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	jonathan	696	# 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	bh	1542	"""Handle resources loaded from files such as projections"""
9
10			__version__ = "$Revision$"
11			# $Source$
12			# $Id$
13
14
15	jonathan	696	import os
16	frank	1132	import os.path
17	bh	1830	import weakref
18	frank	1132
19	jonathan	696	import Thuban
20	jonathan	875	from Thuban import _
21
22	frank	1149	from Thuban.Lib.fileutil import get_application_dir
23
24	jonathan	1161	from Thuban.Model.xmlreader import XMLReader
25			from Thuban.Model.xmlwriter import XMLWriter
26	jonathan	696	from Thuban.Model.proj import Projection, ProjFile
27	jonathan	727	from xml.sax import SAXParseException
28	jonathan	696
29			projdir = \
30			os.path.join(Thuban.__path__[0], os.pardir, "Resources", "Projections")
31
32
33			PROJ_EXT = ".proj"
34
35	jonathan	1161	has_gdal_support = lambda: False
36			try:
37	jonathan	1230	# 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	jonathan	1161	import gdal
44	jonathan	1230
45	jonathan	1161	"""Return True if the gdal library is available."""
46			has_gdal_support = lambda: True
47			except ImportError:
48			pass
49
50	bh	1830	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	jonathan	1161	def read_proj_file(filename):
60	bh	1786	"""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	bh	1830	proj file parser.
65	bh	1786
66	bh	1830	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	bh	1786	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	jonathan	718	"""
75	bh	1830	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	jonathan	696
85	jonathan	1161	def write_proj_file(pf):
86	jonathan	727	"""Write a single .proj file
87
88			Raises IOError if the file cannot be written.
89			"""
90
91	jonathan	696	saver = ProjFileSaver(pf)
92	jonathan	739	saver.write(pf.GetFilename())
93	jonathan	696
94
95	bh	1933	# Constants for the get_system_proj_file function
96			DEFAULT_PROJ_FILE = "defaults.proj"
97			EPSG_PROJ_FILE = "epsg.proj"
98	jonathan	696
99	bh	1933	def get_system_proj_file(filename):
100			"""Return the projections from the indicated file and a list with warnings
101	jonathan	696
102	bh	1933	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	bh	1786	If the file could could not be opened return an empty projection
114	bh	1933	file object set to store data in the indicated default file.
115	jonathan	696	"""
116	bh	1933	fullname = os.path.join(projdir, filename)
117	jonathan	727	try:
118	bh	1933	return read_proj_file(fullname)
119	bh	1786	except (OSError, IOError, SAXParseException), val:
120	bh	1933	msg = _('Could not read "%s": %s') % (fullname, str(val))
121			return ProjFile(fullname), [msg]
122	jonathan	696
123	bh	1786	def get_user_proj_file():
124			"""Return the user's projections and a list with warnings
125	jonathan	696
126	bh	1786	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	jonathan	727	"""
135	jonathan	1189	usrdir = get_application_dir()
136	jonathan	727	filename = os.path.join(usrdir, "user.proj")
137			try:
138	bh	1786	return read_proj_file(filename)
139	jan	1791	except (OSError, IOError, SAXParseException), val:
140	bh	1786	msg = _('Could not read "%s": %s') % (filename, str(val))
141			return ProjFile(filename), [msg]
142	jonathan	727
143	bh	1786
144	jonathan	709	class ProjFileReader(XMLReader):
145	jonathan	696
146	jonathan	709	def __init__(self):
147			XMLReader.__init__(self)
148	bh	1786	self.projfile = ProjFile("")
149			self.warnings = []
150	jonathan	709
151			XMLReader.AddDispatchers(self,
152			{'projection': ("start_projection", "end_projection"),
153			'parameter': ("start_parameter", None)})
154	bh	1786
155	jonathan	709	def read(self, file_or_filename):
156			XMLReader.read(self, file_or_filename)
157
158	bh	1786	self.projfile.SetFilename(XMLReader.GetFilename(self))
159
160	jonathan	696	def start_projection(self, name, qname, attrs):
161			self.params = []
162	bh	1786	name = self.encode(attrs.get((None, 'name')))
163			if name is None:
164			name = _("Unknown")
165			self.name = name
166	bh	1816	self.epsg = self.encode(attrs.get((None, 'epsg')))
167	jonathan	696
168			def end_projection(self, name, qname):
169	bh	1786	try:
170	bh	1816	proj = Projection(self.params, self.name, epsg = self.epsg)
171	bh	1786	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	jonathan	696
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	bh	1786	return self.projfile
184	jonathan	696
185	bh	1786	def GetWarnings(self):
186			"""Return the list of warning messages that may have been produced"""
187			return self.warnings
188
189
190	jonathan	709	class ProjFileSaver(XMLWriter):
191	jonathan	696
192			def __init__(self, pf):
193	jonathan	709	XMLWriter.__init__(self)
194			self.__pf = pf
195	jonathan	696
196			def write(self, file_or_filename):
197	jonathan	709	XMLWriter.write(self, file_or_filename)
198	jonathan	696
199	bh	1755	self.write_header("projectionlist", "projfile.dtd")
200	jonathan	709	self.write_projfile(self.__pf)
201	jonathan	696	self.close()
202
203			def write_projfile(self, pf):
204
205			self.open_element("projectionlist")
206
207			for p in pf.GetProjections():
208	bh	1816	attrs = {"name": p.GetName()}
209			if p.EPSGCode():
210			attrs["epsg"] = p.EPSGCode()
211			self.open_element("projection", attrs)
212	jonathan	696
213	jonathan	709	for param in p.GetAllParameters():
214	jonathan	696	self.write_element("parameter", {"value": param})
215
216			self.close_element("projection")
217
218			self.close_element("projectionlist")
219
220
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svn:keywords	Author Date Id Revision