UnitUtils.java

/**
 * Copyright (c) 2010-2016 by the respective copyright holders.
 *
 * All rights reserved. This program and the accompanying materials
 * are made available under the terms of the Eclipse Public License v1.0
 * which accompanies this distribution, and is available at
 * http://www.eclipse.org/legal/epl-v10.html
 */
package org.openhab.binding.weather.internal.utils;

import org.openhab.binding.weather.internal.common.Unit;

/**
 * Utility class for different unit conversions.
 *
 * @author Gerhard Riegler
 * @since 1.6.0
 */
public class UnitUtils {

    /**
     * Converts celsius to fahrenheit.
     */
    public static Double celsiusToFahrenheit(Double celsius) {
        if (celsius == null) {
            return null;
        }
        return celsius * 1.8 + 32.0;
    }

    /**
     * Converts millimeters to inches.
     */
    public static Double millimetersToInches(Double millimeters) {
        if (millimeters == null) {
            return null;
        }
        return millimeters * 0.0393700787;
    }

    /**
     * Converts kilometers per hour to miles per hour.
     */
    public static Double kmhToMph(Double kmh) {
        if (kmh == null) {
            return null;
        }
        return kmh * 0.621371192;
    }

    /**
     * Converts kilometers per hour to knots.
     */
    public static Double kmhToKnots(Double kmh) {
        if (kmh == null) {
            return null;
        }
        return kmh * 0.539956803;
    }

    /**
     * Converts kilometers per hour to meter per seconds.
     */
    public static Double kmhToMps(Double kmh) {
        if (kmh == null) {
            return null;
        }
        return kmh * 0.277777778;
    }

    /**
     * Converts meter per seconds to kilometers per hour.
     */
    public static Double mpsToKmh(Double mps) {
        if (mps == null) {
            return null;
        }
        return mps / 0.277777778;
    }

    /**
     * Converts kilometers per hour to beaufort.
     */
    public static Double kmhToBeaufort(Double kmh) {
        if (kmh == null) {
            return null;
        }
        return new Double(Math.round(Math.pow(kmh / 3.01, 0.666666666)));
    }

    /**
     * Converts millibar to inches.
     */
    public static Double millibarToInches(Double millibar) {
        if (millibar == null) {
            return null;
        }
        return millibar * 0.0295299830714;
    }

    /**
     * Converts meter to feet.
     */
    public static Double meterToFeet(Double meter) {
        if (meter == null) {
            return null;
        }
        return meter * 3.2808399;
    }

    /**
     * Converts feet to meter.
     */
    public static Double feetToMeter(Double feet) {
        if (feet == null) {
            return null;
        }
        return feet / 3.2808399;
    }

    /**
     * Converts centimeter to millimeter.
     */
    public static Double centimeterToMillimeter(Double centimeter) {
        if (centimeter == null) {
            return null;
        }
        return centimeter * 100;
    }

    /**
     * Calculates the humidex (feels like temperature) from temperature and
     * humidity.
     */
    public static double getHumidex(double temp, int humidity) {
        Double x = 7.5 * temp / (237.7 + temp);
        Double e = 6.112 * Math.pow(10, x) * humidity / 100;
        return temp + (5d / 9d) * (e - 10);
    }

    /**
     * Returns the wind direction based on degree.
     */
    public static String getWindDirection(Integer degree) {
        if (degree < 0 || degree > 360) {
            return null;
        }
        String[] directions = new String[] { "N", "NNE", "NE", "ENE", "E", "ESE", "SE", "SSE", "S", "SSW", "SW", "WSW",
                "W", "WNW", "NW", "NNW" };

        double step = 360.0 / directions.length;
        double b = Math.floor((degree + (step / 2.0)) / step);
        return directions[(int) (b % directions.length)];
    }

    /**
     * Converts a value to the unit configured in the item binding.
     */
    public static Double convertUnit(Double value, Unit unit, String property) {
        if (unit != null) {
            switch (unit) {
                case FAHRENHEIT:
                    return celsiusToFahrenheit(value);
                case MPH:
                    return kmhToMph(value);
                case INCHES:
                    if ("atmosphere.pressure".equals(property)) {
                        return millibarToInches(value);
                    } else if ("precipitation.snow".equals(property)) {
                        return millimetersToInches(centimeterToMillimeter(value));
                    } else {
                        return millimetersToInches(value);
                    }
                case BEAUFORT:
                    return kmhToBeaufort(value);
                case KNOTS:
                    return kmhToKnots(value);
                case MPS:
                    return kmhToMps(value);
            }
        }
        return value;
    }

    /**
     * Computes the sea level pressure depending of observed pressure,
     * temperature and altitude of the observed point
     */
    public static double getSeaLevelPressure(double pressure, double temp, double altitude) {
        double x = 0.0065 * altitude;
        x = (1 - x / (temp + x + 273.15));
        return pressure * Math.pow(x, -5.257);
    }

}