diff --git a/simgear/misc/props.cxx b/simgear/misc/props.cxx
index b5919127..d7de035b 100644
--- a/simgear/misc/props.cxx
+++ b/simgear/misc/props.cxx
@@ -1209,7 +1209,7 @@ SGPropertyNode::getSubNode (const string &subpath) const
 SGValue *
 SGPropertyNode::getValue (const string &subpath)
 {
-  if (_props == 0 || _path.size() == 0)
+  if (_props == 0)
     return 0;
 
   if (subpath.size() == 0)
@@ -1225,7 +1225,7 @@ SGPropertyNode::getValue (const string &subpath)
 bool
 SGPropertyNode::getBoolValue (const string &subpath, bool defaultValue) const
 {
-  if (_props == 0 || _path.size() == 0)
+  if (_props == 0)
     return defaultValue;
 
   if (subpath == "")
@@ -1242,7 +1242,7 @@ SGPropertyNode::getBoolValue (const string &subpath, bool defaultValue) const
 int
 SGPropertyNode::getIntValue (const string &subpath, int defaultValue) const
 {
-  if (_props == 0 || _path.size() == 0)
+  if (_props == 0)
     return defaultValue;
 
   if (subpath == "")
@@ -1259,7 +1259,7 @@ SGPropertyNode::getIntValue (const string &subpath, int defaultValue) const
 float
 SGPropertyNode::getFloatValue (const string &subpath, float defaultValue) const
 {
-  if (_props == 0 || _path.size() == 0)
+  if (_props == 0)
     return defaultValue;
 
   if (subpath == "")
@@ -1277,7 +1277,7 @@ double
 SGPropertyNode::getDoubleValue (const string &subpath,
 				double defaultValue) const
 {
-  if (_props == 0 || _path.size() == 0)
+  if (_props == 0)
     return defaultValue;
 
   if (subpath == "")
@@ -1295,7 +1295,7 @@ const string &
 SGPropertyNode::getStringValue (const string &subpath,
 				const string &defaultValue) const
 {
-  if (_props == 0 || _path.size() == 0)
+  if (_props == 0)
     return defaultValue;
 
   if (subpath == "")
diff --git a/simgear/misc/props.hxx b/simgear/misc/props.hxx
index ebaaf7f2..0f31c24c 100644
--- a/simgear/misc/props.hxx
+++ b/simgear/misc/props.hxx
@@ -406,7 +406,10 @@ private:
 ////////////////////////////////////////////////////////////////////////
 
 extern bool readPropertyList (istream &input, SGPropertyList * props);
+extern bool readPropertyList (const string &file, SGPropertyList * props);
 extern bool writePropertyList (ostream &output, const SGPropertyList * props);
+extern bool writePropertyList (const string &file,
+			       const SGPropertyList * props);
 
 
 
diff --git a/simgear/misc/props_io.cxx b/simgear/misc/props_io.cxx
index 8515fc73..35c282f6 100644
--- a/simgear/misc/props_io.cxx
+++ b/simgear/misc/props_io.cxx
@@ -9,10 +9,12 @@
 #include "props.hxx"
 
 #include <iostream>
+#include <fstream>
 #include <string>
 #include <vector>
 
 using std::istream;
+using std::ifstream;
 using std::ostream;
 using std::string;
 using std::vector;
@@ -221,6 +223,19 @@ readPropertyList (istream &input, SGPropertyList * props)
   return readXML(input, visitor) && visitor.isOK();
 }
 
+bool
+readPropertyList (const string &file, SGPropertyList * props)
+{
+  ifstream input(file.c_str());
+  if (input.good()) {
+    return readPropertyList(input, props);
+  } else {
+    FG_LOG(FG_INPUT, FG_ALERT, "Error reading property list from file "
+	   << file);
+    return false;
+  }
+}
+
 
 
 ////////////////////////////////////////////////////////////////////////
@@ -330,3 +345,16 @@ writePropertyList (ostream &output, const SGPropertyList * props)
 
   output << "</PropertyList>" << endl;
 }
+
+bool
+writePropertyList (const string &file, const SGPropertyList * props)
+{
+  ofstream output(file.c_str());
+  if (output.good()) {
+    return writePropertyList(output, props);
+  } else {
+    FG_LOG(FG_INPUT, FG_ALERT, "Cannot write property list to file "
+	   << file);
+    return false;
+  }
+}
diff --git a/simgear/sky/sphere.cxx b/simgear/sky/sphere.cxx
index 21969e2e..b67f2cc6 100644
--- a/simgear/sky/sphere.cxx
+++ b/simgear/sky/sphere.cxx
@@ -34,6 +34,7 @@
 #include <plib/sg.h>
 #include <plib/ssg.h>
 
+FG_USING_NAMESPACE(std);
 
 // return a sphere object as an ssgBranch
 ssgBranch *ssgMakeSphere( ssgSimpleState *state, ssgColourArray *cl,