There are two ways to retrieve the magnetic north declination at a certain location and time.

  • Either create a TLcdMagneticNorthMeasureProviderFactory instance and use it like any other ILcdModelMeasureProviderFactory implementation: 

    //Use one of the available model decoders to decode the model
//LuciadLightspeed offers the TLcdWMMModelDecoder for WMM models,
//and the TLcdIGRFModelDecoder for IGRF models.
TLcdWMMModelDecoder modelDecoder = new TLcdWMMModelDecoder();

//Specify the date on the model decoder
Calendar calendar = Calendar.getInstance();
calendar.set(2020, Calendar.AUGUST, 26, 16, 52);
modelDecoder.setDate(calendar);

//Decode the model
ILcdModel model = modelDecoder.decode("Data/magneticnorth/WMM2020.COF");

//Create an ALcdMeasureProvider for the magnetic north model,
//using the TLcdMagneticNorthMeasureProviderFactory
TLcdMagneticNorthMeasureProviderFactory modelMeasureProviderFactory = new TLcdMagneticNorthMeasureProviderFactory();
ALcdMeasureProvider measureProvider = modelMeasureProviderFactory.createMeasureProvider(model);

//Query the measure provider for the measurements at a specific location
TLcdISO19103Measure[] declinations =
    measureProvider.retrieveMeasuresAt(new TLcdLonLatPoint(10, 10),
                                       new TLcdGeodeticReference(),
                                       ALcdMeasureProvider.Parameters.newBuilder().build());
TLcdISO19103Measure declination = declinations[0];

  • Or, query the ILcdMagneticNorthMap directly: 

    //Decode the magnetic map.
//In this example, we use a WMM magnetic map.
//LuciadLightspeed also supports IGRF maps (see the TLcdIGRFMagneticNorthMap class)
TLcdWMMMagneticNorthMap map = new TLcdWMMMagneticNorthMap("Data/magneticnorth/WMM2020.COF");

//Set the date you are interested in on the map
Calendar calendar = Calendar.getInstance();
calendar.set(2020, Calendar.AUGUST, 26, 16, 52);
map.setDate(calendar);

//Retrieve the declination for the location of interest.
//The location is a WGS-84 point
float declinationValue = map.retrieveDeclinationAt(new TLcdLonLatPoint(10, 10));

//The returned declination value is expressed in degrees
TLcdISO19103Measure declination = new TLcdISO19103Measure(declinationValue, TLcdAngleUnit.DEGREE);