    """
    filename = os.path.abspath(filename)
    if filename in projfile_cache:
        return projfile_cache[filename], []
    else:
        handler = ProjFileReader()
        handler.read(filename)
        proj_file = handler.GetProjFile()
        projfile_cache[filename] = proj_file
        return proj_file, handler.GetWarnings()

def write_proj_file(pf):
    """Write a single .proj file

    Raises IOError if the file cannot be written.
    """

    saver = ProjFileSaver(pf)
    saver.write(pf.GetFilename())


# Constants for the get_system_proj_file function
DEFAULT_PROJ_FILE = "defaults.proj"
EPSG_PROJ_FILE = "epsg.proj"

def get_system_proj_file(filename):
    """Return the projections from the indicated file and a list with warnings

    The filename argument should be the name of a file in the directory
    with Thuban's default projection files (Resources/Projections/). If
    possible callers should not use hardwired string literal for the
    name to avoid unnecessary duplication. Instead they should use one
    of the predefined constants, currently DEFAULT_PROJ_FILE or
    EPSG_PROJ_FILE.

    The return value is a tuple with the projections in a ProjFile
    object and a list of strings with warning messages. The warnings
    list is usually empty but may contain messages about ignored errors.

    If the file could could not be opened return an empty projection
    file object set to store data in the indicated default file.
    """
    fullname = os.path.join(projdir, filename)
    try:
        return read_proj_file(fullname)
    except (OSError, IOError, SAXParseException), val:
        msg = _('Could not read "%s": %s') % (fullname, str(val))
        return ProjFile(fullname), [msg]

def get_user_proj_file():
    """Return the user's projections and a list with warnings

    The projections read from the user's thuban projection file (usually
    in ~/.thuban/user.proj). The return value is a tuple with the
    projections in a ProjFile object and a list of strings with warning
    messages. The warnings list is usually empty but may contain
    messages about ignored errors.

    If the file could could not be opened return an empty projection
    file object set to store data in the default file.
    """
    usrdir  = get_application_dir()
    filename = os.path.join(usrdir, "user.proj")
    try:
        return read_proj_file(filename)
    except (OSError, IOError, SAXParseException), val:
        msg = _('Could not read "%s": %s') % (filename, str(val))
        return ProjFile(filename), [msg]


class ProjFileReader(XMLReader):

    def __init__(self):
        XMLReader.__init__(self)
        self.projfile = ProjFile("")
        self.warnings = []

        XMLReader.AddDispatchers(self,
            {'projection': ("start_projection", "end_projection"),
             'parameter':  ("start_parameter", None)})

    def read(self, file_or_filename):
        XMLReader.read(self, file_or_filename)

        self.projfile.SetFilename(XMLReader.GetFilename(self))

    def start_projection(self, name, qname, attrs):
        self.params = []
        name = self.encode(attrs.get((None, 'name')))
        if name is None:
            name = _("Unknown")
        self.name = name
        self.epsg = self.encode(attrs.get((None, 'epsg')))

    def end_projection(self, name, qname):
        try:
            proj = Projection(self.params, self.name, epsg = self.epsg)
        except IOError, val:
            self.warnings.append(_('Error in projection "%s": %s')
                                 % (self.name, str(val)))
        else:
            self.projfile.Add(proj)

    def start_parameter(self, name, qname, attrs):
        s = attrs.get((None, 'value'))
        s = str(s) # we can't handle unicode in proj
        self.params.append(s)

    def GetProjFile(self):
        return self.projfile

    def GetWarnings(self):
        """Return the list of warning messages that may have been produced"""
        return self.warnings


class ProjFileSaver(XMLWriter):

    def __init__(self, pf):
        XMLWriter.__init__(self)
        self.__pf = pf

    def write(self, file_or_filename):
        XMLWriter.write(self, file_or_filename)

        self.write_header("projectionlist", "projfile.dtd")
        self.write_projfile(self.__pf)
        self.close()

    def write_projfile(self, pf):

        self.open_element("projectionlist")

        for p in pf.GetProjections():
            attrs = {"name": p.GetName()}
            if p.EPSGCode():
                attrs["epsg"] = p.EPSGCode()
            self.open_element("projection", attrs)

            for param in p.GetAllParameters():
                self.write_element("parameter", {"value": param})

            self.close_element("projection")

        self.close_element("projectionlist")


