GlobalPressureTemperature2Model.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
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package org.orekit.models.earth.weather;
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.nio.charset.StandardCharsets;
import java.text.ParseException;
import java.util.ArrayList;
import java.util.List;
import java.util.SortedSet;
import java.util.TreeSet;
import java.util.concurrent.atomic.AtomicReference;
import java.util.function.ToDoubleFunction;
import org.hipparchus.analysis.interpolation.BilinearInterpolatingFunction;
import org.hipparchus.util.FastMath;
import org.hipparchus.util.MathUtils;
import org.hipparchus.util.SinCos;
import org.orekit.annotation.DefaultDataContext;
import org.orekit.data.DataContext;
import org.orekit.data.DataLoader;
import org.orekit.data.DataProvidersManager;
import org.orekit.errors.OrekitException;
import org.orekit.errors.OrekitMessages;
import org.orekit.models.earth.Geoid;
import org.orekit.models.earth.troposphere.ViennaOneModel;
import org.orekit.time.AbsoluteDate;
import org.orekit.time.TimeScale;
import org.orekit.utils.Constants;
/** The Global Pressure and Temperature 2 (GPT2) model.
* This model is an empirical model that provides the temperature, the pressure and the water vapor pressure
* of a site depending its latitude and longitude. This model also provides the a<sub>h</sub>
* and a<sub>w</sub> coefficients used for the {@link ViennaOneModel Vienna 1} model.
* <p>
* The requisite coefficients for the computation of the weather parameters are provided by the
* Department of Geodesy and Geoinformation of the Vienna University. They are based on an
* external grid file like "gpt2_1.grd" (1° x 1°) or "gpt2_5.grd" (5° x 5°) available at:
* <a href="http://vmf.geo.tuwien.ac.at/codes/"> link</a>
* </p>
* <p>
* A bilinear interpolation is performed in order to obtained the correct values of the weather parameters.
* </p>
* <p>
* The format is always the same, with and example shown below for the pressure and the temperature.
* <p>
* Example:
* </p>
* <pre>
* % lat lon p:a0 A1 B1 A2 B2 T:a0 A1 B1 A2 B2
* 87.5 2.5 101421 21 409 -217 -122 259.2 -13.2 -6.1 2.6 0.3
* 87.5 7.5 101416 21 411 -213 -120 259.3 -13.1 -6.1 2.6 0.3
* 87.5 12.5 101411 22 413 -209 -118 259.3 -13.1 -6.1 2.6 0.3
* 87.5 17.5 101407 23 415 -205 -116 259.4 -13.0 -6.1 2.6 0.3
* ...
* </pre>
*
* @see "K. Lagler, M. Schindelegger, J. Böhm, H. Krasna, T. Nilsson (2013),
* GPT2: empirical slant delay model for radio space geodetic techniques. Geophys
* Res Lett 40(6):1069–1073. doi:10.1002/grl.50288"
*
* @author Bryan Cazabonne
*
*/
public class GlobalPressureTemperature2Model implements WeatherModel {
/** Default supported files name pattern. */
public static final String DEFAULT_SUPPORTED_NAMES = "gpt2_\\d+.grd";
/** Standard gravity constant [m/s²]. */
private static final double G = Constants.G0_STANDARD_GRAVITY;
/** Ideal gas constant for dry air [J/kg/K]. */
private static final double R = 287.0;
/** Conversion factor from degrees to mill arcseconds. */
private static final int DEG_TO_MAS = 3600000;
/** Shared lazily loaded grid. */
private static final AtomicReference<Grid> SHARED_GRID = new AtomicReference<>(null);
/** South-West grid entry. */
private final GridEntry southWest;
/** South-East grid entry. */
private final GridEntry southEast;
/** North-West grid entry. */
private final GridEntry northWest;
/** North-East grid entry. */
private final GridEntry northEast;
/** The hydrostatic and wet a coefficients loaded. */
private double[] coefficientsA;
/** Geodetic site latitude, radians.*/
private double latitude;
/** Geodetic site longitude, radians.*/
private double longitude;
/** Temperature site, in kelvins. */
private double temperature;
/** Pressure site, in hPa. */
private double pressure;
/** water vapour pressure, in hPa. */
private double e0;
/** Geoid used to compute the undulations. */
private final Geoid geoid;
/** UTC time scale. */
private final TimeScale utc;
/**
* Constructor with supported names given by user. This constructor uses the {@link
* DataContext#getDefault() default data context}.
