NeQuickModel.java
/* Copyright 2002-2020 CS GROUP
* Licensed to CS GROUP (CS) under one or more
* contributor license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright ownership.
* 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,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package org.orekit.models.earth.ionosphere;
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.nio.charset.StandardCharsets;
import java.util.Collections;
import java.util.List;
import java.util.regex.Pattern;
import org.hipparchus.Field;
import org.hipparchus.RealFieldElement;
import org.hipparchus.util.FastMath;
import org.hipparchus.util.FieldSinCos;
import org.hipparchus.util.MathArrays;
import org.hipparchus.util.SinCos;
import org.orekit.annotation.DefaultDataContext;
import org.orekit.bodies.BodyShape;
import org.orekit.bodies.FieldGeodeticPoint;
import org.orekit.bodies.GeodeticPoint;
import org.orekit.data.DataContext;
import org.orekit.errors.OrekitException;
import org.orekit.errors.OrekitMessages;
import org.orekit.frames.TopocentricFrame;
import org.orekit.propagation.FieldSpacecraftState;
import org.orekit.propagation.SpacecraftState;
import org.orekit.time.AbsoluteDate;
import org.orekit.time.DateComponents;
import org.orekit.time.DateTimeComponents;
import org.orekit.time.FieldAbsoluteDate;
import org.orekit.time.TimeScale;
import org.orekit.utils.ParameterDriver;
import org.orekit.utils.TimeStampedFieldPVCoordinates;
import org.orekit.utils.TimeStampedPVCoordinates;
/**
* NeQuick ionospheric delay model.
*
* @author Bryan Cazabonne
*
* @see "European Union (2016). European GNSS (Galileo) Open Service-Ionospheric Correction
* Algorithm for Galileo Single Frequency Users. 1.2."
*
* @since 10.1
*/
public class NeQuickModel implements IonosphericModel {
/** NeQuick resources base directory. */
private static final String NEQUICK_BASE = "/assets/org/orekit/nequick/";
/** Serializable UID. */
private static final long serialVersionUID = 201928051L;
/** Pattern for delimiting regular expressions. */
private static final Pattern SEPARATOR = Pattern.compile("\\s+");
/** Mean Earth radius in m (Ref Table 2.5.2). */
private static final double RE = 6371200.0;
/** Meters to kilometers converter. */
private static final double M_TO_KM = 0.001;
/** Factor for the electron density computation. */
private static final double DENSITY_FACTOR = 1.0e11;
/** Factor for the path delay computation. */
private static final double DELAY_FACTOR = 40.3e16;
/** The three ionospheric coefficients broadcast in the Galileo navigation message. */
private final double[] alpha;
/** MODIP grid. */
private final double[][] stModip;
/** Month used for loading CCIR coefficients. */
private int month;
/** F2 coefficients used by the F2 layer. */
private double[][][] f2;
/** Fm3 coefficients used by the F2 layer. */
private double[][][] fm3;
/** UTC time scale. */
private final TimeScale utc;
/**
* Build a new instance.
*
* <p>This constructor uses the {@link DataContext#getDefault() default data context}.
*
* @param alpha effective ionisation level coefficients
* @see #NeQuickModel(double[], TimeScale)
*/
@DefaultDataContext
public NeQuickModel(final double[] alpha) {
this(alpha, DataContext.getDefault().getTimeScales().getUTC());
}
/**
* Build a new instance.
* @param alpha effective ionisation level coefficients
* @param utc UTC time scale.
* @since 10.1
*/
public NeQuickModel(final double[] alpha,
final TimeScale utc) {
// F2 layer values
this.month = 0;
this.f2 = null;
this.fm3 = null;
// Read modip grid
final MODIPLoader parser = new MODIPLoader();
parser.loadMODIPGrid();
this.stModip = parser.getMODIPGrid();
// Ionisation level coefficients
this.alpha = alpha.clone();
this.utc = utc;
}
@Override
public double pathDelay(final SpacecraftState state, final TopocentricFrame baseFrame,
final double frequency, final double[] parameters) {
// Point
final GeodeticPoint recPoint = baseFrame.getPoint();
// Date
final AbsoluteDate date = state.getDate();
// Reference body shape
final BodyShape ellipsoid = baseFrame.getParentShape();
// Satellite geodetic coordinates
final TimeStampedPVCoordinates pv = state.getPVCoordinates(ellipsoid.getBodyFrame());
final GeodeticPoint satPoint = ellipsoid.transform(pv.getPosition(), ellipsoid.getBodyFrame(), state.getDate());
// Total Electron Content
final double tec = stec(date, recPoint, satPoint);
// Ionospheric delay
final double factor = DELAY_FACTOR / (frequency * frequency);
return factor * tec;
}
@Override
public <T extends RealFieldElement<T>> T pathDelay(final FieldSpacecraftState<T> state, final TopocentricFrame baseFrame,
final double frequency, final T[] parameters) {
// Date
final FieldAbsoluteDate<T> date = state.getDate();
// Point
final FieldGeodeticPoint<T> recPoint = baseFrame.getPoint(date.getField());
// Reference body shape
final BodyShape ellipsoid = baseFrame.getParentShape();
// Satellite geodetic coordinates
final TimeStampedFieldPVCoordinates<T> pv = state.getPVCoordinates(ellipsoid.getBodyFrame());
final FieldGeodeticPoint<T> satPoint = ellipsoid.transform(pv.getPosition(), ellipsoid.getBodyFrame(), state.getDate());
// Total Electron Content
final T tec = stec(date, recPoint, satPoint);
// Ionospheric delay
final double factor = DELAY_FACTOR / (frequency * frequency);
return tec.multiply(factor);
}
@Override
public List<ParameterDriver> getParametersDrivers() {
return Collections.emptyList();
}
/**
* This method allows the computation of the Stant Total Electron Content (STEC).
* <p>
* This method follows the Gauss algorithm exposed in section 2.5.8.2.8 of
* the reference document.
