GeoMagneticModelLoader.java

  1. /* Copyright 2011-2012 Space Applications Services
  2.  * Licensed to CS Communication & Systèmes (CS) under one or more
  3.  * contributor license agreements.  See the NOTICE file distributed with
  4.  * this work for additional information regarding copyright ownership.
  5.  * CS licenses this file to You under the Apache License, Version 2.0
  6.  * (the "License"); you may not use this file except in compliance with
  7.  * the License.  You may obtain a copy of the License at
  8.  *
  9.  *   http://www.apache.org/licenses/LICENSE-2.0
  10.  *
  11.  * Unless required by applicable law or agreed to in writing, software
  12.  * distributed under the License is distributed on an "AS IS" BASIS,
  13.  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  14.  * See the License for the specific language governing permissions and
  15.  * limitations under the License.
  16.  */
  17. package org.orekit.models.earth;

  19. import java.io.IOException;
  20. import java.io.InputStream;
  21. import java.io.InputStreamReader;
  22. import java.io.StreamTokenizer;
  23. import java.text.ParseException;
  24. import java.util.Collection;
  25. import java.util.LinkedList;
  26. import java.util.List;

  28. import org.orekit.data.DataLoader;

  30. /** Loads geomagnetic field models from a given input stream. A stream may contain multiple
  31.  * models, the loader reads all available models in consecutive order.
  32.  * <p>
  33.  * The format of the expected model file is either:
  34.  * <ul>
  35.  *   <li>combined format as used by the geomag software, available from the
  36.  *       <a href="http://www.ngdc.noaa.gov/IAGA/vmod/igrf.html">IGRF model site</a>;
  37.  *       supports multiple epochs per file</li>
  38.  *   <li>original format as used by the
  39.  *       <a href="http://www.ngdc.noaa.gov/geomag/WMM/DoDWMM.shtml">WMM model site</a>.
  40.  * </ul>
  41.  * <p>
  42.  * <b>Combined Format</b>
  43.  * <pre>
  44.  *     {model name} {epoch} {nMax} {nMaxSec} {nMax3} {validity start} {validity end} {minAlt} {maxAlt} {model name} {line number}
  45.  * {n} {m} {gnm} {hnm} {dgnm} {dhnm} {model name} {line number}
  46.  * </pre>
  47.  * <p>
  48.  * Example:
  49.  * </p>
  50.  * <pre>
  51.  *    WMM2010  2010.00 12 12  0 2010.00 2015.00   -1.0  600.0          WMM2010   0
  52.  * 1  0  -29496.6       0.0      11.6       0.0                        WMM2010   1
  53.  * 1  1   -1586.3    4944.4      16.5     -25.9                        WMM2010   2
  54.  * </pre>
  55.  * <p>
  56.  * <b>Original WMM Format</b>
  57.  * <pre>
  58.  *    {epoch} {model name} {validity start}
  59.  * {n} {m} {gnm} {hnm} {dgnm} {dhnm}
  60.  * </pre>
  61.  * <p>
  62.  * Example:
  63.  * </p>
  64.  * <pre>
  65.  *    2015.0            WMM-2015        12/15/2014
  66.  *  1  0  -29438.5       0.0       10.7        0.0
  67.  *  1  1   -1501.1    4796.2       17.9      -26.8
  68.  * </pre>
  69.  *
  70.  * @author Thomas Neidhart
  71.  */
  72. public class GeoMagneticModelLoader implements DataLoader {

  74.     /** The loaded models. */
  75.     private List<GeoMagneticField> models = new LinkedList<GeoMagneticField>();

  77.     /** Returns a {@link Collection} of the {@link GeoMagneticField} models that
  78.      * have been successfully loaded. The {@link Collection} is in
  79.      * insertion-order, thus it may not be sorted in order of the model epoch.
  80.      * @return a {@link Collection} of {@link GeoMagneticField} models
  81.      */
  82.     public Collection<GeoMagneticField> getModels() {
  83.         return models;
  84.     }

  86.     /** {@inheritDoc} */
  87.     public boolean stillAcceptsData() {
  88.         return models == null || models.isEmpty();
  89.     }

  91.     /** {@inheritDoc} */
  92.     public void loadData(final InputStream input, final String name)
  93.         throws IOException, ParseException {

  95.         // open data file and parse values
  96.         final StreamTokenizer str = new StreamTokenizer(new InputStreamReader(input, "UTF-8"));

  98.         while (true) {
  99.             final GeoMagneticField model = readModel(str);
  100.             if (model != null) {
  101.                 models.add(model);
  102.             } else {
  103.                 break;
  104.             }
  105.         }
  106.     }

  108.     /** Read the model from the given {@link StreamTokenizer}.
  109.      * @param stream the stream to read the model from
  110.      * @return the parsed geomagnetic field model
  111.      * @throws IOException if an I/O error occurs
  112.      */
  113.     private GeoMagneticField readModel(final StreamTokenizer stream) throws IOException {