*
* @param supportedNames supported names
* @param latitude geodetic latitude of the station, in radians
* @param longitude longitude geodetic longitude of the station, in radians
* @param geoid level surface of the gravity potential of a body
* @see #GlobalPressureTemperature2Model(String, double, double, Geoid,
* DataProvidersManager, TimeScale)
*/
@DefaultDataContext
public GlobalPressureTemperature2Model(final String supportedNames, final double latitude,
final double longitude, final Geoid geoid) {
this(supportedNames, latitude, longitude, geoid,
DataContext.getDefault().getDataProvidersManager(),
DataContext.getDefault().getTimeScales().getUTC());
}
/**
* Constructor with supported names and source of GPT2 auxiliary data given by user.
*
* @param supportedNames supported names
* @param latitude geodetic latitude of the station, in radians
* @param longitude longitude geodetic longitude of the station, in radians
* @param geoid level surface of the gravity potential of a body
* @param dataProvidersManager provides access to auxiliary data.
* @param utc UTC time scale.
* @since 10.1
*/
public GlobalPressureTemperature2Model(final String supportedNames,
final double latitude,
final double longitude,
final Geoid geoid,
final DataProvidersManager dataProvidersManager,
final TimeScale utc) {
this.coefficientsA = null;
this.temperature = Double.NaN;
this.pressure = Double.NaN;
this.e0 = Double.NaN;
this.geoid = geoid;
this.latitude = latitude;
this.utc = utc;
// get the lazily loaded shared grid
Grid grid = SHARED_GRID.get();
if (grid == null) {
// this is the first instance we create, we need to load the grid data
final Parser parser = new Parser();
dataProvidersManager.feed(supportedNames, parser);
SHARED_GRID.compareAndSet(null, parser.grid);
grid = parser.grid;
}
// Normalize longitude according to the grid
this.longitude = MathUtils.normalizeAngle(longitude, grid.entries[0][0].longitude + FastMath.PI);
final int southIndex = grid.getSouthIndex(this.latitude);
final int westIndex = grid.getWestIndex(this.longitude);
this.southWest = grid.entries[southIndex ][westIndex ];
this.southEast = grid.entries[southIndex ][westIndex + 1];
this.northWest = grid.entries[southIndex + 1][westIndex ];
this.northEast = grid.entries[southIndex + 1][westIndex + 1];
}
/**
* Constructor with default supported names. This constructor uses the {@link
* DataContext#getDefault() default data context}.
*
* @param latitude geodetic latitude of the station, in radians
* @param longitude geodetic latitude of the station, in radians
* @param geoid level surface of the gravity potential of a body
* @see #GlobalPressureTemperature2Model(String, double, double, Geoid,
* DataProvidersManager, TimeScale)
*/
@DefaultDataContext
public GlobalPressureTemperature2Model(final double latitude, final double longitude, final Geoid geoid) {
this(DEFAULT_SUPPORTED_NAMES, latitude, longitude, geoid);
}
/** Returns the a coefficients array.
* <ul>
* <li>double[0] = a<sub>h</sub>
* <li>double[1] = a<sub>w</sub>
* </ul>
* @return the a coefficients array
*/
public double[] getA() {
return coefficientsA.clone();
}
/** Returns the temperature at the station [K].
* @return the temperature at the station [K]
*/
public double getTemperature() {
return temperature;
}
/** Returns the pressure at the station [hPa].
* @return the pressure at the station [hPa]
*/
public double getPressure() {
return pressure;
}
/** Returns the water vapor pressure at the station [hPa].
* @return the water vapor pressure at the station [hPa]
*/
public double getWaterVaporPressure() {
return e0;
}
@Override
public void weatherParameters(final double stationHeight, final AbsoluteDate currentDate) {
final int dayOfYear = currentDate.getComponents(utc).getDate().getDayOfYear();
// ah and aw coefficients
coefficientsA = new double[] {
interpolate(e -> evaluate(dayOfYear, e.ah)) * 0.001,
interpolate(e -> evaluate(dayOfYear, e.aw)) * 0.001
};
// Corrected height (can be negative)
final double undu = geoid.getUndulation(latitude, longitude, currentDate);
final double correctedheight = stationHeight - undu - interpolate(e -> e.hS);
// Temperature gradient [K/m]
final double dTdH = interpolate(e -> evaluate(dayOfYear, e.dT)) * 0.001;
// Specific humidity
final double qv = interpolate(e -> evaluate(dayOfYear, e.qv0)) * 0.001;
// For the computation of the temperature and the pressure, we use
// the standard ICAO atmosphere formulas.