* </p>
* @param date current date
* @param recP receiver position
* @param satP satellite position
* @return the STEC in TECUnits
*/
public double stec(final AbsoluteDate date, final GeodeticPoint recP, final GeodeticPoint satP) {
// Ray-perigee parameters
final Ray ray = new Ray(recP, satP);
// Load the correct CCIR file
final DateTimeComponents dateTime = date.getComponents(utc);
loadsIfNeeded(dateTime.getDate());
// Tolerance for the integration accuracy. Defined inside the reference document, section 2.5.8.1.
final double h1 = recP.getAltitude();
final double tolerance;
if (h1 < 1000000.0) {
tolerance = 0.001;
} else {
tolerance = 0.01;
}
// Integration
int n = 8;
final Segment seg1 = new Segment(n, ray);
double gn1 = stecIntegration(seg1, dateTime);
n *= 2;
final Segment seg2 = new Segment(n, ray);
double gn2 = stecIntegration(seg2, dateTime);
int count = 1;
while (FastMath.abs(gn2 - gn1) > tolerance * FastMath.abs(gn1) && count < 20) {
gn1 = gn2;
n *= 2;
final Segment seg = new Segment(n, ray);
gn2 = stecIntegration(seg, dateTime);
count += 1;
}
// If count > 20 the integration did not converge
if (count == 20) {
throw new OrekitException(OrekitMessages.STEC_INTEGRATION_DID_NOT_CONVERGE);
}
// Eq. 202
return (gn2 + ((gn2 - gn1) / 15.0)) * 1.0e-16;
}
/**
* This method allows the computation of the Stant Total Electron Content (STEC).
* <p>
* This method follows the Gauss algorithm exposed in section 2.5.8.2.8 of
* the reference document.
* </p>
* @param <T> type of the elements
* @param date current date
* @param recP receiver position
* @param satP satellite position
* @return the STEC in TECUnits
*/
public <T extends RealFieldElement<T>> T stec(final FieldAbsoluteDate<T> date,
final FieldGeodeticPoint<T> recP,
final FieldGeodeticPoint<T> satP) {
// Field
final Field<T> field = date.getField();
// Ray-perigee parameters
final FieldRay<T> ray = new FieldRay<>(field, recP, satP);
// Load the correct CCIR file
final DateTimeComponents dateTime = date.getComponents(utc);
loadsIfNeeded(dateTime.getDate());
// Tolerance for the integration accuracy. Defined inside the reference document, section 2.5.8.1.
final T h1 = recP.getAltitude();
final double tolerance;
if (h1.getReal() < 1000000.0) {
tolerance = 0.001;
} else {
tolerance = 0.01;
}
// Integration
int n = 8;
final FieldSegment<T> seg1 = new FieldSegment<>(field, n, ray);
T gn1 = stecIntegration(field, seg1, dateTime);
n *= 2;
final FieldSegment<T> seg2 = new FieldSegment<>(field, n, ray);
T gn2 = stecIntegration(field, seg2, dateTime);
int count = 1;
while (FastMath.abs(gn2.subtract(gn1)).getReal() > FastMath.abs(gn1).multiply(tolerance).getReal() && count < 20) {
gn1 = gn2;
n *= 2;
final FieldSegment<T> seg = new FieldSegment<>(field, n, ray);
gn2 = stecIntegration(field, seg, dateTime);
count += 1;
}
// If count > 20 the integration did not converge
if (count == 20) {
throw new OrekitException(OrekitMessages.STEC_INTEGRATION_DID_NOT_CONVERGE);
}
// Eq. 202
return gn2.add(gn2.subtract(gn1).divide(15.0)).multiply(1.0e-16);
}
/**
* This method perfoms the STEC integration.
* @param seg coordinates along the integration path
* @param dateTime current date and time componentns
* @return result of the integration
*/
private double stecIntegration(final Segment seg, final DateTimeComponents dateTime) {
// Integration points
final double[] heightS = seg.getHeights();
final double[] latitudeS = seg.getLatitudes();
final double[] longitudeS = seg.getLongitudes();
// Compute electron density
double density = 0.0;
for (int i = 0; i < heightS.length; i++) {
final NeQuickParameters parameters = new NeQuickParameters(dateTime, f2, fm3,
latitudeS[i], longitudeS[i],
alpha, stModip);
density += electronDensity(heightS[i], parameters);
}
return 0.5 * seg.getInterval() * density;
}
/**
* This method perfoms the STEC integration.
* @param <T> type of the elements
* @param field field of the elements
* @param seg coordinates along the integration path
* @param dateTime current date and time componentns
* @return result of the integration
*/
private <T extends RealFieldElement<T>> T stecIntegration(final Field<T> field,
final FieldSegment<T> seg,
final DateTimeComponents dateTime) {
// Integration points
final T[] heightS = seg.getHeights();
final T[] latitudeS = seg.getLatitudes();
final T[] longitudeS = seg.getLongitudes();
// Compute electron density
T density = field.getZero();
for (int i = 0; i < heightS.length; i++) {
final FieldNeQuickParameters<T> parameters = new FieldNeQuickParameters<>(field, dateTime, f2, fm3,
latitudeS[i], longitudeS[i],
alpha, stModip);
density = density.add(electronDensity(field, heightS[i], parameters));
}
return seg.getInterval().multiply(density).multiply(0.5);
}
/**
* Computes the electron density at a given height.
* @param h height in m
* @param parameters NeQuick model parameters
* @return electron density [m^-3]
*/
private double electronDensity(final double h, final NeQuickParameters parameters) {
// Convert height in kilometers
final double hInKm = h * M_TO_KM;
// Electron density
final double n;
if (hInKm <= parameters.getHmF2()) {
n = bottomElectronDensity(hInKm, parameters);
} else {
n = topElectronDensity(hInKm, parameters);
}
return n;
}
/**
* Computes the electron density at a given height.
* @param <T> type of the elements
* @param field field of the elements
* @param h height in m
* @param parameters NeQuick model parameters
* @return electron density [m^-3]
*/
private <T extends RealFieldElement<T>> T electronDensity(final Field<T> field,
final T h,
final FieldNeQuickParameters<T> parameters) {
// Convert height in kilometers
final T hInKm = h.multiply(M_TO_KM);
// Electron density
final T n;
if (hInKm.getReal() <= parameters.getHmF2().getReal()) {
n = bottomElectronDensity(field, hInKm, parameters);
} else {
n = topElectronDensity(field, hInKm, parameters);
}
return n;
}
/**
* Computes the electron density of the bottomside.
