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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
    * the License.  You may obtain a copy of the License at
    *
    *   http://www.apache.org/licenses/LICENSE-2.0
   *
   * Unless required by applicable law or agreed to in writing, software
   * distributed under the License is distributed on an "AS IS" BASIS,
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   * See the License for the specific language governing permissions and
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  package org.orekit.propagation.conversion.averaging.converters;
  
  import org.orekit.annotation.DefaultDataContext;
  import org.orekit.data.DataContext;
  import org.orekit.frames.Frame;
  import org.orekit.orbits.Orbit;
  import org.orekit.propagation.SpacecraftState;
  import org.orekit.propagation.analytical.tle.TLE;
  import org.orekit.propagation.analytical.tle.generation.FixedPointTleGenerationAlgorithm;
  import org.orekit.time.UTCScale;
  import org.orekit.propagation.conversion.averaging.SGP4OrbitalState;
  
  /**
   * Class for osculating-to-averaged conversion according to "SGP4" theory, meant as the set of
   * models associated to Two-Line Elements.
   *
   * @author Romain Serra
   * @see org.orekit.propagation.analytical.tle.TLEPropagator
   * @see SGP4OrbitalState
   * @since 12.1
   */
  public class OsculatingToSGP4Converter
          extends FixedPointOsculatingToAveragedConverter<SGP4OrbitalState> {
  
      /** First line of arbitrary TLE. Should not impact conversion. */
      private static final String TEMPLATE_LINE_1 = "1 27421U 02021A   02124.48976499 -.00021470  00000-0 -89879-2 0    20";
      /** Second line of arbitrary TLE. Should not impact conversion. */
      private static final String TEMPLATE_LINE_2 = "2 27421  98.7490 199.5121 0001333 133.9522 226.1918 14.26113993    62";
  
      /** Scale for fixed-point algorithm. */
      private final double scale;
      /** UTC time scale. */
      private final UTCScale utc;
      /** TEME frame. */
      private final Frame teme;
  
      /**
       * Constructor with default data context.
       */
      @DefaultDataContext
      public OsculatingToSGP4Converter() {
          this(DataContext.getDefault());
      }
  
      /**
       * Constructor with default parameters for fixed-point algorithm.
       * @param dataContext data context
       */
      public OsculatingToSGP4Converter(final DataContext dataContext) {
          this(DEFAULT_EPSILON, DEFAULT_MAX_ITERATIONS, FixedPointTleGenerationAlgorithm.SCALE_DEFAULT,
                  dataContext);
      }
  
      /**
       * Constructor.
       * @param epsilon convergence threshold
       * @param maxIterations maximum number of iterations
       * @param scale scale
       * @param dataContext data context
       */
      public OsculatingToSGP4Converter(final double epsilon, final int maxIterations,
                                       final double scale, final DataContext dataContext) {
          super(epsilon, maxIterations);
          this.scale = scale;
          this.utc = dataContext.getTimeScales().getUTC();
          this.teme = dataContext.getFrames().getTEME();
      }
  
      /** {@inheritDoc} */
      @Override
      public SGP4OrbitalState convertToAveraged(final Orbit osculatingOrbit) {
          final FixedPointTleGenerationAlgorithm fixedPointAlgorithm = new FixedPointTleGenerationAlgorithm(getEpsilon(),
                  getMaxIterations(), scale, utc, teme);
          final SpacecraftState osculatingState = new SpacecraftState(osculatingOrbit);
          final TLE templateTLe = new TLE(TEMPLATE_LINE_1, TEMPLATE_LINE_2, utc);
          final TLE tle = fixedPointAlgorithm.generate(osculatingState, templateTLe);
          return SGP4OrbitalState.of(tle, teme);
      }
  }