SubFrame4E.java

  1. /* Copyright 2002-2024 Thales Alenia Space
  2.  * Licensed to CS GROUP (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.gnss.rflink.gps;

  19. import org.hipparchus.util.MathUtils;

  21. /**
  22.  * Container for sub-frames 4, page 25.
  23.  * <p>
  24.  * Table 20-1, sheet 9 and table 40-1, sheet 9 in
  25.  * <a href="https://navcen.uscg.gov/sites/default/files/pdf/gps/IS-GPS-200N.pdf">NAVSTAR
  26.  * GPS Space Segment/Navigation User Segment Interface</a>, IS-GPS-200N, 22 Aug 2022
  27.  * </p>
  28.  * @author Luc Maisonobe
  29.  * @since 12.0
  30.  */
  31. public class SubFrame4E extends SubFrame45 {

  33.     /** Number of Anti-spoofing entries. */
  34.     public static final int NB_AS = 32;

  36.     /** Number of SV health entries. */
  37.     public static final int NB_SVH = 8;

  39.     /** Size of Anti-spoofing. */
  40.     private static final int AS_SIZE = 4;

  42.     /** Size of SV Health. */
  43.     private static final int SVH_SIZE = 6;

  45.     /** Index of first AS field. */
  46.     private static final int FIRST_AS = 9;

  48.     /** Index of reserved field in word 8. */
  49.     private static final int RESERVED_8 = FIRST_AS + NB_AS;

  51.     /** Index of reserved field in word 10. */
  52.     private static final int RESERVED_10 = RESERVED_8 + 1 + NB_AS + NB_SVH;

  54.     /** Simple constructor.
  55.      * @param words raw words
  56.      */
  57.     SubFrame4E(final int[] words) {

  59.         // create raw container
  60.         super(words, RESERVED_10 + 1);

  62.         // populate container
  63.         int field = FIRST_AS - 1;
  64.         int word  = 3;
  65.         int shift = 22;

  67.         // anti-spoofing
  68.         for (int i = 0; i < NB_AS; ++i) {
  69.             if (shift >= AS_SIZE + PARITY_SIZE) {
  70.                 // current word contains a complete AS
  71.                 shift -= AS_SIZE;
  72.                 setField(++field, word, shift, AS_SIZE, words);
  73.             } else {
  74.                 // current word is exhausted
  75.                 shift = WORD_SIZE - AS_SIZE;
  76.                 setField(++field, ++word, shift, AS_SIZE, words);
  77.             }
  78.         }

  80.         // 2 bits for system use
  81.         shift -= 2;
  82.         setField(RESERVED_8, word, shift, 2, words);

  84.         // SV health
  85.         for (int i = 0; i < NB_SVH; ++i) {
  86.             if (shift >= SVH_SIZE + PARITY_SIZE) {
  87.                 // current word contains a complete SVH
  88.                 shift -= SVH_SIZE;
  89.                 setField(++field, word, shift, SVH_SIZE, words);
  90.             } else {
  91.                 // current word is exhausted
  92.                 shift = WORD_SIZE - SVH_SIZE;
  93.                 setField(++field, ++word, shift, SVH_SIZE, words);
  94.             }
  95.         }

  97.         setField(RESERVED_10, 10,  8, 4, words);

  99.     }

  101.     /** Get the anti-spoofing for a satellite.
  102.      * @param index in the sub-frame (from 1 to 32, beware it is not the satellite number,
  103.      * it is also related to {@link #getDataId()})
  104.      * @return anti-spoofing
  105.      */
  106.     public int getAntiSpoofing(final int index) {
  107.         MathUtils.checkRangeInclusive(index, 1, NB_AS);
  108.         return getField(FIRST_AS + index - 1);
  109.     }

  111.     /** Get the reserved field in word 8.
  112.      * @return reserved field in word 8
  113.      */
  114.     public int getReserved8() {
  115.         return getField(RESERVED_8);
  116.     }

  118.     /** Get the Sv health for a satellite.
  119.      * @param index in the sub-frame (from 1 to 7 or 1 to 8 depending on
  120.      * {@link #getDataId()}, beware it is not the satellite number,
  121.      * it is also related to {@link #getDataId()}), an
  122.      * @return anti-spoofing
  123.      */
  124.     public int getSvHealth(final int index) {
  125.         MathUtils.checkRangeInclusive(index, 1, NB_SVH);
  126.         return getField(RESERVED_8 + index);
  127.     }

  129.     /** Get the reserved field in word 10.
  130.      * @return reserved field in word 10
  131.      */
  132.     public int getReserved10() {
  133.         return getField(RESERVED_10);
  134.     }

  136. }
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