* @param h height in km
* @param parameters NeQuick model parameters
* @return the electron density N in m-3
*/
private double bottomElectronDensity(final double h, final NeQuickParameters parameters) {
// Select the relevant B parameter for the current height (Eq. 109 and 110)
final double be;
if (h > parameters.getHmE()) {
be = parameters.getBETop();
} else {
be = parameters.getBEBot();
}
final double bf1;
if (h > parameters.getHmF1()) {
bf1 = parameters.getB1Top();
} else {
bf1 = parameters.getB1Bot();
}
final double bf2 = parameters.getB2Bot();
// Useful array of constants
final double[] ct = new double[] {
1.0 / bf2, 1.0 / bf1, 1.0 / be
};
// Compute the exponential argument for each layer (Eq. 111 to 113)
// If h < 100km we use h = 100km as recommended in the reference document
final double hTemp = FastMath.max(100.0, h);
final double exp = clipExp(10.0 / (1.0 + FastMath.abs(hTemp - parameters.getHmF2())));
final double[] arguments = new double[3];
arguments[0] = (hTemp - parameters.getHmF2()) / bf2;
arguments[1] = ((hTemp - parameters.getHmF1()) / bf1) * exp;
arguments[2] = ((hTemp - parameters.getHmE()) / be) * exp;
// S coefficients
final double[] s = new double[3];
// Array of corrective terms
final double[] ds = new double[3];
// Layer amplitudes
final double[] amplitudes = parameters.getLayerAmplitudes();
// Fill arrays (Eq. 114 to 118)
for (int i = 0; i < 3; i++) {
if (FastMath.abs(arguments[i]) > 25.0) {
s[i] = 0.0;
ds[i] = 0.0;
} else {
final double expA = clipExp(arguments[i]);
final double opExpA = 1.0 + expA;
s[i] = amplitudes[i] * (expA / (opExpA * opExpA));
ds[i] = ct[i] * ((1.0 - expA) / (1.0 + expA));
}
}
// Electron density
final double aNo = MathArrays.linearCombination(s[0], 1.0, s[1], 1.0, s[2], 1.0);
if (h >= 100) {
return aNo * DENSITY_FACTOR;
} else {
// Chapman parameters (Eq. 119 and 120)
final double bc = 1.0 - 10.0 * (MathArrays.linearCombination(s[0], ds[0], s[1], ds[1], s[2], ds[2]) / aNo);
final double z = 0.1 * (h - 100.0);
// Electron density (Eq. 121)
return aNo * clipExp(1.0 - bc * z - clipExp(-z)) * DENSITY_FACTOR;
}
}
/**
* Computes the electron density of the bottomside.
* @param <T> type of the elements
* @param field field of the elements
* @param h height in km
* @param parameters NeQuick model parameters
* @return the electron density N in m-3
*/
private <T extends RealFieldElement<T>> T bottomElectronDensity(final Field<T> field,
final T h,
final FieldNeQuickParameters<T> parameters) {
// Zero and One
final T zero = field.getZero();
final T one = field.getOne();
// Select the relevant B parameter for the current height (Eq. 109 and 110)
final T be;
if (h.getReal() > parameters.getHmE().getReal()) {
be = parameters.getBETop();
} else {
be = parameters.getBEBot();
}
final T bf1;
if (h.getReal() > parameters.getHmF1().getReal()) {
bf1 = parameters.getB1Top();
} else {
bf1 = parameters.getB1Bot();
}
final T bf2 = parameters.getB2Bot();
// Useful array of constants
final T[] ct = MathArrays.buildArray(field, 3);
ct[0] = bf2.reciprocal();
ct[1] = bf1.reciprocal();
ct[2] = be.reciprocal();
// Compute the exponential argument for each layer (Eq. 111 to 113)
// If h < 100km we use h = 100km as recommended in the reference document
final T hTemp = FastMath.max(zero.add(100.0), h);
final T exp = clipExp(field, FastMath.abs(hTemp.subtract(parameters.getHmF2())).add(1.0).divide(10.0).reciprocal());
final T[] arguments = MathArrays.buildArray(field, 3);
arguments[0] = hTemp.subtract(parameters.getHmF2()).divide(bf2);
arguments[1] = hTemp.subtract(parameters.getHmF1()).divide(bf1).multiply(exp);
arguments[2] = hTemp.subtract(parameters.getHmE()).divide(be).multiply(exp);
// S coefficients
final T[] s = MathArrays.buildArray(field, 3);
// Array of corrective terms
final T[] ds = MathArrays.buildArray(field, 3);
// Layer amplitudes
final T[] amplitudes = parameters.getLayerAmplitudes();
// Fill arrays (Eq. 114 to 118)
for (int i = 0; i < 3; i++) {
if (FastMath.abs(arguments[i]).getReal() > 25.0) {
s[i] = zero;
ds[i] = zero;
} else {
final T expA = clipExp(field, arguments[i]);
final T opExpA = expA.add(1.0);
s[i] = amplitudes[i].multiply(expA.divide(opExpA.multiply(opExpA)));
ds[i] = ct[i].multiply(expA.negate().add(1.0).divide(expA.add(1.0)));
}
}
// Electron density
final T aNo = one.linearCombination(s[0], one, s[1], one, s[2], one);
if (h.getReal() >= 100) {
return aNo.multiply(DENSITY_FACTOR);
} else {
// Chapman parameters (Eq. 119 and 120)
final T bc = s[0].multiply(ds[0]).add(one.linearCombination(s[0], ds[0], s[1], ds[1], s[2], ds[2])).divide(aNo).multiply(10.0).negate().add(1.0);
final T z = h.subtract(100.0).multiply(0.1);
// Electron density (Eq. 121)
return aNo.multiply(clipExp(field, bc.multiply(z).add(clipExp(field, z.negate())).negate().add(1.0))).multiply(DENSITY_FACTOR);
}
}
/**
* Computes the electron density of the topside.
* @param h height in km
* @param parameters NeQuick model parameters
* @return the electron density N in m-3
*/
private double topElectronDensity(final double h, final NeQuickParameters parameters) {
// Constant parameters (Eq. 122 and 123)
final double g = 0.125;
final double r = 100.0;
// Arguments deltaH and z (Eq. 124 and 125)
final double deltaH = h - parameters.getHmF2();
final double z = deltaH / (parameters.getH0() * (1.0 + (r * g * deltaH) / (r * parameters.getH0() + g * deltaH)));
// Exponential (Eq. 126)
final double ee = clipExp(z);
// Electron density (Eq. 127)
if (ee > 1.0e11) {
return (4.0 * parameters.getNmF2() / ee) * DENSITY_FACTOR;
} else {
final double opExpZ = 1.0 + ee;
return ((4.0 * parameters.getNmF2() * ee) / (opExpZ * opExpZ)) * DENSITY_FACTOR;
}
}
/**
* Computes the electron density of the topside.
