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  package org.orekit.models.earth.troposphere;
  
  import java.util.Collections;
  import java.util.List;
  
  import org.hipparchus.CalculusFieldElement;
  import org.hipparchus.Field;
  import org.hipparchus.util.FastMath;
  import org.hipparchus.util.MathArrays;
  import org.orekit.bodies.FieldGeodeticPoint;
  import org.orekit.bodies.GeodeticPoint;
  import org.orekit.models.earth.weather.ConstantPressureTemperatureHumidityProvider;
  import org.orekit.models.earth.weather.FieldPressureTemperatureHumidity;
  import org.orekit.models.earth.weather.PressureTemperatureHumidity;
  import org.orekit.models.earth.weather.PressureTemperatureHumidityProvider;
  import org.orekit.models.earth.weather.water.CIPM2007;
  import org.orekit.time.AbsoluteDate;
  import org.orekit.time.FieldAbsoluteDate;
  import org.orekit.utils.FieldTrackingCoordinates;
  import org.orekit.utils.ParameterDriver;
  import org.orekit.utils.TrackingCoordinates;
  import org.orekit.utils.units.Unit;
  import org.orekit.utils.units.UnitsConverter;
  
  /** The Mendes - Pavlis tropospheric delay model for optical techniques.
  * It is valid for a wide range of wavelengths from 0.355µm to 1.064µm (Mendes and Pavlis, 2003)
  *
  * @see "Mendes, V. B., & Pavlis, E. C. (2004). High‐accuracy zenith delay prediction at
  *      optical wavelengths. Geophysical Research Letters, 31(14)."
  *
  * @see "Petit, G. and Luzum, B. (eds.), IERS Conventions (2010),
  *      IERS Technical Note No. 36, BKG (2010)"
  *
  * @author Bryan Cazabonne
  */
  public class MendesPavlisModel implements TroposphericModel, TroposphereMappingFunction {
  
      /** Coefficients for the dispersion equation for the hydrostatic component [µm<sup>-2</sup>]. */
      private static final double[] K_COEFFICIENTS = {
          238.0185, 19990.975, 57.362, 579.55174
      };
  
      /** Coefficients for the dispersion equation for the non-hydrostatic component. */
      private static final double[] W_COEFFICIENTS = {
          295.235, 2.6422, -0.032380, 0.004028
      };
  
      /** Coefficients for the mapping function. */
      private static final double[][] A_COEFFICIENTS = {
          {12100.8e-7, 1729.5e-9, 319.1e-7, -1847.8e-11},
          {30496.5e-7, 234.4e-8, -103.5e-6, -185.6e-10},
          {6877.7e-5, 197.2e-7, -345.8e-5, 106.0e-9}
      };
  
      /** Carbon dioxyde content (IAG recommendations). */
      private static final double C02 = 0.99995995;
  
      /** Dispersion equation for the hydrostatic component. */
      private final double fLambdaH;
  
      /** Dispersion equation for the non-hydrostatic component. */
      private final double fLambdaNH;
  
      /** Provider for pressure, temperature and humidity. */
      private final PressureTemperatureHumidityProvider pthProvider;
  
      /** Create a new Mendes-Pavlis model for the troposphere.
       * @param pthProvider provider for atmospheric pressure, temperature and humidity at the station
       * @param lambda laser wavelength
       * @param lambdaUnits units in which {@code lambda} is given
       * @see TroposphericModelUtils#MICRO_M
       * @see TroposphericModelUtils#NANO_M
       * @since 12.1
       * */
      public MendesPavlisModel(final PressureTemperatureHumidityProvider pthProvider,
                               final double lambda, final Unit lambdaUnits) {
          this.pthProvider = pthProvider;
  
          // Dispersion equation for the hydrostatic component
          final double lambdaMicrometer = new UnitsConverter(lambdaUnits, TroposphericModelUtils.MICRO_M).convert(lambda);
          final double sigma  = 1.0 / lambdaMicrometer;
          final double sigma2 = sigma * sigma;
          final double coef1  = K_COEFFICIENTS[0] + sigma2;
         final double coef2  = K_COEFFICIENTS[0] - sigma2;
         final double coef3  = K_COEFFICIENTS[2] + sigma2;
         final double coef4  = K_COEFFICIENTS[2] - sigma2;
         final double frac1 = coef1 / (coef2 * coef2);
         final double frac2 = coef3 / (coef4 * coef4);
         fLambdaH = 0.01 * (K_COEFFICIENTS[1] * frac1 + K_COEFFICIENTS[3] * frac2) * C02;
 
