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    * CS licenses this file to You under the Apache License, Version 2.0
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    *
    *   http://www.apache.org/licenses/LICENSE-2.0
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   * Unless required by applicable law or agreed to in writing, software
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  package org.orekit.models.earth.troposphere;
  
  import org.hipparchus.util.FastMath;
  import org.hipparchus.util.Precision;
  import org.junit.Assert;
  import org.junit.Before;
  import org.junit.BeforeClass;
  import org.junit.Test;
  import org.orekit.Utils;
  import org.orekit.bodies.GeodeticPoint;
  import org.orekit.errors.OrekitException;
  import org.orekit.time.AbsoluteDate;
  import org.orekit.time.TimeScalesFactory;
  
  public class NiellMappingFunctionModelTest {
  
      @BeforeClass
      public static void setUpGlobal() {
          Utils.setDataRoot("atmosphere");
      }
  
      @Before
      public void setUp() throws OrekitException {
          Utils.setDataRoot("regular-data:potential/shm-format");
      }
  
      @Test
      public void testMappingFactors() {
          
          // Site (Le Mans, France):      latitude:  48.0°
          //                              longitude: 0.20°
          //                              height:    68 m
          //
          // Date: 1st January 1994 at 0h UT
          //
          // Ref:    Mercier F., Perosanz F., Mesures GNSS, Résolution des ambiguités.
          //
          // Expected mapping factors : hydrostatic -> 10.16 (Ref)
          //                                    wet -> 10.75 (Ref)
  
          final AbsoluteDate date = new AbsoluteDate(1994, 1, 1, TimeScalesFactory.getUTC());
          
          final double latitude    = FastMath.toRadians(48.0);
          final double longitude   = FastMath.toRadians(0.20);
          final double height      = 68.0;
          final GeodeticPoint point = new GeodeticPoint(latitude, longitude, height);
  
          final double elevation     = FastMath.toRadians(5.0);
          final double expectedHydro = 10.16;
          final double expectedWet   = 10.75;
  
          final MappingFunction model = new NiellMappingFunctionModel();
          
          final double[] computedMapping = model.mappingFactors(elevation, point, date);
          
          Assert.assertEquals(expectedHydro, computedMapping[0], 1.0e-2);
          Assert.assertEquals(expectedWet,   computedMapping[1], 1.0e-2);
      }
  
      @Test
      public void testFixedHeight() {
          final AbsoluteDate date = new AbsoluteDate();
          final GeodeticPoint point = new GeodeticPoint(FastMath.toRadians(45.0), FastMath.toRadians(45.0), 350.0);
          MappingFunction model = new NiellMappingFunctionModel();
          double[] lastFactors = new double[] {
              Double.MAX_VALUE,
              Double.MAX_VALUE
          };
          // mapping functions shall decline with increasing elevation angle
          for (double elev = 10d; elev < 90d; elev += 8d) {
              final double[] factors = model.mappingFactors(FastMath.toRadians(elev), point, date);
              Assert.assertTrue(Precision.compareTo(factors[0], lastFactors[0], 1.0e-6) < 0);
              Assert.assertTrue(Precision.compareTo(factors[1], lastFactors[1], 1.0e-6) < 0);
              lastFactors[0] = factors[0];
              lastFactors[1] = factors[1];
          }
      }
  
  }