* @param <T> type of the elements
* @param field field of the elements
* @param h height in km
* @param parameters NeQuick model parameters
* @return the electron density N in m-3
*/
private <T extends RealFieldElement<T>> T topElectronDensity(final Field<T> field,
final T h,
final FieldNeQuickParameters<T> parameters) {
// Constant parameters (Eq. 122 and 123)
final double g = 0.125;
final double r = 100.0;
// Arguments deltaH and z (Eq. 124 and 125)
final T deltaH = h.subtract(parameters.getHmF2());
final T z = deltaH.divide(parameters.getH0().multiply(deltaH.multiply(r).multiply(g).divide(parameters.getH0().multiply(r).add(deltaH.multiply(g))).add(1.0)));
// Exponential (Eq. 126)
final T ee = clipExp(field, z);
// Electron density (Eq. 127)
if (ee.getReal() > 1.0e11) {
return parameters.getNmF2().multiply(4.0).divide(ee).multiply(DENSITY_FACTOR);
} else {
final T opExpZ = ee.add(field.getOne());
return parameters.getNmF2().multiply(4.0).multiply(ee).divide(opExpZ.multiply(opExpZ)).multiply(DENSITY_FACTOR);
}
}
/**
* Lazy loading of CCIR data.
* @param date current date components
*/
private void loadsIfNeeded(final DateComponents date) {
// Current month
final int currentMonth = date.getMonth();
// Check if date have changed or if f2 and fm3 arrays are null
if (currentMonth != month || f2 == null || fm3 == null) {
this.month = currentMonth;
// Read file
final CCIRLoader loader = new CCIRLoader();
loader.loadCCIRCoefficients(date);
// Update arrays
this.f2 = loader.getF2();
this.fm3 = loader.getFm3();
}
}
/**
* A clipped exponential function.
* <p>
* This function, describe in section F.2.12.2 of the reference document, is
* recommanded for the computation of exponential values.
* </p>
* @param power power for exponential function
* @return clipped exponential value
*/
private double clipExp(final double power) {
if (power > 80.0) {
return 5.5406E34;
} else if (power < -80) {
return 1.8049E-35;
} else {
return FastMath.exp(power);
}
}
/**
* A clipped exponential function.
* <p>
* This function, describe in section F.2.12.2 of the reference document, is
* recommanded for the computation of exponential values.
* </p>
* @param <T> type of the elements
* @param field field of the elements
* @param power power for exponential function
* @return clipped exponential value
*/
private <T extends RealFieldElement<T>> T clipExp(final Field<T> field, final T power) {
final T zero = field.getZero();
if (power.getReal() > 80.0) {
return zero.add(5.5406E34);
} else if (power.getReal() < -80) {
return zero.add(1.8049E-35);
} else {
return FastMath.exp(power);
}
}
/** Get a data stream.
* @param name file name of the resource stream
* @return stream
*/
private static InputStream getStream(final String name) {
return NeQuickModel.class.getResourceAsStream(name);
}
/**
* Parser for Modified Dip Latitude (MODIP) grid file.
* <p>
* The MODIP grid allows to estimate MODIP μ [deg] at a given point (φ,λ)
* by interpolation of the relevant values contained in the support file.
* </p> <p>
* The file contains the values of MODIP (expressed in degrees) on a geocentric grid
* from 90°S to 90°N with a 5-degree step in latitude and from 180°W to 180°E with a
* 10-degree in longitude.
* </p>
*/
private static class MODIPLoader {
/** Supported name for MODIP grid. */
private static final String SUPPORTED_NAME = NEQUICK_BASE + "modip.txt";
/** MODIP grid. */
private double[][] grid;
/**
* Build a new instance.
*/
MODIPLoader() {
this.grid = null;
}
/** Returns the MODIP grid array.
* @return the MODIP grid array
*/
public double[][] getMODIPGrid() {
return grid.clone();
}
/**
* Load the data using supported names.
*/
public void loadMODIPGrid() {
try (InputStream in = getStream(SUPPORTED_NAME)) {
loadData(in, SUPPORTED_NAME);
} catch (IOException e) {
throw new OrekitException(OrekitMessages.INTERNAL_ERROR, e);
}
// Throw an exception if MODIP grid was not loaded properly
if (grid == null) {
throw new OrekitException(OrekitMessages.MODIP_GRID_NOT_LOADED, SUPPORTED_NAME);
}
}
/**
* Load data from a stream.
* @param input input stream
* @param name name of the file
* @throws IOException if data can't be read
*/
public void loadData(final InputStream input, final String name)
throws IOException {
// Grid size
final int size = 39;
// Initialize array
final double[][] array = new double[size][size];
// Open stream and parse data
int lineNumber = 0;
String line = null;
try (InputStreamReader isr = new InputStreamReader(input, StandardCharsets.UTF_8);
BufferedReader br = new BufferedReader(isr)) {
for (line = br.readLine(); line != null; line = br.readLine()) {
++lineNumber;
line = line.trim();
// Read grid data
if (line.length() > 0) {
final String[] modip_line = SEPARATOR.split(line);
for (int column = 0; column < modip_line.length; column++) {
array[lineNumber - 1][column] = Double.valueOf(modip_line[column]);
}
}
}
} catch (NumberFormatException nfe) {
throw new OrekitException(OrekitMessages.UNABLE_TO_PARSE_LINE_IN_FILE,
lineNumber, name, line);
}
// Clone parsed grid
grid = array.clone();
}
}
/**
* Parser for CCIR files.
* <p>
* Numerical grid maps which describe the regular variation of the ionosphere.
* They are used to derive other variables such as critical frequencies and transmission factors.
* </p> <p>
* The coefficients correspond to low and high solar activity conditions.
* </p> <p>
* The CCIR file naming convention is ccirXX.asc where each XX means month + 10.
* </p> <p>
* Coefficients are store into tow arrays, F2 and Fm3. F2 coefficients are used for the computation
* of the F2 layer critical frequency. Fm3 for the computation of the F2 layer maximum usable frequency factor.
* The size of these two arrays is fixed and discussed into the section 2.5.3.2
* of the reference document.
