djben/spacetime

Astronomical space coordinate and time conversion. Calculate Julian day, local sidereal time and ecliptic obliquity with great precision.

SpaceTime

Overview

• Conversion among equatorial coordinate (right ascension and declination), horizontal coordinate (azimuth and altitude), ecliptic coordinate (longitude and latitude) and their corresponding Cartesian equivalents.
• Calculate Julian Day and Local sidereal time.
• High precision calculation of the obliquity of ecliptic good to 0″.04 / 1000 years over 10000 years.
• Matrix / Quaternion transformation from celestial coordinate system to local tangent plane. Supports North-East-Down coordinate from earth-centered, earth-fixed coordinate system for any given longitude, latitude and timestamp.

Demo

You can find a demo project under SpaceTimeDemo directory. It showcases several useful scenarios.

Installation

Carthage

github "DJBen/SpaceTime" ~> 0.4.0

Usage

Equatorial to horizontal coordinate:

// Supply observer location and timestamp
let locTime = ObserverLocationTime(location: location, timestamp: JulianDay.now)
let vegaCoord = EquatorialCoordinate(rightAscension: radians(hours: 18, minutes: 36, seconds: 56.33635), declination: radians(degrees: 38, minutes: 47, seconds: 1.2802), distance: 1)
// Azimuth and altitude of Vega
let vegaAziAlt = HorizontalCoordinate.init(equatorialCoordinate: vegaCoord, observerInfo: locTime)

Ecliptic coordinate of Pollux at standard equinox of J2000.0.

let ra = DegreeAngle(116.328942)
let dec = DegreeAngle(28.026183)
let eclipticCoord = EclipticCoordinate(longitude: ra, latitude: dec, distance: 1, julianDay: .J2000)
eclipticCoord.longitude.wrappedValue // 113.21563
eclipticCoord.latitude.wrappedValue // 6.68417

Greenwich Mean Sidereal Time:

SiderealTime.init(julianDay: JulianDay.now)

Local Apparent Sidereal Time:

// Get location from GPS or hard code
let locTime = ObserverLocationTime(location: location, timestamp: JulianDay.now)
let localSidTime = SiderealTime.init(observerLocationTime: locTime)

More use cases can be found in the source and test cases.

spacetime's Issues

enhancement - scenekit / arkit helpers to display planet locations based off user location / JD

I'm looking to display planets based off user location.

Perhaps we can cherry pick some of the code / logic from @calda .
https://github.com/HTN-2017/AR-Planes

https://www.youtube.com/watch?v=dnYHQ-7wlag
screen shot 2018-03-09 at 11 18 31 am

I'm looking for something as trivial as
here's my date / time / coordinate - where is the corresponding planet pluto / mars / etc.
https://github.com/HTN-2017/AR-Planes/blob/master/AR%20Planes/Model/Flight.swift

struct Flight {

// MARK: - Properties

let icao: String
let callsign: String
let longitude: Double
let latitude: Double
let altitude: Double
let noseHeading: Double
let groundVelocity: Double
let verticalVelocity: Double

var location: CLLocation {
    let coordinate = CLLocationCoordinate2D(latitude: latitude, longitude: longitude)
    
    //note: CLLocation also accepts heading and speed, could be useful?
    return CLLocation(
        coordinate: coordinate,
        altitude: altitude,
        horizontalAccuracy: 1,
        verticalAccuracy: 1,
        timestamp: Date())
}

func sceneKitCoordinate(relativeTo userLocation: CLLocation) -> SCNVector3 {
let distance = location.distance(from: userLocation)
let heading = userLocation.coordinate.getHeading(toPoint: location.coordinate)
let headingRadians = heading * (.pi/180)

    let distanceScale: Double = 1/140
    let eastWestOffset = distance * sin(headingRadians) * distanceScale
    let northSouthOffset = distance * cos(headingRadians)  * distanceScale
    
    let altitudeScale: Double = 1/140 //1/20
    let upDownOffset = altitude * altitudeScale
    
    //in .gravityAndHeading, (1, 1, 1) is (east, up, south)
    return SCNVector3(eastWestOffset, upDownOffset, -northSouthOffset)
}