// Temperature [K]
final double t0 = interpolate(e -> evaluate(dayOfYear, e.temperature0));
this.temperature = t0 + dTdH * correctedheight;
// Pressure [hPa]
final double p0 = interpolate(e -> evaluate(dayOfYear, e.pressure0));
final double exponent = G / (dTdH * R);
this.pressure = p0 * FastMath.pow(1 - (dTdH / t0) * correctedheight, exponent) * 0.01;
// Water vapor pressure [hPa]
this.e0 = qv * pressure / (0.622 + 0.378 * qv);
}
/** Interpolate a grid function.
* @param gridGetter getter for the grid function
* @return interpolated function"
*/
private double interpolate(final ToDoubleFunction<GridEntry> gridGetter) {
// cell surrounding the point
final double[] xVal = new double[] {
southWest.longitude, southEast.longitude
};
final double[] yVal = new double[] {
southWest.latitude, northWest.latitude
};
// evaluate grid points at specified day
final double[][] fval = new double[][] {
{
gridGetter.applyAsDouble(southWest),
gridGetter.applyAsDouble(northWest)
}, {
gridGetter.applyAsDouble(southEast),
gridGetter.applyAsDouble(northEast)
}
};
// perform interpolation in the grid
return new BilinearInterpolatingFunction(xVal, yVal, fval).value(longitude, latitude);
}
/** Evaluate a model for some day.
* @param dayOfYear day to evaluate
* @param model model array
* @return model value at specified day
*/
private double evaluate(final int dayOfYear, final double[] model) {
final double coef = (dayOfYear / 365.25) * 2 * FastMath.PI;
final SinCos sc1 = FastMath.sinCos(coef);
final SinCos sc2 = FastMath.sinCos(2.0 * coef);
return model[0] +
model[1] * sc1.cos() + model[2] * sc1.sin() +
model[3] * sc2.cos() + model[4] * sc2.sin();
}
/** Parser for GPT2 grid files. */
private static class Parser implements DataLoader {
/** Grid entries. */
private Grid grid;
@Override
public boolean stillAcceptsData() {
return grid == null;
}
@Override
public void loadData(final InputStream input, final String name)
throws IOException, ParseException {
final SortedSet<Integer> latSample = new TreeSet<>();
final SortedSet<Integer> lonSample = new TreeSet<>();
final List<GridEntry> entries = new ArrayList<>();
// 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)) {
final String splitter = "\\s+";
for (line = br.readLine(); line != null; line = br.readLine()) {
++lineNumber;
line = line.trim();
// read grid data
if (line.length() > 0 && !line.startsWith("%")) {
final GridEntry entry = new GridEntry(line.split(splitter));
latSample.add(entry.latKey);
lonSample.add(entry.lonKey);
entries.add(entry);
}
}
} catch (NumberFormatException nfe) {
throw new OrekitException(OrekitMessages.UNABLE_TO_PARSE_LINE_IN_FILE,
lineNumber, name, line);
}
// organize entries in a grid that wraps arouns Earth in longitude
grid = new Grid(latSample, lonSample, entries, name);
}
}
/** Container for complete grid. */
private static class Grid {
/** Latitude sample. */
private final SortedSet<Integer> latitudeSample;
/** Longitude sample. */
private final SortedSet<Integer> longitudeSample;
/** Grid entries. */
private final GridEntry[][] entries;
/** Simple constructor.
* @param latitudeSample latitude sample
* @param longitudeSample longitude sample
* @param loadedEntries loaded entries, organized as a simple list
* @param name file name
*/
Grid(final SortedSet<Integer> latitudeSample, final SortedSet<Integer> longitudeSample,
final List<GridEntry> loadedEntries, final String name) {
final int nA = latitudeSample.size();
final int nO = longitudeSample.size() + 1; // we add one here for wrapping the grid
this.entries = new GridEntry[nA][nO];
this.latitudeSample = latitudeSample;
this.longitudeSample = longitudeSample;
// organize entries in the regular grid
for (final GridEntry entry : loadedEntries) {
final int latitudeIndex = latitudeSample.headSet(entry.latKey + 1).size() - 1;
final int longitudeIndex = longitudeSample.headSet(entry.lonKey + 1).size() - 1;
entries[latitudeIndex][longitudeIndex] = entry;
}
// finalize the grid
for (final GridEntry[] row : entries) {
// check for missing entries
for (int longitudeIndex = 0; longitudeIndex < nO - 1; ++longitudeIndex) {
if (row[longitudeIndex] == null) {
throw new OrekitException(OrekitMessages.IRREGULAR_OR_INCOMPLETE_GRID, name);
}
}
// wrap the grid around the Earth in longitude
row[nO - 1] = new GridEntry(row[0].latitude, row[0].latKey,
row[0].longitude + 2 * FastMath.PI,
row[0].lonKey + DEG_TO_MAS * 360,
row[0].hS, row[0].pressure0, row[0].temperature0,
row[0].qv0, row[0].dT, row[0].ah, row[0].aw);
}
}
/** Get index of South entries in the grid.