* </p>
*/
private static class CCIRLoader {
/** Default supported files name pattern. */
public static final String DEFAULT_SUPPORTED_NAME = "ccir**.asc";
/** Total number of F2 coefficients contained in the file. */
private static final int NUMBER_F2_COEFFICIENTS = 1976;
/** Rows number for F2 and Fm3 arrays. */
private static final int ROWS = 2;
/** Columns number for F2 array. */
private static final int TOTAL_COLUMNS_F2 = 76;
/** Columns number for Fm3 array. */
private static final int TOTAL_COLUMNS_FM3 = 49;
/** Depth of F2 array. */
private static final int DEPTH_F2 = 13;
/** Depth of Fm3 array. */
private static final int DEPTH_FM3 = 9;
/** Regular expression for supported file name. */
private String supportedName;
/** F2 coefficients used for the computation of the F2 layer critical frequency. */
private double[][][] f2Loader;
/** Fm3 coefficients used for the computation of the F2 layer maximum usable frequency factor. */
private double[][][] fm3Loader;
/**
* Build a new instance.
*/
CCIRLoader() {
this.supportedName = DEFAULT_SUPPORTED_NAME;
this.f2Loader = null;
this.fm3Loader = null;
}
/**
* Get the F2 coefficients used for the computation of the F2 layer critical frequency.
* @return the F2 coefficients
*/
public double[][][] getF2() {
return f2Loader.clone();
}
/**
* Get the Fm3 coefficients used for the computation of the F2 layer maximum usable frequency factor.
* @return the F2 coefficients
*/
public double[][][] getFm3() {
return fm3Loader.clone();
}
/** Load the data for a given month.
* @param dateComponents month given but its DateComponents
*/
public void loadCCIRCoefficients(final DateComponents dateComponents) {
// The files are named ccirXX.asc where XX substitute the month of the year + 10
final int currentMonth = dateComponents.getMonth();
this.supportedName = NEQUICK_BASE + String.format("ccir%02d.asc", currentMonth + 10);
try (InputStream in = getStream(supportedName)) {
loadData(in, supportedName);
} catch (IOException e) {
throw new OrekitException(OrekitMessages.INTERNAL_ERROR, e);
}
// Throw an exception if F2 or Fm3 were not loaded properly
if (f2Loader == null || fm3Loader == null) {
throw new OrekitException(OrekitMessages.NEQUICK_F2_FM3_NOT_LOADED, supportedName);
}
}
/**
* Load data from a stream.
* @param input input stream
* @param name name of the file
* @throws IOException if data can't be read
*/
public void loadData(final InputStream input, final String name)
throws IOException {
// Initialize arrays
final double[][][] f2Temp = new double[ROWS][TOTAL_COLUMNS_F2][DEPTH_F2];
final double[][][] fm3Temp = new double[ROWS][TOTAL_COLUMNS_FM3][DEPTH_FM3];
// Placeholders for parsed data
int lineNumber = 0;
int index = 0;
int currentRowF2 = 0;
int currentColumnF2 = 0;
int currentDepthF2 = 0;
int currentRowFm3 = 0;
int currentColumnFm3 = 0;
int currentDepthFm3 = 0;
String line = null;
try (InputStreamReader isr = new InputStreamReader(input, StandardCharsets.UTF_8);
BufferedReader br = new BufferedReader(isr)) {
for (line = br.readLine(); line != null; line = br.readLine()) {
++lineNumber;
line = line.trim();
// Read grid data
if (line.length() > 0) {
final String[] ccir_line = SEPARATOR.split(line);
for (int i = 0; i < ccir_line.length; i++) {
if (index < NUMBER_F2_COEFFICIENTS) {
// Parse F2 coefficients
if (currentDepthF2 >= DEPTH_F2 && currentColumnF2 < (TOTAL_COLUMNS_F2 - 1)) {
currentDepthF2 = 0;
currentColumnF2++;
} else if (currentDepthF2 >= DEPTH_F2 && currentColumnF2 >= (TOTAL_COLUMNS_F2 - 1)) {
currentDepthF2 = 0;
currentColumnF2 = 0;
currentRowF2++;
}
f2Temp[currentRowF2][currentColumnF2][currentDepthF2++] = Double.valueOf(ccir_line[i]);
index++;
} else {
// Parse Fm3 coefficients
if (currentDepthFm3 >= DEPTH_FM3 && currentColumnFm3 < (TOTAL_COLUMNS_FM3 - 1)) {
currentDepthFm3 = 0;
currentColumnFm3++;
} else if (currentDepthFm3 >= DEPTH_FM3 && currentColumnFm3 >= (TOTAL_COLUMNS_FM3 - 1)) {
currentDepthFm3 = 0;
currentColumnFm3 = 0;
currentRowFm3++;
}
fm3Temp[currentRowFm3][currentColumnFm3][currentDepthFm3++] = Double.valueOf(ccir_line[i]);
index++;
}
}
}
}
} catch (NumberFormatException nfe) {
throw new OrekitException(OrekitMessages.UNABLE_TO_PARSE_LINE_IN_FILE,
lineNumber, name, line);
}
f2Loader = f2Temp.clone();
fm3Loader = fm3Temp.clone();
}
}
/**
* Container for ray-perigee parameters.
* By convention, point 1 is at lower height.
*/
private static class Ray {
/** Threshold for ray-perigee parameters computation. */
private static final double THRESHOLD = 1.0e-10;
/** Distance of the first point from the ray perigee [m]. */
private final double s1;
/** Distance of the second point from the ray perigee [m]. */
private final double s2;
/** Ray-perigee radius [m]. */
private final double rp;
/** Ray-perigee latitude [rad]. */
private final double latP;
/** Ray-perigee longitude [rad]. */
private final double lonP;
/** Sine and cosine of ray-perigee latitude. */
private final SinCos scLatP;
/** Sine of azimuth of satellite as seen from ray-perigee. */
private final double sinAzP;
/** Cosine of azimuth of satellite as seen from ray-perigee. */
private final double cosAzP;
/**
* Constructor.
