code: public double getDipAngle( double dlat, double dlong, double year, double altitude )
      {
              calcGeoMag( dlat, dlong, year, altitude );
              return  dip;
      }
docs: Returns the magnetic field dip angle from the
  Department of Defense geomagnetic model and data,
  in degrees.
  
  @param	dlat			Latitude in decimal degrees.
  @param 	dlong		Longitude in decimal degrees.
  @param	year			Date of the calculation in decimal years.
  @param	altitude		Altitude of the calculation in kilometers.
  
  @return  The magnetic field dip angle, in degrees.