  115.         // check whether there is another model available in the stream
  116.         final int ttype = stream.nextToken();
  117.         if (ttype == StreamTokenizer.TT_EOF) {
  118.             return null;
  119.         }

  121.         if (ttype == StreamTokenizer.TT_WORD) {
  122.             return readCombinedFormat(stream);
  123.         } else {
  124.             return readOriginalWMMFormat(stream);
  125.         }
  126.     }

  128.     /** Read a magnetic field from combined format.
  129.      * @param stream the stream to read the model from
  130.      * @return magnetic field
  131.      * @throws IOException if some read error occurs
  132.      */
  133.     private GeoMagneticField readCombinedFormat(final StreamTokenizer stream)
  134.         throws IOException {
  135.         final String modelName = stream.sval;
  136.         stream.nextToken();
  137.         final double epoch = stream.nval;
  138.         stream.nextToken();
  139.         final int nMax = (int) stream.nval;
  140.         stream.nextToken();
  141.         final int nMaxSecVar = (int) stream.nval;

  143.         // ignored
  144.         stream.nextToken();

  146.         stream.nextToken();
  147.         final double startYear = stream.nval;

  149.         stream.nextToken();
  150.         final double endYear = stream.nval;

  152.         final GeoMagneticField model = new GeoMagneticField(modelName, epoch, nMax, nMaxSecVar,
  153.                                                             startYear, endYear);

  155.         // the rest is ignored
  156.         stream.nextToken();
  157.         @SuppressWarnings("unused")
  158.         final double altmin = stream.nval;

  160.         stream.nextToken();
  161.         @SuppressWarnings("unused")
  162.         final double altmax = stream.nval;

  164.         stream.nextToken();
  165.         stream.nextToken();

  167.         // loop to get model data from file
  168.         boolean done = false;
  169.         int n;
  170.         int m;

  172.         do {
  173.             stream.nextToken();
  174.             n = (int) stream.nval;
  175.             stream.nextToken();
  176.             m = (int) stream.nval;

  178.             stream.nextToken();
  179.             final double gnm = stream.nval;
  180.             stream.nextToken();
  181.             final double hnm = stream.nval;
  182.             stream.nextToken();
  183.             final double dgnm = stream.nval;
  184.             stream.nextToken();
  185.             final double dhnm = stream.nval;

  187.             model.setMainFieldCoefficients(n, m, gnm, hnm);
  188.             if (n <= nMaxSecVar && m <= nMaxSecVar) {
  189.                 model.setSecularVariationCoefficients(n, m, dgnm, dhnm);
  190.             }

  192.             stream.nextToken();
  193.             stream.nextToken();

  195.             done = n == nMax && m == nMax;
  196.         } while (!done);

  198.         return model;
  199.     }

  201.     /** Read a magnetic field from original WMM files.
  202.      * @param stream the stream to read the model from
  203.      * @return magnetic field
  204.      * @throws IOException if some read error occurs
  205.      */
  206.     private GeoMagneticField readOriginalWMMFormat(final StreamTokenizer stream)
  207.         throws IOException {

  209.         // hard-coded values in original WMM format
  210.         final int nMax = 12;
  211.         final int nMaxSecVar = 12;

  213.         // the validity start is encoded in format MM/dd/yyyy
  214.         // use the slash as whitespace character to get separate tokens
  215.         stream.whitespaceChars('/', '/');

  217.         final double epoch = stream.nval;
  218.         stream.nextToken();
  219.         final String modelName = stream.sval;
  220.         stream.nextToken();
  221.         final double month = stream.nval;
  222.         stream.nextToken();
  223.         final double day = stream.nval;
  224.         stream.nextToken();
  225.         final double year = stream.nval;

  227.         final double startYear = GeoMagneticField.getDecimalYear((int) day, (int) month, (int) year);

  229.         final GeoMagneticField model = new GeoMagneticField(modelName, epoch, nMax, nMaxSecVar,
  230.                                                             startYear, epoch + 5.0);

  232.         // loop to get model data from file
  233.         boolean done = false;
  234.         int n;
  235.         int m;

  237.         do {
  238.             stream.nextToken();
  239.             n = (int) stream.nval;
  240.             stream.nextToken();
  241.             m = (int) stream.nval;

  243.             stream.nextToken();
  244.             final double gnm = stream.nval;
  245.             stream.nextToken();
  246.             final double hnm = stream.nval;
  247.             stream.nextToken();
  248.             final double dgnm = stream.nval;
  249.             stream.nextToken();
  250.             final double dhnm = stream.nval;

  252.             model.setMainFieldCoefficients(n, m, gnm, hnm);
  253.             if (n <= nMaxSecVar && m <= nMaxSecVar) {
  254.                 model.setSecularVariationCoefficients(n, m, dgnm, dhnm);
  255.             }

  257.             done = n == nMax && m == nMax;
  258.         } while (!done);

  260.         // the original format closes with two delimiting lines of '9's
  261.         stream.nextToken();
  262.         stream.nextToken();

  264.         return model;
  265.     }

  267. }
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