* @param recP receiver position
* @param satP satellite position
*/
Ray(final GeodeticPoint recP, final GeodeticPoint satP) {
// Integration limits in meters (Eq. 140 and 141)
final double r1 = RE + recP.getAltitude();
final double r2 = RE + satP.getAltitude();
// Useful parameters
final double lat1 = recP.getLatitude();
final double lat2 = satP.getLatitude();
final double lon1 = recP.getLongitude();
final double lon2 = satP.getLongitude();
final SinCos scLatSat = FastMath.sinCos(lat2);
final SinCos scLatRec = FastMath.sinCos(lat1);
final SinCos scLon21 = FastMath.sinCos(lon2 - lon1);
// Zenith angle computation (Eq. 153 to 155)
final double cosD = scLatRec.sin() * scLatSat.sin() +
scLatRec.cos() * scLatSat.cos() * scLon21.cos();
final double sinD = FastMath.sqrt(1.0 - cosD * cosD);
final double z = FastMath.atan2(sinD, cosD - (r1 / r2));
// Ray-perigee computation in meters (Eq. 156)
this.rp = r1 * FastMath.sin(z);
// Ray-perigee latitude and longitude
if (FastMath.abs(FastMath.abs(lat1) - 0.5 * FastMath.PI) < THRESHOLD) {
// Ray-perigee latitude (Eq. 157)
if (lat1 < 0) {
this.latP = -z;
} else {
this.latP = z;
}
// Ray-perigee longitude (Eq. 164)
if (z < 0) {
this.lonP = lon2;
} else {
this.lonP = lon2 + FastMath.PI;
}
} else {
// Ray-perigee latitude (Eq. 158 to 163)
final double deltaP = 0.5 * FastMath.PI - z;
final SinCos scDeltaP = FastMath.sinCos(deltaP);
final double sinAz = scLon21.sin() * scLatSat.cos() / sinD;
final double cosAz = (scLatSat.sin() - cosD * scLatRec.sin()) / (sinD * scLatRec.cos());
final double sinLatP = scLatRec.sin() * scDeltaP.cos() - scLatRec.cos() * scDeltaP.sin() * cosAz;
final double cosLatP = FastMath.sqrt(1.0 - sinLatP * sinLatP);
this.latP = FastMath.atan2(sinLatP, cosLatP);
// Ray-perigee longitude (Eq. 165 to 167)
final double sinLonP = -sinAz * scDeltaP.sin() / cosLatP;
final double cosLonP = (scDeltaP.cos() - scLatRec.sin() * sinLatP) / (scLatRec.cos() * cosLatP);
this.lonP = FastMath.atan2(sinLonP, cosLonP) + lon1;
}
// Sine and cosine of ray-perigee latitude
this.scLatP = FastMath.sinCos(latP);
final SinCos scLon = FastMath.sinCos(lon2 - lonP);
// Sine and cosine of azimuth of satellite as seen from ray-perigee
final double psi = greatCircleAngle(scLatSat, scLon);
final SinCos scPsi = FastMath.sinCos(psi);
if (FastMath.abs(FastMath.abs(latP) - 0.5 * FastMath.PI) < THRESHOLD) {
// Eq. 172 and 173
this.sinAzP = 0.0;
if (latP < 0.0) {
this.cosAzP = 1;
} else {
this.cosAzP = -1;
}
} else {
// Eq. 174 and 175
this.sinAzP = scLatSat.cos() * scLon.sin() / scPsi.sin();
this.cosAzP = (scLatSat.sin() - scLatP.sin() * scPsi.cos()) / (scLatP.cos() * scPsi.sin());
}
// Integration en points s1 and s2 in meters (Eq. 176 and 177)
this.s1 = FastMath.sqrt(r1 * r1 - rp * rp);
this.s2 = FastMath.sqrt(r2 * r2 - rp * rp);
}
/**
* Get the distance of the first point from the ray perigee.
* @return s1 in meters
*/
public double getS1() {
return s1;
}
/**
* Get the distance of the second point from the ray perigee.
* @return s2 in meters
*/
public double getS2() {
return s2;
}
/**
* Get the ray-perigee radius.
* @return the ray-perigee radius in meters
*/
public double getRadius() {
return rp;
}
/**
* Get the ray-perigee latitude.
* @return the ray-perigee latitude in radians
*/
public double getLatitude() {
return latP;
}
/**
* Get the ray-perigee longitude.
* @return the ray-perigee longitude in radians
*/
public double getLongitude() {
return lonP;
}
/**
* Get the sine of azimuth of satellite as seen from ray-perigee.
* @return the sine of azimuth
*/
public double getSineAz() {
return sinAzP;
}
/**
* Get the cosine of azimuth of satellite as seen from ray-perigee.
* @return the cosine of azimuth
*/
public double getCosineAz() {
return cosAzP;
}
/**
* Compute the great circle angle from ray-perigee to satellite.
* <p>
* This method used the equations 168 to 171 pf the reference document.
* </p>
* @param scLat sine and cosine of satellite latitude
* @param scLon sine and cosine of satellite longitude minus receiver longitude
* @return the great circle angle in radians
*/
private double greatCircleAngle(final SinCos scLat, final SinCos scLon) {
if (FastMath.abs(FastMath.abs(latP) - 0.5 * FastMath.PI) < THRESHOLD) {
return FastMath.abs(FastMath.asin(scLat.sin()) - latP);
} else {
final double cosPhi = scLatP.sin() * scLat.sin() +
scLatP.cos() * scLat.cos() * scLon.cos();
final double sinPhi = FastMath.sqrt(1.0 - cosPhi * cosPhi);
return FastMath.atan2(sinPhi, cosPhi);
}
}
}
/**
* Container for ray-perigee parameters.
* By convention, point 1 is at lower height.
*/
private static class FieldRay <T extends RealFieldElement<T>> {
/** Threshold for ray-perigee parameters computation. */
private static final double THRESHOLD = 1.0e-10;
/** Distance of the first point from the ray perigee [m]. */
private final T s1;
/** Distance of the second point from the ray perigee [m]. */
private final T s2;
/** Ray-perigee radius [m]. */
private final T rp;
/** Ray-perigee latitude [rad]. */
private final T latP;
/** Ray-perigee longitude [rad]. */
private final T lonP;
/** Sine and cosine of ray-perigee latitude. */
private final FieldSinCos<T> scLatP;
/** Sine of azimuth of satellite as seen from ray-perigee. */
private final T sinAzP;
/** Cosine of azimuth of satellite as seen from ray-perigee. */
private final T cosAzP;
/**
* Constructor.