         // Dispersion equation for the non-hydrostatic component
         final double sigma4 = sigma2 * sigma2;
         final double sigma6 = sigma4 * sigma2;
         final double w1s2  = 3 * W_COEFFICIENTS[1] * sigma2;
         final double w2s4  = 5 * W_COEFFICIENTS[2] * sigma4;
         final double w3s6  = 7 * W_COEFFICIENTS[3] * sigma6;
 
         fLambdaNH = 0.003101 * (W_COEFFICIENTS[0] + w1s2 + w2s4 + w3s6);
 
     }
 
     /** Create a new Mendes-Pavlis model using a standard atmosphere model.
      *
      * <ul>
      * <li>altitude: 0m</li>
      * <li>temperature: 18 degree Celsius</li>
      * <li>pressure: 1013.25 hPa</li>
      * <li>humidity: 50%</li>
      * </ul>
      *
      * @param lambda laser wavelength, µm
      * @param lambdaUnits units in which {@code lambda} is given
      * @return a Mendes-Pavlis model with standard environmental values
      * @see TroposphericModelUtils#MICRO_M
      * @see TroposphericModelUtils#NANO_M
      * @since 12.1
      */
     public static MendesPavlisModel getStandardModel(final double lambda, final Unit lambdaUnits) {
         final double h  = 0;
         final double p  = TroposphericModelUtils.HECTO_PASCAL.toSI(1013.25);
         final double t  = 273.15 + 18;
         final double rh = 0.5;
         final PressureTemperatureHumidity pth = new PressureTemperatureHumidity(h, p, t,
                                                                                 new CIPM2007().waterVaporPressure(p, t, rh),
                                                                                 Double.NaN,
                                                                                 Double.NaN);
         return new MendesPavlisModel(new ConstantPressureTemperatureHumidityProvider(pth),
                                      lambda, lambdaUnits);
     }
 
     /** {@inheritDoc} */
     @Override
     public TroposphericDelay pathDelay(final TrackingCoordinates trackingCoordinates,
                                        final GeodeticPoint point,
                                        final double[] parameters, final AbsoluteDate date) {
         // Zenith delay
         final double[] zenithDelay = computeZenithDelay(point, date);
         // Mapping function
         final double[] mappingFunction = mappingFactors(trackingCoordinates, point, date);
         // Tropospheric path delay
         return new TroposphericDelay(zenithDelay[0],
                                      zenithDelay[1],
                                      zenithDelay[0] * mappingFunction[0],
                                      zenithDelay[1] * mappingFunction[1]);
     }
 
     /** {@inheritDoc} */
     @Override
     public <T extends CalculusFieldElement<T>> FieldTroposphericDelay<T> pathDelay(final FieldTrackingCoordinates<T> trackingCoordinates,
                                                                                    final FieldGeodeticPoint<T> point,
                                                                                    final T[] parameters, final FieldAbsoluteDate<T> date) {
         // Zenith delay
         final T[] zenithDelay = computeZenithDelay(point, date);
         // Mapping function
         final T[] mappingFunction = mappingFactors(trackingCoordinates, point, date);
         // Tropospheric path delay
         return new FieldTroposphericDelay<>(zenithDelay[0],
                                             zenithDelay[1],
                                             zenithDelay[0].multiply(mappingFunction[0]),
                                             zenithDelay[1].multiply(mappingFunction[1]));
     }
 
     /**
      * This method allows the  computation of the zenith hydrostatic and
      * zenith wet delay. The resulting element is an array having the following form:
      * <ul>
      * <li>double[0] = D<sub>hz</sub> → zenith hydrostatic delay
      * <li>double[1] = D<sub>wz</sub> → zenith wet delay
      * </ul>
      *
      * @param point station location
      * @param date  current date
      * @return a two components array containing the zenith hydrostatic and wet delays.
      */
     public double[] computeZenithDelay(final GeodeticPoint point, final AbsoluteDate date) {
 
         final PressureTemperatureHumidity pth = pthProvider.getWeatherParameters(point, date);
         final double fsite   = getSiteFunctionValue(point);
 
         // Array for zenith delay
         final double[] delay = new double[2];
 
