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    * CS licenses this file to You under the Apache License, Version 2.0
    * (the "License"); you may not use this file except in compliance with
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    *   http://www.apache.org/licenses/LICENSE-2.0
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  package org.orekit.models.earth.troposphere;
  
  import org.hipparchus.Field;
  import org.hipparchus.CalculusFieldElement;
  import org.hipparchus.analysis.UnivariateFunction;
  import org.hipparchus.analysis.interpolation.LinearInterpolator;
  import org.hipparchus.util.FastMath;
  import org.hipparchus.util.MathArrays;
  import org.orekit.annotation.DefaultDataContext;
  import org.orekit.bodies.FieldGeodeticPoint;
  import org.orekit.bodies.GeodeticPoint;
  import org.orekit.data.DataContext;
  import org.orekit.models.earth.weather.FieldPressureTemperatureHumidity;
  import org.orekit.models.earth.weather.PressureTemperatureHumidity;
  import org.orekit.time.AbsoluteDate;
  import org.orekit.time.DateTimeComponents;
  import org.orekit.time.FieldAbsoluteDate;
  import org.orekit.time.TimeScale;
  import org.orekit.utils.FieldTrackingCoordinates;
  import org.orekit.utils.TrackingCoordinates;
  
  /** The Niell Mapping Function  model for radio wavelengths.
   *  This model is an empirical mapping function. It only needs the
   *  values of the station latitude, height and the date for the computations.
   *  <p>
   *  With this model, the hydrostatic mapping function is time and latitude dependent
   *  whereas the wet mapping function is only latitude dependent.
   *  </p>
   *
   * @see "A. E. Niell(1996), Global mapping functions for the atmosphere delay of radio wavelengths,
   *      J. Geophys. Res., 101(B2), pp.  3227–3246, doi:  10.1029/95JB03048."
   *
   * @author Bryan Cazabonne
   *
   */
  @SuppressWarnings("deprecation")
  public class NiellMappingFunctionModel implements MappingFunction, TroposphereMappingFunction {
  
      /** Values for the ah average function. */
      private static final double[] VALUES_FOR_AH_AVERAGE = {
          1.2769934e-3, 1.2683230e-3, 1.2465397e-3, 1.2196049e-3, 1.2045996e-3
      };
  
      /** Values for the bh average function. */
      private static final double[] VALUES_FOR_BH_AVERAGE = {
          2.9153695e-3, 2.9152299e-3, 2.9288445e-3, 2.9022565e-3, 2.9024912e-3
      };
  
      /** Values for the ch average function. */
      private static final double[] VALUES_FOR_CH_AVERAGE = {
          62.610505e-3, 62.837393e-3, 63.721774e-3, 63.824265e-3, 64.258455e-3
      };
  
      /** Values for the ah amplitude function. */
      private static final double[] VALUES_FOR_AH_AMPLITUDE = {
          0.0, 1.2709626e-5, 2.6523662e-5, 3.4000452e-5, 4.1202191e-5
      };
  
      /** Values for the bh amplitude function. */
      private static final double[] VALUES_FOR_BH_AMPLITUDE = {
          0.0, 2.1414979e-5, 3.0160779e-5, 7.2562722e-5, 11.723375e-5
      };
  
      /** X values for the ch amplitude function. */
      private static final double[] VALUES_FOR_CH_AMPLITUDE = {
          0.0, 9.0128400e-5, 4.3497037e-5, 84.795348e-5, 170.37206e-5
      };
  
      /** Values for the aw function. */
      private static final double[] VALUES_FOR_AW = {
          5.8021897e-4, 5.6794847e-4, 5.8118019e-4, 5.9727542e-4, 6.1641693e-4
      };
  
      /** Values for the bw function. */
      private static final double[] VALUES_FOR_BW = {
          1.4275268e-3, 1.5138625e-3, 1.4572752e-3, 1.5007428e-3, 1.7599082e-3
      };
  
      /** Values for the cw function. */
      private static final double[] VALUES_FOR_CW = {
          4.3472961e-2, 4.6729510e-2, 4.3908931e-2, 4.4626982e-2, 5.4736038e-2
      };
  
     /** Values for the cw function. */
     private static final double[] LATITUDE_VALUES = {
         FastMath.toRadians(15.0), FastMath.toRadians(30.0), FastMath.toRadians(45.0), FastMath.toRadians(60.0), FastMath.toRadians(75.0),
     };
 