1	# Copyright (c) 2003 by Intevation GmbH
2	# Authors:
3	# Jonathan Coles <[email protected]>
4	#
5	# This program is free software under the GPL (>=v2)
6	# Read the file COPYING coming with Thuban for details.
7
8	"""Handle resources loaded from files such as projections"""
9
10	__version__ = "$Revision$"
11	# $Source$
12	# $Id$
13
14
15	import os
16	import os.path
17	import weakref
18
19	import Thuban
20	from Thuban import _
21
22	from Thuban.Lib.fileutil import get_application_dir
23
24	from Thuban.Model.xmlreader import XMLReader
25	from Thuban.Model.xmlwriter import XMLWriter
26	from Thuban.Model.proj import Projection, ProjFile
27	from xml.sax import SAXParseException
28
29	projdir = \
30	os.path.join(Thuban.__path__[0], os.pardir, "Resources", "Projections")
31
32
33	PROJ_EXT = ".proj"
34
35	has_gdal_support = lambda: False
36	try:
37	# first try to see if our extension module is there. if it
38	# wasn't even compiled, we obviously don't have gdal support.
39	import gdalwarp
40
41	# now try to import the python extension. if this doesn't
42	# exist then we can't do anything.
43	import gdal
44
45	"""Return True if the gdal library is available."""
46	has_gdal_support = lambda: True
47	except ImportError:
48	pass
49
50	projfile_cache = weakref.WeakValueDictionary()
51
52	def clear_proj_file_cache():
53	"""Clear the cache of ProjFile objects maintained by read_proj_file.
54
55	This function is probably only useful for the test suite.
56	"""
57	projfile_cache.clear()
58
59	def read_proj_file(filename):
60	"""Read a .proj file and return a ProjFile object and warnings
61
62	The return value is a tuple with the ProjFile object and a list of
63	strings with warnings messages that might have been generated by the
64	proj file parser.
65
66	The objects returned cached so that reading the same file
67	(identified by its absolute name) several times yields the same
68	ProjFile object. The cache uses weak references so the objects will
69	be removed from the cache once the last reference an object in the
70	cache is removed.
71
72	Raises IOError if the file cannot be opened, OSError if the file
73	cannot be read and SAXParseException if the file is not valid XML.
74	"""
75	filename = os.path.abspath(filename)
76	if filename in projfile_cache:
77	return projfile_cache[filename], []
78	else:
79	handler = ProjFileReader()
80	handler.read(filename)
81	proj_file = handler.GetProjFile()
82	projfile_cache[filename] = proj_file
83	return proj_file, handler.GetWarnings()
84
85	def write_proj_file(pf):
86	"""Write a single .proj file
87
88	Raises IOError if the file cannot be written.
89	"""
90
91	saver = ProjFileSaver(pf)
92	saver.write(pf.GetFilename())
93
94
95	# Constants for the get_system_proj_file function
96	DEFAULT_PROJ_FILE = "defaults.proj"
97	EPSG_PROJ_FILE = "epsg.proj"
98
99	def get_system_proj_file(filename):
100	"""Return the projections from the indicated file and a list with warnings
101
102	The filename argument should be the name of a file in the directory
103	with Thuban's default projection files (Resources/Projections/). If
104	possible callers should not use hardwired string literal for the
105	name to avoid unnecessary duplication. Instead they should use one
106	of the predefined constants, currently DEFAULT_PROJ_FILE or
107	EPSG_PROJ_FILE.
108
109	The return value is a tuple with the projections in a ProjFile
110	object and a list of strings with warning messages. The warnings
111	list is usually empty but may contain messages about ignored errors.
112
113	If the file could could not be opened return an empty projection
114	file object set to store data in the indicated default file.
115	"""
116	fullname = os.path.join(projdir, filename)
117	try:
118	return read_proj_file(fullname)
119	except (OSError, IOError, SAXParseException), val:
120	msg = _('Could not read "%s": %s') % (fullname, str(val))
121	return ProjFile(fullname), [msg]
122
123	def get_user_proj_file():
124	"""Return the user's projections and a list with warnings
125
126	The projections read from the user's thuban projection file (usually
127	in ~/.thuban/user.proj). The return value is a tuple with the
128	projections in a ProjFile object and a list of strings with warning
129	messages. The warnings list is usually empty but may contain
130	messages about ignored errors.
131
132	If the file could could not be opened return an empty projection
133	file object set to store data in the default file.
134	"""
135	usrdir = get_application_dir()
136	filename = os.path.join(usrdir, "user.proj")
137	try:
138	return read_proj_file(filename)
139	except (OSError, IOError, SAXParseException), val:
140	msg = _('Could not read "%s": %s') % (filename, str(val))
141	return ProjFile(filename), [msg]
142
143
144	class ProjFileReader(XMLReader):
145
146	def __init__(self):
147	XMLReader.__init__(self)
148	self.projfile = ProjFile("")
149	self.warnings = []
150
151	XMLReader.AddDispatchers(self,
152	{'projection': ("start_projection", "end_projection"),
153	'parameter': ("start_parameter", None)})
154
155	def read(self, file_or_filename):
156	XMLReader.read(self, file_or_filename)
157
158	self.projfile.SetFilename(XMLReader.GetFilename(self))
159
160	def start_projection(self, name, qname, attrs):
161	self.params = []
162	name = self.encode(attrs.get((None, 'name')))
163	if name is None:
164	name = _("Unknown")
165	self.name = name
166	self.epsg = self.encode(attrs.get((None, 'epsg')))
167
168	def end_projection(self, name, qname):
169	try:
170	proj = Projection(self.params, self.name, epsg = self.epsg)
171	except IOError, val:
172	self.warnings.append(_('Error in projection "%s": %s')
173	% (self.name, str(val)))
174	else:
175	self.projfile.Add(proj)
176
177	def start_parameter(self, name, qname, attrs):
178	s = attrs.get((None, 'value'))
179	s = str(s) # we can't handle unicode in proj
180	self.params.append(s)
181
182	def GetProjFile(self):
183	return self.projfile
184
185	def GetWarnings(self):
186	"""Return the list of warning messages that may have been produced"""
187	return self.warnings
188
189
190	class ProjFileSaver(XMLWriter):
191
192	def __init__(self, pf):
193	XMLWriter.__init__(self)
194	self.__pf = pf
195
196	def write(self, file_or_filename):
197	XMLWriter.write(self, file_or_filename)
198
199	self.write_header("projectionlist", "projfile.dtd")
200	self.write_projfile(self.__pf)
201	self.close()
202
203	def write_projfile(self, pf):
204
205	self.open_element("projectionlist")
206
207	for p in pf.GetProjections():
208	attrs = {"name": p.GetName()}
209	if p.EPSGCode():
210	attrs["epsg"] = p.EPSGCode()
211	self.open_element("projection", attrs)
212
213	for param in p.GetAllParameters():
214	self.write_element("parameter", {"value": param})
215
216	self.close_element("projection")
217
218	self.close_element("projectionlist")
219
220
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