我正在开发一款具有夜间自动进入暗夜模式功能的应用。该应用程序询问用户位置并使用this algorithm确定日出/日落时数（以世界时间计）。
唯一不明确的步骤是从UT转换为本地时间，因为算法中没有解释这一点。假设我的日出时间是8.5（早上8点30分）。如何将其转换为用户的当地时间以检查是白天还是晚上？或者等效地，我如何将用户的本地时间转换为UT以便能够比较它们？
到目前为止，我已尝试使用NSCalendar获取当前日期的NSDateComponents（NSDate()）。其中一个组件是NSTimeZone?，我可以从secondsFromGMT获取let dateComponents = NSCalendar.currentCalendar().components([.TimeZone], fromDate: NSDate())
let localOffset = Double(dateComponents.timeZone?.secondsFromGMT ?? 0)/3600
。像这样：
localOffset其中dateComponents.timeZone == nil应该是UT的时间差（以小时为单位）（即如果我是正确的GMT）到当地时间，如果localOffset则默认为0（我不知道在哪种情况下）这可能发生）。问题是我现在得到的daylightSavingTime比未来的6个月（当夏令时不同于我现在在西班牙的时候）。这是否意味着我需要将属性daylightSavingTimeOffset和/或secondsFromGMT与secondsFromGMT一起使用？ import Foundation
import CoreLocation
enum SunriseSunsetZenith: Double {
case Official = 90.83
case Civil = 96
case Nautical = 102
case Astronomical = 108
}
func sunriseSunsetHoursForLocation(coordinate: CLLocationCoordinate2D, atDate date: NSDate = NSDate(), zenith: SunriseSunsetZenith = .Civil) -> (sunrise: Double, sunset: Double) {
// Initial values (will be changed later)
var sunriseTime = 7.5
var sunsetTime = 19.5
// Get the longitude and latitude
let latitude = coordinate.latitude
let longitude = coordinate.longitude
// Get the day, month, year and local offset
let dateComponents = NSCalendar.currentCalendar().components([.Day, .Month, .Year, .TimeZone], fromDate: date)
let day = Double(dateComponents.day)
let month = Double(dateComponents.month)
let year = Double(dateComponents.year)
let localOffset = Double(dateComponents.timeZone?.daylightSavingTimeOffset ?? 0)/3600
// Calculate the day of the year
let N1 = floor(275*month/9)
let N2 = floor((month + 9)/12)
let N3 = 1 + floor((year - 4*floor(year/4) + 2)/3)
let dayOfYear = N1 - N2*N3 + day - 30
for i in 0...1 {
// Convert the longitude to hour value and calculate an approximate time
let longitudeHour = longitude/15
let t = dayOfYear + ((i == 0 ? 6.0 : 18.0) - longitudeHour)/24
// Calculate the Sun's mean anomaly
let M = 0.9856*t - 3.289
// Calculate the Sun's true longitude
var L = M + 1.916*sind(M) + 0.020*sind(2*M) + 282.634
L %= 360
// Calculate the Sun's right ascension
var RA = atand(0.91764 * tand(L))
RA %= 360
let Lquadrant = (floor(L/90))*90
let RAquadrant = (floor(RA/90))*90
RA += Lquadrant - RAquadrant
RA /= 15
// Calculate the Sun's declination
let sinDec = 0.39782*sind(L)
let cosDec = cosd(asind(sinDec))
// Calculate the Sun's local hour angle
let cosH = (cosd(zenith.rawValue) - sinDec*sind(latitude))/(cosDec*cosd(latitude))
if cosH > 1 { // The sun never rises on this location (on the specified date)
sunriseTime = Double.infinity
sunsetTime = -Double.infinity
} else if cosH < -1 { // The sun never sets on this location (on the specified date)
sunriseTime = -Double.infinity
sunsetTime = Double.infinity
} else {
// Finish calculating H and convert into hours
var H = ( i == 0 ? 360.0 : 0.0 ) + ( i == 0 ? -1.0 : 1.0 )*acosd(cosH)
H /= 15
// Calculate local mean time of rising/setting
let T = H + RA - 0.06571*t - 6.622
// Adjust back to UTC
let UT = T - longitudeHour
// Convert UT value to local time zone of latitude/longitude
let localT = UT + localOffset
if i == 0 { // Add 24 and modulo 24 to be sure that the results is between 0..<24
sunriseTime = (localT + 24)%24
} else {
sunsetTime = (localT + 24)%24
}
}
}
return (sunriseTime, sunsetTime)
}
func sind(valueInDegrees: Double) -> Double {
return sin(valueInDegrees*M_PI/180)
}
func cosd(valueInDegrees: Double) -> Double {
return cos(valueInDegrees*M_PI/180)
}
func tand(valueInDegrees: Double) -> Double {
return tan(valueInDegrees*M_PI/180)
}
func asind(valueInRadians: Double) -> Double {
return asin(valueInRadians)*180/M_PI
}
func acosd(valueInRadians: Double) -> Double {
return acos(valueInRadians)*180/M_PI
}
func atand(valueInRadians: Double) -> Double {
return atan(valueInRadians)*180/M_PI
}
本身不会解释这个问题吗？
当我从算法中读取结果时，事情变得更加混乱。太阳下山时间（当地时间）正好是谷歌提供的时间，但是太阳升起的时间比Google说的要早一个小时（对于我的位置和日期）。我与你分享整个Swift算法的实现，希望它可以帮助别人发现我做错了什么。
let latitude = ...
let longitude = ...
let coordinate = CLLocationCoordinate2D(latitude: latitude, longitude: longitude)
let (sunriseHour, sunsetHour) = sunriseSunsetHoursForLocation(coordinate)
let componetns = NSCalendar.currentCalendar().components([.Hour, .Minute], fromDate: NSDate())
let currentHour = Double(componetns.hour) + Double(componetns.minute)/60
let isNight = currentHour < sunriseHour || currentHour > sunsetHour
这是我使用该功能确定是否是夜晚的方法：
$.onFileUpload(event);答案 0 :(得分：1)
我不确定为什么你的代码得到偏移不起作用（我得到了相同的结果）。但是有一个更简单的解决方案可行。只需使用secondsFromGMTForDate询问当地时区即可。如果日期相隔六个月，我会得到不同的结果：
let now = NSDate()
let future = NSCalendar.currentCalendar().dateByAddingUnit(NSCalendarUnit.Month, value: 6, toDate: now, options: NSCalendarOptions(rawValue: 0))!
let nowOffset = NSTimeZone.localTimeZone().secondsFromGMTForDate(now)/3600
let futureOffset = NSTimeZone.localTimeZone().secondsFromGMTForDate(future)/3600