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use std::f64::consts::PI;
const MILLISECONDS_PER_DAY : u32 = 1000 * 60 * 60 * 24;
const J1970 : u32 = 2440588;
const J2000 : u32 = 2451545;
const TO_RAD : f64 = PI / 180.0;
const OBLIQUITY_OF_EARTH : f64 = 23.4397 * TO_RAD;
const PERIHELION_OF_EARTH : f64 = 102.9372 * TO_RAD;
#[derive(Debug)]
pub struct Position {
pub azimuth : f64,
pub altitude : f64
}
fn to_julian(unixtime_in_ms: i64) -> f64 {
unixtime_in_ms as f64 /
(MILLISECONDS_PER_DAY as f64) - 0.5 + J1970 as f64
}
#[test]
fn test_to_julian(){
assert_eq!(2457054.5, to_julian(1422748800000));
}
fn to_days(unixtime_in_ms: i64) -> f64 {
to_julian(unixtime_in_ms) - J2000 as f64
}
#[test]
fn test_to_days(){
assert_eq!(5509.5, to_days(1422748800000));
}
fn right_ascension(l:f64, b:f64) -> f64 {
(
l.sin() * OBLIQUITY_OF_EARTH.cos() -
b.tan() * OBLIQUITY_OF_EARTH.sin()
)
.atan2(l.cos())
}
fn declination(l:f64, b:f64) -> f64 {
(
b.sin() * OBLIQUITY_OF_EARTH.cos() +
b.cos() * OBLIQUITY_OF_EARTH.sin() * l.sin()
)
.asin()
}
fn azimuth(h:f64, phi:f64, dec:f64) -> f64 {
h.sin()
.atan2(
h.cos() * phi.sin() -
dec.tan() * phi.cos()
) + PI
}
fn altitude(h:f64, phi:f64, dec:f64) -> f64 {
(
phi.sin() * dec.sin() +
phi.cos() * dec.cos() * h.cos()
)
.asin()
}
fn sidereal_time(d:f64, lw:f64) -> f64 {
(280.16 + 360.9856235 * d).to_radians() - lw
}
fn solar_mean_anomaly(d:f64) -> f64 {
(357.5291 + 0.98560028 * d).to_radians()
}
fn equation_of_center(m:f64) -> f64 {
(1.9148 * (1.0 * m).sin() +
0.02 * (2.0 * m).sin() +
0.0003 * (3.0 * m).sin()
).to_radians()
}
fn ecliptic_longitude(m:f64) -> f64 {
m + equation_of_center(m) + PERIHELION_OF_EARTH + PI
}
pub fn pos(unixtime_in_ms: i64, lat: f64, lon: f64) -> Position {
let lw = -lon.to_radians();
let phi = lat.to_radians();
let d = to_days(unixtime_in_ms);
let m = solar_mean_anomaly(d);
let l = ecliptic_longitude(m);
let dec = declination(l, 0.0);
let ra = right_ascension(l, 0.0);
let h = sidereal_time(d, lw) - ra;
Position {
azimuth : azimuth(h, phi, dec),
altitude : altitude(h, phi, dec)
}
}
#[test]
fn test_pos(){
let date = 1362441600000;
let pos = pos(date, 50.5, 30.5);
assert_eq!(0.6412750628729547, pos.azimuth);
assert_eq!(-0.7000406838781611, pos.altitude);
}