* @param latitude latitude to locate (radians)
* @return index of South entries in the grid
*/
public int getSouthIndex(final double latitude) {
final int latKey = (int) FastMath.rint(FastMath.toDegrees(latitude) * DEG_TO_MAS);
final int index = latitudeSample.headSet(latKey + 1).size() - 1;
// make sure we have at least one point remaining on North by clipping to size - 2
return FastMath.min(index, latitudeSample.size() - 2);
}
/** Get index of West entries in the grid.
* @param longitude longitude to locate (radians)
* @return index of West entries in the grid
*/
public int getWestIndex(final double longitude) {
final int lonKey = (int) FastMath.rint(FastMath.toDegrees(longitude) * DEG_TO_MAS);
final int index = longitudeSample.headSet(lonKey + 1).size() - 1;
// we don't do clipping in longitude because we have added a row to wrap around the Earth
return index;
}
}
/** Container for grid entries. */
private static class GridEntry {
/** Latitude (radian). */
private final double latitude;
/** Latitude key (mas). */
private final int latKey;
/** Longitude (radian). */
private final double longitude;
/** Longitude key (mas). */
private final int lonKey;
/** Height correction. */
private final double hS;
/** Pressure model. */
private final double[] pressure0;
/** Temperature model. */
private final double[] temperature0;
/** Specific humidity model. */
private final double[] qv0;
/** Temperature gradient model. */
private final double[] dT;
/** ah coefficient model. */
private final double[] ah;
/** aw coefficient model. */
private final double[] aw;
/** Build an entry from a parsed line.
* @param fields line fields
*/
GridEntry(final String[] fields) {
final double latDegree = Double.parseDouble(fields[0]);
final double lonDegree = Double.parseDouble(fields[1]);
latitude = FastMath.toRadians(latDegree);
longitude = FastMath.toRadians(lonDegree);
latKey = (int) FastMath.rint(latDegree * DEG_TO_MAS);
lonKey = (int) FastMath.rint(lonDegree * DEG_TO_MAS);
hS = Double.parseDouble(fields[23]);
pressure0 = createModel(fields, 2);
temperature0 = createModel(fields, 7);
qv0 = createModel(fields, 12);
dT = createModel(fields, 17);
ah = createModel(fields, 24);
aw = createModel(fields, 29);
}
/** Build an entry from its components.
* @param latitude latitude (radian)
* @param latKey latitude key (mas)
* @param longitude longitude (radian)
* @param lonKey longitude key (mas)
* @param hS height correction
* @param pressure0 pressure model
* @param temperature0 temperature model
* @param qv0 specific humidity model
* @param dT temperature gradient model
* @param ah ah coefficient model
* @param aw aw coefficient model
*/
GridEntry(final double latitude, final int latKey, final double longitude, final int lonKey,
final double hS, final double[] pressure0, final double[] temperature0,
final double[] qv0, final double[] dT, final double[] ah, final double[] aw) {
this.latitude = latitude;
this.latKey = latKey;
this.longitude = longitude;
this.lonKey = lonKey;
this.hS = hS;
this.pressure0 = pressure0.clone();
this.temperature0 = temperature0.clone();
this.qv0 = qv0.clone();
this.dT = dT.clone();
this.ah = ah.clone();
this.aw = aw.clone();
}
/** Create a time model array.
* @param fields line fields
* @param first index of the first component of the model
* @return time model array
*/
private double[] createModel(final String[] fields, final int first) {
return new double[] {
Double.parseDouble(fields[first ]),
Double.parseDouble(fields[first + 1]),
Double.parseDouble(fields[first + 2]),
Double.parseDouble(fields[first + 3]),
Double.parseDouble(fields[first + 4])
};
}
}
}