         // Zenith delay for the hydrostatic component
         // beware since version 12.1 pressure is in Pa and not in hPa, hence the scaling has changed
         delay[0] = pth.getPressure() * 0.00002416579 * (fLambdaH / fsite);
 
         // Zenith delay for the non-hydrostatic component
         // beware since version 12.1 e0 is in Pa and not in hPa, hence the scaling has changed
         delay[1] = 0.000001 * (5.316 * fLambdaNH - 3.759 * fLambdaH) * (pth.getWaterVaporPressure() / fsite);
 
         return delay;
     }
 
     /**
      * This method allows the  computation of the zenith hydrostatic and
      * zenith wet delay. The resulting element is an array having the following form:
      * <ul>
      * <li>T[0] = D<sub>hz</sub> → zenith hydrostatic delay
      * <li>T[1] = D<sub>wz</sub> → zenith wet delay
      * </ul>
      *
      * @param <T>   type of the elements
      * @param point station location
      * @param date  current date
      * @return a two components array containing the zenith hydrostatic and wet delays.
      */
     public <T extends CalculusFieldElement<T>> T[] computeZenithDelay(final FieldGeodeticPoint<T> point,
                                                                       final FieldAbsoluteDate<T> date) {
 
         final FieldPressureTemperatureHumidity<T> pth = pthProvider.getWeatherParameters(point, date);
 
         final T fsite   = getSiteFunctionValue(point);
 
         // Array for zenith delay
         final T[] delay = MathArrays.buildArray(date.getField(), 2);
 
         // Zenith delay for the hydrostatic component
         // beware since version 12.1 pressure is in Pa and not in hPa, hence the scaling has changed
         delay[0] =  pth.getPressure().multiply(0.00002416579).multiply(fLambdaH).divide(fsite);
 
         // Zenith delay for the non-hydrostatic component
         // beware since version 12.1 e0 is in Pa and not in hPa, hence the scaling has changed
         delay[1] = pth.getWaterVaporPressure().divide(fsite).
                    multiply(0.000001 * (5.316 * fLambdaNH - 3.759 * fLambdaH));
 
         return delay;
 
     }
 
     /** With the Mendes Pavlis tropospheric model, the mapping
      * function is not split into hydrostatic and wet component.
      * <p>
      * Therefore, the two components of the resulting array are equals.
      * <ul>
      * <li>double[0] = m(e) → total mapping function
      * <li>double[1] = m(e) → total mapping function
      * </ul>
      * <p>
      * The total delay will thus be computed as:<br>
      * δ = D<sub>hz</sub> * m(e) + D<sub>wz</sub> * m(e)<br>
      * δ = (D<sub>hz</sub> + D<sub>wz</sub>) * m(e) = δ<sub>z</sub> * m(e)
      */
     @Override
     public double[] mappingFactors(final TrackingCoordinates trackingCoordinates,
                                    final GeodeticPoint point,
                                    final AbsoluteDate date) {
         final double sinE = FastMath.sin(trackingCoordinates.getElevation());
 
         final PressureTemperatureHumidity pth = pthProvider.getWeatherParameters(point, date);
         final double T2degree = pth.getTemperature() - 273.15;
 
         // Mapping function coefficients
         final double a1 = computeMFCoeffient(A_COEFFICIENTS[0][0], A_COEFFICIENTS[0][1],
                                              A_COEFFICIENTS[0][2], A_COEFFICIENTS[0][3],
                                              T2degree, point);
         final double a2 = computeMFCoeffient(A_COEFFICIENTS[1][0], A_COEFFICIENTS[1][1],
                                              A_COEFFICIENTS[1][2], A_COEFFICIENTS[1][3],
                                              T2degree, point);
         final double a3 = computeMFCoeffient(A_COEFFICIENTS[2][0], A_COEFFICIENTS[2][1],
                                              A_COEFFICIENTS[2][2], A_COEFFICIENTS[2][3],
                                              T2degree, point);
 
         // Numerator
         final double numMP = 1 + a1 / (1 + a2 / (1 + a3));
         // Denominator
         final double denMP = sinE + a1 / (sinE + a2 / (sinE + a3));
 
         final double factor = numMP / denMP;
 
         return new double[] {
             factor,
             factor
         };
     }
 
