public static DecimalType CalculateDistance(DecimalType latitude1, DecimalType longitude1, DecimalType latitude2,
                                             DecimalType longitude2)
 {
     if (latitude1.IsValid && longitude1.IsValid && latitude2.IsValid && longitude2.IsValid)
     {
         return
             (new DecimalType(
                  CalculateDistance(DecimalType.ToDouble(latitude1), DecimalType.ToDouble(longitude1),
                                    DecimalType.ToDouble(latitude2), DecimalType.ToDouble(longitude2))));
     }
     else
     {
         return(-1);
     }
 }