martinc / daylight

A swift package that provides NOAA astronomical algorithms for sunrise and sunset times

daylight

A swift package that provides NOAA astrological algorithms for sunrise and sunset times

A port of the go library astrotime

You can either use the interface with a Day struct containing the calendar date of interest, or use the interface of a Date object.

Note that using the Date object's interface will use the calendar date at the timezone of the Location.

The SolarEvent enum is used to specify the event of interest.

Example

let julyFirst = Day(year: 2015, month: 7, day: 1)
let newyork = Location(tz: TimeZone(identifier: "America/New_York")!,
                       coords: Coords(latitude: 40.642, longitude: -74.017))
let sunrise = julyFirst.timeOf(.sunrise, at: newyork)

//Format it to display in location's timezone
let dateFormatter = DateFormatter()
dateFormatter.timeZone = newyork.tz
dateFormatter.dateStyle = .long
dateFormatter.timeStyle = .long
print("Sunrise: \(dateFormatter.string(from: sunrise))")

Interface

public enum SolarEvent {
    case sunrise
    case noon
    case sunset
    case civilDawn
    case civilDusk
    case nauticalDawn
    case nauticalDusk
    case astronomicalDawn
    case astronomicalDusk
}

public struct Location {
    public let tz: TimeZone
    public let coords: CLLocationCoordinate2D
}

public struct Day {
    public let year: Int, month: Int, day: Int
    public func timeOf(_ solarEvent: SolarEvent, at location: Location) -> Date
}

public extension Date {
    public func timeOf(_ solarEvent: SolarEvent, at location: Location) -> Date
    public func timeOfNext(_ solarEvent: SolarEvent, at location: Location) -> Date
}

Running tests

In addition to with XCode, you can run the test suite via the command-line with the following command:

swift test

daylight's Issues

Enhancement - Location is in Daylight

I stumbled across this looking for a map overlay for MapKit to show daylight/night over map of the world. I am glad to see a solid foundation in this project.

Here's an enhancement I'd like to see:

Given a longitude and latitude, at the current time, is that location in daylight or darkness.

[User could choose what they consider daylight from the SolarEvent enum. It would be great if we did not have to worry about time zone and just a location on earth at the current time.]

So maybe something like:

let currentLocation = CLLocationCoordinate2D(latitude: 40.642, longitude: -74.017)
let inDaylight: Bool = currentLocation.inDaylight(usingDawn: .civilDawn, andDusk: .civilDusk)

I'll be playing around with what you have. Beats starting from NASA's codeI've seen since this is already migrated to Swift.

Daylight framework crashes app if the location is inside polar ring.

Locations inside polar ring, will have polar days (sun never sets) and polar nights (sun never rises).

private func hourAngleOfSunrise(latitude: Float64, solarDeclination: Float64, solarElevation: Float64) throws -> Float64

This function return NAN when sun never rises or sun never sets.

I have made a work around to solve this problem by throw an error from there (and re-throw it along the method chain). I don't have a better solution to handle this situation, so I hope you can look into it.

The workaround I've made was in commit eca031c.

Thank you.