     /** Interpolation function for the ah (average) term. */
     private final UnivariateFunction ahAverageFunction;
 
     /** Interpolation function for the bh (average) term. */
     private final UnivariateFunction bhAverageFunction;
 
     /** Interpolation function for the ch (average) term. */
     private final UnivariateFunction chAverageFunction;
 
     /** Interpolation function for the ah (amplitude) term. */
     private final UnivariateFunction ahAmplitudeFunction;
 
     /** Interpolation function for the bh (amplitude) term. */
     private final UnivariateFunction bhAmplitudeFunction;
 
     /** Interpolation function for the ch (amplitude) term. */
     private final UnivariateFunction chAmplitudeFunction;
 
     /** Interpolation function for the aw term. */
     private final UnivariateFunction awFunction;
 
     /** Interpolation function for the bw term. */
     private final UnivariateFunction bwFunction;
 
     /** Interpolation function for the cw term. */
     private final UnivariateFunction cwFunction;
 
     /** UTC time scale. */
     private final TimeScale utc;
 
     /** Builds a new instance.
      *
      * <p>This constructor uses the {@link DataContext#getDefault() default data context}.
      *
      * @see #NiellMappingFunctionModel(TimeScale)
      */
     @DefaultDataContext
     public NiellMappingFunctionModel() {
         this(DataContext.getDefault().getTimeScales().getUTC());
     }
 
     /** Builds a new instance.
      * @param utc UTC time scale.
      * @since 10.1
      */
     public NiellMappingFunctionModel(final TimeScale utc) {
         this.utc = utc;
         // Interpolation functions for hydrostatic coefficients
         this.ahAverageFunction    = new LinearInterpolator().interpolate(LATITUDE_VALUES, VALUES_FOR_AH_AVERAGE);
         this.bhAverageFunction    = new LinearInterpolator().interpolate(LATITUDE_VALUES, VALUES_FOR_BH_AVERAGE);
         this.chAverageFunction    = new LinearInterpolator().interpolate(LATITUDE_VALUES, VALUES_FOR_CH_AVERAGE);
         this.ahAmplitudeFunction  = new LinearInterpolator().interpolate(LATITUDE_VALUES, VALUES_FOR_AH_AMPLITUDE);
         this.bhAmplitudeFunction  = new LinearInterpolator().interpolate(LATITUDE_VALUES, VALUES_FOR_BH_AMPLITUDE);
         this.chAmplitudeFunction  = new LinearInterpolator().interpolate(LATITUDE_VALUES, VALUES_FOR_CH_AMPLITUDE);
 
         // Interpolation functions for wet coefficients
         this.awFunction  = new LinearInterpolator().interpolate(LATITUDE_VALUES, VALUES_FOR_AW);
         this.bwFunction  = new LinearInterpolator().interpolate(LATITUDE_VALUES, VALUES_FOR_BW);
         this.cwFunction  = new LinearInterpolator().interpolate(LATITUDE_VALUES, VALUES_FOR_CW);
     }
 
     /** {@inheritDoc} */
     @Override
     @Deprecated
     public double[] mappingFactors(final double elevation, final GeodeticPoint point,
                                    final AbsoluteDate date) {
         return mappingFactors(new TrackingCoordinates(0.0, elevation, 0.0),
                               point,
                               TroposphericModelUtils.STANDARD_ATMOSPHERE,
                               date);
     }
 
     /** {@inheritDoc} */
     @Override
     public double[] mappingFactors(final TrackingCoordinates trackingCoordinates, final GeodeticPoint point,
                                    final PressureTemperatureHumidity weather,
                                    final AbsoluteDate date) {
         // Day of year computation
         final DateTimeComponents dtc = date.getComponents(utc);
         final int dofyear = dtc.getDate().getDayOfYear();
 
         // Temporal factor
         double t0 = 28;
         if (point.getLatitude() < 0) {
             // southern hemisphere: t0 = 28 + an integer half of year
             t0 += 183;
         }
         final double coef    = 2 * FastMath.PI * ((dofyear - t0) / 365.25);
         final double cosCoef = FastMath.cos(coef);
 