     /** With the Mendes Pavlis tropospheric model, the mapping
      * function is not split into hydrostatic and wet component.
      * <p>
      * Therefore, the two components of the resulting array are equals.
      * <ul>
      * <li>double[0] = m(e) → total mapping function
      * <li>double[1] = m(e) → total mapping function
      * </ul>
      * <p>
      * The total delay will thus be computed as:<br>
      * δ = D<sub>hz</sub> * m(e) + D<sub>wz</sub> * m(e)<br>
      * δ = (D<sub>hz</sub> + D<sub>wz</sub>) * m(e) = δ<sub>z</sub> * m(e)
      */
     @Override
     public <T extends CalculusFieldElement<T>> T[] mappingFactors(final FieldTrackingCoordinates<T> trackingCoordinates,
                                                                   final FieldGeodeticPoint<T> point,
                                                                   final FieldAbsoluteDate<T> date) {
         final Field<T> field = date.getField();
 
         final T sinE = FastMath.sin(trackingCoordinates.getElevation());
 
         final FieldPressureTemperatureHumidity<T> pth = pthProvider.getWeatherParameters(point, date);
         final T T2degree = pth.getTemperature().subtract(273.15);
 
         // Mapping function coefficients
         final T a1 = computeMFCoeffient(A_COEFFICIENTS[0][0], A_COEFFICIENTS[0][1],
                                         A_COEFFICIENTS[0][2], A_COEFFICIENTS[0][3],
                                         T2degree, point);
         final T a2 = computeMFCoeffient(A_COEFFICIENTS[1][0], A_COEFFICIENTS[1][1],
                                         A_COEFFICIENTS[1][2], A_COEFFICIENTS[1][3],
                                         T2degree, point);
         final T a3 = computeMFCoeffient(A_COEFFICIENTS[2][0], A_COEFFICIENTS[2][1],
                                         A_COEFFICIENTS[2][2], A_COEFFICIENTS[2][3],
                                         T2degree, point);
 
         // Numerator
         final T numMP = a1.divide(a2.divide(a3.add(1.0)).add(1.0)).add(1.0);
         // Denominator
         final T denMP = a1.divide(a2.divide(a3.add(sinE)).add(sinE)).add(sinE);
 
         final T factor = numMP.divide(denMP);
 
         final T[] mapping = MathArrays.buildArray(field, 2);
         mapping[0] = factor;
         mapping[1] = factor;
 
         return mapping;
     }
 
     /** {@inheritDoc} */
     @Override
     public List<ParameterDriver> getParametersDrivers() {
         return Collections.emptyList();
     }
 
     /** Get the site parameter.
      *
      * @param point station location
      * @return the site parameter.
      */
     private double getSiteFunctionValue(final GeodeticPoint point) {
         return 1. - 0.00266 * FastMath.cos(2. * point.getLatitude()) - 0.00000028 * point.getAltitude();
     }
 
     /** Get the site parameter.
      *
      * @param <T> type of the elements
      * @param point station location
      * @return the site parameter.
      */
     private <T extends CalculusFieldElement<T>> T getSiteFunctionValue(final FieldGeodeticPoint<T> point) {
         return FastMath.cos(point.getLatitude().multiply(2.)).multiply(0.00266).add(point.getAltitude().multiply(0.00000028)).negate().add(1.);
     }
 
     /** Compute the coefficients of the Mapping Function.
      *
      * @param t the temperature at the station site, °C
      * @param a0 first coefficient
      * @param a1 second coefficient
      * @param a2 third coefficient
      * @param a3 fourth coefficient
      * @param point station location
      * @return the value of the coefficient
      */
     private double computeMFCoeffient(final double a0, final double a1, final double a2, final double a3,
                                       final double t, final GeodeticPoint point) {
         return a0 + a1 * t + a2 * FastMath.cos(point.getLatitude()) + a3 * point.getAltitude();
     }
 
     /** Compute the coefficients of the Mapping Function.
      *
      * @param <T> type of the elements
      * @param t the temperature at the station site, °C
      * @param a0 first coefficient
      * @param a1 second coefficient
      * @param a2 third coefficient
      * @param a3 fourth coefficient
      * @param point station location
      * @return the value of the coefficient
      */
     private <T extends CalculusFieldElement<T>> T computeMFCoeffient(final double a0, final double a1, final double a2, final double a3,
                                                                      final T t, final FieldGeodeticPoint<T> point) {
         return point.getAltitude().multiply(a3).add(FastMath.cos(point.getLatitude()).multiply(a2)).add(t.multiply(a1).add(a0));
     }
 
 }