Lazy caching of magvar on waypoints. Not used yet, but soon.

src/Navaids/route.cxx

@@ -36,8 +36,11 @@
 #include <simgear/structure/exception.hxx>
 #include <simgear/xml/easyxml.hxx>
 #include <simgear/misc/sg_path.hxx>
+#include <simgear/magvar/magvar.hxx>
+#include <simgear/timing/sg_time.hxx>
 
 // FlightGear
+#include <Main/globals.hxx>
 #include <Navaids/procedure.hxx>
 #include <Navaids/waypoint.hxx>
 #include <Airports/simple.hxx>
@@ -49,13 +52,16 @@ using std::fstream;
 
 namespace flightgear {
 
+const double NO_MAG_VAR = -1000.0; // an impossible mag-var value
+
 Waypt::Waypt(Route* aOwner) :
   _altitudeFt(0.0),
   _speed(0.0),
   _altRestrict(RESTRICT_NONE),
   _speedRestrict(RESTRICT_NONE),
   _owner(aOwner),
-  _flags(0)
+  _flags(0),
+  _magVarDeg(NO_MAG_VAR)
 {
 }
 
@@ -127,6 +133,19 @@ Waypt::courseAndDistanceFrom(const SGGeod& aPos) const
   SGGeodesy::inverse(aPos, position(), course, az2, distance);
   return std::make_pair(course, distance);
 }
+
+double Waypt::magvarDeg() const
+{
+  if (_magVarDeg == NO_MAG_VAR) {
+    // derived classes with a default pos must override this method
+    assert(!(position() == SGGeod()));
+    
+    double jd = globals->get_time_params()->getJD();
+    _magVarDeg = sgGetMagVar(position(), jd);
+  }
+  
+  return _magVarDeg;
+}
   
 ///////////////////////////////////////////////////////////////////////////
 // persistence

src/Navaids/route.hxx

@@ -156,6 +156,12 @@ public:
   bool matches(const SGGeod& aPos) const;
   
   virtual std::string type() const = 0;
+  
+  /**
+   * Magentic variation at/in the vicinity of the waypoint.
+   * For some waypoint types this will always return 0.
+   */
+  virtual double magvarDeg() const;
 protected:
   friend class NavdataVisitor;
   
@@ -187,7 +193,7 @@ private:
 
 	Route* _owner;
 	unsigned short _flags;
-	
+  mutable double _magVarDeg; 
 };
 
 typedef std::vector<WayptRef> WayptVec;

src/Navaids/waypoint.hxx

@@ -206,6 +206,9 @@ public:
   double headingDegMagnetic() const
     { return _magHeading; }
   
+  virtual double magvarDeg() const
+    { return 0.0; }
+  
 private:
   std::string _ident;
   double _magHeading;