         // Compute ah, bh and ch Eq. 5
         double absLatidude = FastMath.abs(point.getLatitude());
         // there are no data in the model for latitudes lower than 15°
         absLatidude = FastMath.max(FastMath.toRadians(15.0), absLatidude);
         // there are no data in the model for latitudes greater than 75°
         absLatidude = FastMath.min(FastMath.toRadians(75.0), absLatidude);
         final double ah = ahAverageFunction.value(absLatidude) - ahAmplitudeFunction.value(absLatidude) * cosCoef;
         final double bh = bhAverageFunction.value(absLatidude) - bhAmplitudeFunction.value(absLatidude) * cosCoef;
         final double ch = chAverageFunction.value(absLatidude) - chAmplitudeFunction.value(absLatidude) * cosCoef;
 
         final double[] function = new double[2];
 
         // Hydrostatic mapping factor
         function[0] = TroposphericModelUtils.mappingFunction(ah, bh, ch, trackingCoordinates.getElevation());
 
         // Wet mapping factor
         function[1] = TroposphericModelUtils.mappingFunction(awFunction.value(absLatidude),
                                                              bwFunction.value(absLatidude),
                                                              cwFunction.value(absLatidude),
                                                              trackingCoordinates.getElevation());
 
         // Apply height correction
         final double correction = TroposphericModelUtils.computeHeightCorrection(trackingCoordinates.getElevation(),
                                                                                  point.getAltitude());
         function[0] = function[0] + correction;
 
         return function;
     }
 
     /** {@inheritDoc} */
     @Override
     @Deprecated
     public <T extends CalculusFieldElement<T>> T[] mappingFactors(final T elevation, final FieldGeodeticPoint<T> point,
                                                                   final FieldAbsoluteDate<T> date) {
         return mappingFactors(new FieldTrackingCoordinates<>(date.getField().getZero(), elevation, date.getField().getZero()),
                               point,
                               new FieldPressureTemperatureHumidity<>(date.getField(),
                                                                      TroposphericModelUtils.STANDARD_ATMOSPHERE),
                               date);
     }
 
     /** {@inheritDoc} */
     @Override
     public <T extends CalculusFieldElement<T>> T[] mappingFactors(final FieldTrackingCoordinates<T> trackingCoordinates,
                                                                   final FieldGeodeticPoint<T> point,
                                                                   final FieldPressureTemperatureHumidity<T> weather,
                                                                   final FieldAbsoluteDate<T> date) {
         final Field<T> field = date.getField();
         final T zero = field.getZero();
 
         // Day of year computation
         final DateTimeComponents dtc = date.getComponents(utc);
         final int dofyear = dtc.getDate().getDayOfYear();
 
         // Temporal factor
         double t0 = 28;
         if (point.getLatitude().getReal() < 0) {
             // southern hemisphere: t0 = 28 + an integer half of year
             t0 += 183;
         }
         final T coef    = zero.getPi().multiply(2.0).multiply((dofyear - t0) / 365.25);
         final T cosCoef = FastMath.cos(coef);
 
         // Compute ah, bh and ch Eq. 5
         double absLatidude = FastMath.abs(point.getLatitude().getReal());
         // there are no data in the model for latitudes lower than 15°
         absLatidude = FastMath.max(FastMath.toRadians(15.0), absLatidude);
         // there are no data in the model for latitudes greater than 75°
         absLatidude = FastMath.min(FastMath.toRadians(75.0), absLatidude);
         final T ah = cosCoef.multiply(ahAmplitudeFunction.value(absLatidude)).negate().add(ahAverageFunction.value(absLatidude));
         final T bh = cosCoef.multiply(bhAmplitudeFunction.value(absLatidude)).negate().add(bhAverageFunction.value(absLatidude));
         final T ch = cosCoef.multiply(chAmplitudeFunction.value(absLatidude)).negate().add(chAverageFunction.value(absLatidude));
 
         final T[] function = MathArrays.buildArray(field, 2);
 
         // Hydrostatic mapping factor
         function[0] = TroposphericModelUtils.mappingFunction(ah, bh, ch,
                                                              trackingCoordinates.getElevation());
 
         // Wet mapping factor
         function[1] = TroposphericModelUtils.mappingFunction(zero.newInstance(awFunction.value(absLatidude)), zero.newInstance(bwFunction.value(absLatidude)),
                                                              zero.newInstance(cwFunction.value(absLatidude)), trackingCoordinates.getElevation());
 
         // Apply height correction
         final T correction = TroposphericModelUtils.computeHeightCorrection(trackingCoordinates.getElevation(),
                                                                             point.getAltitude(),
                                                                             field);
         function[0] = function[0].add(correction);
 
         return function;
     }
 
 }