* @param field field of the elements
* @param recP receiver position
* @param satP satellite position
*/
FieldRay(final Field<T> field, final FieldGeodeticPoint<T> recP, final FieldGeodeticPoint<T> satP) {
// Integration limits in meters (Eq. 140 and 141)
final T r1 = recP.getAltitude().add(RE);
final T r2 = satP.getAltitude().add(RE);
// Useful parameters
final T lat1 = recP.getLatitude();
final T lat2 = satP.getLatitude();
final T lon1 = recP.getLongitude();
final T lon2 = satP.getLongitude();
final FieldSinCos<T> scLatSat = FastMath.sinCos(lat2);
final FieldSinCos<T> scLatRec = FastMath.sinCos(lat1);
// Zenith angle computation (Eq. 153 to 155)
final T cosD = scLatRec.sin().multiply(scLatSat.sin()).
add(scLatRec.cos().multiply(scLatSat.cos()).multiply(FastMath.cos(lon2.subtract(lon1))));
final T sinD = FastMath.sqrt(cosD.multiply(cosD).negate().add(1.0));
final T z = FastMath.atan2(sinD, cosD.subtract(r1.divide(r2)));
// Ray-perigee computation in meters (Eq. 156)
this.rp = r1.multiply(FastMath.sin(z));
// Ray-perigee latitude and longitude
if (FastMath.abs(FastMath.abs(lat1).getReal() - 0.5 * FastMath.PI) < THRESHOLD) {
// Ray-perigee latitude (Eq. 157)
if (lat1.getReal() < 0) {
this.latP = z.negate();
} else {
this.latP = z;
}
// Ray-perigee longitude (Eq. 164)
if (z.getReal() < 0) {
this.lonP = lon2;
} else {
this.lonP = lon2.add(FastMath.PI);
}
} else {
// Ray-perigee latitude (Eq. 158 to 163)
final T deltaP = z.negate().add(0.5 * FastMath.PI);
final FieldSinCos<T> scDeltaP = FastMath.sinCos(deltaP);
final T sinAz = FastMath.sin(lon2.subtract(lon1)).multiply(scLatSat.cos()).divide(sinD);
final T cosAz = scLatSat.sin().subtract(cosD.multiply(scLatRec.sin())).divide(sinD.multiply(scLatRec.cos()));
final T sinLatP = scLatRec.sin().multiply(scDeltaP.cos()).subtract(scLatRec.cos().multiply(scDeltaP.sin()).multiply(cosAz));
final T cosLatP = FastMath.sqrt(sinLatP.multiply(sinLatP).negate().add(1.0));
this.latP = FastMath.atan2(sinLatP, cosLatP);
// Ray-perigee longitude (Eq. 165 to 167)
final T sinLonP = sinAz.negate().multiply(scDeltaP.sin()).divide(cosLatP);
final T cosLonP = scDeltaP.cos().subtract(scLatRec.sin().multiply(sinLatP)).divide(scLatRec.cos().multiply(cosLatP));
this.lonP = FastMath.atan2(sinLonP, cosLonP).add(lon1);
}
// Sine and cosine of ray-perigee latitude
this.scLatP = FastMath.sinCos(latP);
final FieldSinCos<T> scLon = FastMath.sinCos(lon2.subtract(lonP));
// Sine and cosie of azimuth of satellite as seen from ray-perigee
final T psi = greatCircleAngle(scLatSat, scLon);
final FieldSinCos<T> scPsi = FastMath.sinCos(psi);
if (FastMath.abs(FastMath.abs(latP).getReal() - 0.5 * FastMath.PI) < THRESHOLD) {
// Eq. 172 and 173
this.sinAzP = field.getZero();
if (latP.getReal() < 0.0) {
this.cosAzP = field.getOne();
} else {
this.cosAzP = field.getOne().negate();
}
} else {
// Eq. 174 and 175
this.sinAzP = scLatSat.cos().multiply(scLon.sin()).divide(scPsi.sin());
this.cosAzP = scLatSat.sin().subtract(scLatP.sin().multiply(scPsi.cos())).divide(scLatP.cos().multiply(scPsi.sin()));
}
// Integration en points s1 and s2 in meters (Eq. 176 and 177)
this.s1 = FastMath.sqrt(r1.multiply(r1).subtract(rp.multiply(rp)));
this.s2 = FastMath.sqrt(r2.multiply(r2).subtract(rp.multiply(rp)));
}
/**
* Get the distance of the first point from the ray perigee.
* @return s1 in meters
*/
public T getS1() {
return s1;
}
/**
* Get the distance of the second point from the ray perigee.
* @return s2 in meters
*/
public T getS2() {
return s2;
}
/**
* Get the ray-perigee radius.
* @return the ray-perigee radius in meters
*/
public T getRadius() {
return rp;
}
/**
* Get the ray-perigee latitude.
* @return the ray-perigee latitude in radians
*/
public T getLatitude() {
return latP;
}
/**
* Get the ray-perigee longitude.
* @return the ray-perigee longitude in radians
*/
public T getLongitude() {
return lonP;
}
/**
* Get the sine of azimuth of satellite as seen from ray-perigee.
* @return the sine of azimuth
*/
public T getSineAz() {
return sinAzP;
}
/**
* Get the cosine of azimuth of satellite as seen from ray-perigee.
* @return the cosine of azimuth
*/
public T getCosineAz() {
return cosAzP;
}
/**
* Compute the great circle angle from ray-perigee to satellite.
* <p>
* This method used the equations 168 to 171 pf the reference document.
* </p>
* @param scLat sine and cosine of satellite latitude
* @param scLon sine and cosine of satellite longitude minus receiver longitude
* @return the great circle angle in radians
*/
private T greatCircleAngle(final FieldSinCos<T> scLat, final FieldSinCos<T> scLon) {
if (FastMath.abs(FastMath.abs(latP).getReal() - 0.5 * FastMath.PI) < THRESHOLD) {
return FastMath.abs(FastMath.asin(scLat.sin()).subtract(latP));
} else {
final T cosPhi = scLatP.sin().multiply(scLat.sin()).add(
scLatP.cos().multiply(scLat.cos()).multiply(scLon.cos()));
final T sinPhi = FastMath.sqrt(cosPhi.multiply(cosPhi).negate().add(1.0));
return FastMath.atan2(sinPhi, cosPhi);
}
}
}
/** Performs the computation of the coordinates along the integration path. */
private static class Segment {
/** Latitudes [rad]. */
private final double[] latitudes;
/** Longitudes [rad]. */
private final double[] longitudes;
/** Heights [m]. */
private final double[] heights;
/** Integration step [m]. */
private final double deltaN;
/**
* Constructor.
