| /* |
| * Copyright (C) 2010 The Android Open Source Project |
| * |
| * Licensed 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 com.android.server; |
| |
| import android.text.format.DateUtils; |
| |
| /** @hide */ |
| public class TwilightCalculator { |
| |
| /** Value of {@link #mState} if it is currently day */ |
| public static final int DAY = 0; |
| |
| /** Value of {@link #mState} if it is currently night */ |
| public static final int NIGHT = 1; |
| |
| private static final float DEGREES_TO_RADIANS = (float) (Math.PI / 180.0f); |
| |
| // element for calculating solar transit. |
| private static final float J0 = 0.0009f; |
| |
| // correction for civil twilight |
| private static final float ALTIDUTE_CORRECTION_CIVIL_TWILIGHT = -0.104719755f; |
| |
| // coefficients for calculating Equation of Center. |
| private static final float C1 = 0.0334196f; |
| private static final float C2 = 0.000349066f; |
| private static final float C3 = 0.000005236f; |
| |
| private static final float OBLIQUITY = 0.40927971f; |
| |
| // Java time on Jan 1, 2000 12:00 UTC. |
| private static final long UTC_2000 = 946728000000L; |
| |
| /** |
| * Time of sunset (civil twilight) in milliseconds or -1 in the case the day |
| * or night never ends. |
| */ |
| public long mSunset; |
| |
| /** |
| * Time of sunrise (civil twilight) in milliseconds or -1 in the case the |
| * day or night never ends. |
| */ |
| public long mSunrise; |
| |
| /** Current state */ |
| public int mState; |
| |
| /** |
| * calculates the civil twilight bases on time and geo-coordinates. |
| * |
| * @param time time in milliseconds. |
| * @param latiude latitude in degrees. |
| * @param longitude latitude in degrees. |
| */ |
| public void calculateTwilight(long time, double latiude, double longitude) { |
| final float daysSince2000 = (float) (time - UTC_2000) / DateUtils.DAY_IN_MILLIS; |
| |
| // mean anomaly |
| final float meanAnomaly = 6.240059968f + daysSince2000 * 0.01720197f; |
| |
| // true anomaly |
| final double trueAnomaly = meanAnomaly + C1 * Math.sin(meanAnomaly) + C2 |
| * Math.sin(2 * meanAnomaly) + C3 * Math.sin(3 * meanAnomaly); |
| |
| // ecliptic longitude |
| final double solarLng = trueAnomaly + 1.796593063d + Math.PI; |
| |
| // solar transit in days since 2000 |
| final double arcLongitude = -longitude / 360; |
| float n = Math.round(daysSince2000 - J0 - arcLongitude); |
| double solarTransitJ2000 = n + J0 + arcLongitude + 0.0053d * Math.sin(meanAnomaly) |
| + -0.0069d * Math.sin(2 * solarLng); |
| |
| // declination of sun |
| double solarDec = Math.asin(Math.sin(solarLng) * Math.sin(OBLIQUITY)); |
| |
| final double latRad = latiude * DEGREES_TO_RADIANS; |
| |
| double cosHourAngle = (Math.sin(ALTIDUTE_CORRECTION_CIVIL_TWILIGHT) - Math.sin(latRad) |
| * Math.sin(solarDec)) / (Math.cos(latRad) * Math.cos(solarDec)); |
| // The day or night never ends for the given date and location, if this value is out of |
| // range. |
| if (cosHourAngle >= 1) { |
| mState = NIGHT; |
| mSunset = -1; |
| mSunrise = -1; |
| return; |
| } else if (cosHourAngle <= -1) { |
| mState = DAY; |
| mSunset = -1; |
| mSunrise = -1; |
| return; |
| } |
| |
| float hourAngle = (float) (Math.acos(cosHourAngle) / (2 * Math.PI)); |
| |
| mSunset = Math.round((solarTransitJ2000 + hourAngle) * DateUtils.DAY_IN_MILLIS) + UTC_2000; |
| mSunrise = Math.round((solarTransitJ2000 - hourAngle) * DateUtils.DAY_IN_MILLIS) + UTC_2000; |
| |
| if (mSunrise < time && mSunset > time) { |
| mState = DAY; |
| } else { |
| mState = NIGHT; |
| } |
| } |
| |
| } |