* @param n number of points used for the integration
* @param ray ray-perigee parameters
*/
Segment(final int n, final Ray ray) {
// Integration en points
final double s1 = ray.getS1();
final double s2 = ray.getS2();
// Integration step (Eq. 195)
this.deltaN = (s2 - s1) / n;
// Segments
final double[] s = getSegments(n, s1, s2);
// Useful parameters
final double rp = ray.getRadius();
final SinCos scLatP = FastMath.sinCos(ray.getLatitude());
// Geodetic coordinates
final int size = s.length;
heights = new double[size];
latitudes = new double[size];
longitudes = new double[size];
for (int i = 0; i < size; i++) {
// Heights (Eq. 178)
heights[i] = FastMath.sqrt(s[i] * s[i] + rp * rp) - RE;
// Great circle parameters (Eq. 179 to 181)
final double tanDs = s[i] / rp;
final double cosDs = 1.0 / FastMath.sqrt(1.0 + tanDs * tanDs);
final double sinDs = tanDs * cosDs;
// Latitude (Eq. 182 to 183)
final double sinLatS = scLatP.sin() * cosDs + scLatP.cos() * sinDs * ray.getCosineAz();
final double cosLatS = FastMath.sqrt(1.0 - sinLatS * sinLatS);
latitudes[i] = FastMath.atan2(sinLatS, cosLatS);
// Longitude (Eq. 184 to 187)
final double sinLonS = sinDs * ray.getSineAz() * scLatP.cos();
final double cosLonS = cosDs - scLatP.sin() * sinLatS;
longitudes[i] = FastMath.atan2(sinLonS, cosLonS) + ray.getLongitude();
}
}
/**
* Computes the distance of a point from the ray-perigee.
* @param n number of points used for the integration
* @param s1 lower boundary
* @param s2 upper boundary
* @return the distance of a point from the ray-perigee in km
*/
private double[] getSegments(final int n, final double s1, final double s2) {
// Eq. 196
final double g = 0.5773502691896 * deltaN;
// Eq. 197
final double y = s1 + (deltaN - g) * 0.5;
final double[] segments = new double[2 * n];
int index = 0;
for (int i = 0; i < n; i++) {
// Eq. 198
segments[index] = y + i * deltaN;
index++;
segments[index] = y + i * deltaN + g;
index++;
}
return segments;
}
/**
* Get the latitudes of the coordinates along the integration path.
* @return the latitudes in radians
*/
public double[] getLatitudes() {
return latitudes;
}
/**
* Get the longitudes of the coordinates along the integration path.
* @return the longitudes in radians
*/
public double[] getLongitudes() {
return longitudes;
}
/**
* Get the heights of the coordinates along the integration path.
* @return the heights in m
*/
public double[] getHeights() {
return heights;
}
/**
* Get the integration step.
* @return the integration step in meters
*/
public double getInterval() {
return deltaN;
}
}
/** Performs the computation of the coordinates along the integration path. */
private static class FieldSegment <T extends RealFieldElement<T>> {
/** Latitudes [rad]. */
private final T[] latitudes;
/** Longitudes [rad]. */
private final T[] longitudes;
/** Heights [m]. */
private final T[] heights;
/** Integration step [m]. */
private final T deltaN;
/**
* Constructor.
* @param field field of the elements
* @param n number of points used for the integration
* @param ray ray-perigee parameters
*/
FieldSegment(final Field<T> field, final int n, final FieldRay<T> ray) {
// Integration en points
final T s1 = ray.getS1();
final T s2 = ray.getS2();
// Integration step (Eq. 195)
this.deltaN = s2.subtract(s1).divide(n);
// Segments
final T[] s = getSegments(field, n, s1, s2);
// Useful parameters
final T rp = ray.getRadius();
final FieldSinCos<T> scLatP = FastMath.sinCos(ray.getLatitude());
// Geodetic coordinates
final int size = s.length;
heights = MathArrays.buildArray(field, size);
latitudes = MathArrays.buildArray(field, size);
longitudes = MathArrays.buildArray(field, size);
for (int i = 0; i < size; i++) {
// Heights (Eq. 178)
heights[i] = FastMath.sqrt(s[i].multiply(s[i]).add(rp.multiply(rp))).subtract(RE);
// Great circle parameters (Eq. 179 to 181)
final T tanDs = s[i].divide(rp);
final T cosDs = FastMath.sqrt(tanDs.multiply(tanDs).add(1.0)).reciprocal();
final T sinDs = tanDs.multiply(cosDs);
// Latitude (Eq. 182 to 183)
final T sinLatS = scLatP.sin().multiply(cosDs).add(scLatP.cos().multiply(sinDs).multiply(ray.getCosineAz()));
final T cosLatS = FastMath.sqrt(sinLatS.multiply(sinLatS).negate().add(1.0));
latitudes[i] = FastMath.atan2(sinLatS, cosLatS);
// Longitude (Eq. 184 to 187)
final T sinLonS = sinDs.multiply(ray.getSineAz()).multiply(scLatP.cos());
final T cosLonS = cosDs.subtract(scLatP.sin().multiply(sinLatS));
longitudes[i] = FastMath.atan2(sinLonS, cosLonS).add(ray.getLongitude());
}
}
/**
* Computes the distance of a point from the ray-perigee.
* @param field field of the elements
* @param n number of points used for the integration
* @param s1 lower boundary
* @param s2 upper boundary
* @return the distance of a point from the ray-perigee in km
*/
private T[] getSegments(final Field<T> field, final int n, final T s1, final T s2) {
// Eq. 196
final T g = deltaN.multiply(0.5773502691896);
// Eq. 197
final T y = s1.add(deltaN.subtract(g).multiply(0.5));
final T[] segments = MathArrays.buildArray(field, 2 * n);
int index = 0;
for (int i = 0; i < n; i++) {
// Eq. 198
segments[index] = y.add(deltaN.multiply(i));
index++;
segments[index] = y.add(deltaN.multiply(i)).add(g);
index++;
}
return segments;
}
/**
* Get the latitudes of the coordinates along the integration path.
* @return the latitudes in radians
*/
public T[] getLatitudes() {
return latitudes;
}
/**
* Get the longitudes of the coordinates along the integration path.
* @return the longitudes in radians
*/
public T[] getLongitudes() {
return longitudes;
}
/**
* Get the heights of the coordinates along the integration path.
* @return the heights in m
*/
public T[] getHeights() {
return heights;
}
/**
* Get the integration step.
* @return the integration step in meters
*/
public T getInterval() {
return deltaN;
}
}
}