• # How to evaluate azimuth and altitude?

Hi,
I am searching for a simple script which provides the values for azimuth and altitude. Could be a great addon for the sunrise-plugin.

• @ortin Suncalc which is the basis for pimatic-sunrise provides the sun and moon position values at for a given time and location. What kind of calculation are you specifically looking for?

https://www.npmjs.com/package/suncalc#sun-position

``````// get position of the sun (azimuth and altitude) at today's sunrise
var sunrisePos = SunCalc.getPosition(times.sunrise, 51.5, -0.1);

// get sunrise azimuth in degrees
var sunriseAzimuth = sunrisePos.azimuth * 180 / Math.PI;``````

"It always takes longer than you expect, even when you take into account Hofstadter's Law.", Hofstadter's Law

• My idea is to use the calculated values of azimuth and altitude for sun protection. I like to move my shutter only if it is necessary on east and west side. Further from autumn to spring I need to move a shutter in the morning to protect my aquarium from the morning sun. I can handle this more elegant when I check the values by interval.

Perfect would be to have these values as variables directly in pimatic.:D

• @mwittig: Could you be so kind to add these values to the plugin. I would do it, but I can’t. For you it’s just a finger exercise for sure.

• @ortin Is it good enough to provide the values for the current time? In this can imagine to provide these values as variables which will be updated at specified time intervals (interval time can be set via a plugin property, if the interval is set to 0, azimuth and altitude won’t be updated)

"It always takes longer than you expect, even when you take into account Hofstadter's Law.", Hofstadter's Law

• That would be perfect and would be fit excatly to that what I had in mind. Big THX!

• Any news her?

• Okay I tried something and extended the code of suncalc with some lines at the end so that the script returns azimuth and altitude. Not really elegant, but it works for me. From here I have no idea how to get it in the sunrise plugin.

``````/*
SunCalc is a JavaScript library for calculating sun/moon position and light phases.
https://github.com/mourner/suncalc
*/

(function () { 'use strict';

// shortcuts for easier to read formulas

var PI   = Math.PI,
sin  = Math.sin,
cos  = Math.cos,
tan  = Math.tan,
asin = Math.asin,
atan = Math.atan2,
acos = Math.acos,

// sun calculations are based on http://aa.quae.nl/en/reken/zonpositie.html formulas

// date/time constants and conversions

var dayMs = 1000 * 60 * 60 * 24,
J1970 = 2440588,
J2000 = 2451545;

function toJulian(date) { return date.valueOf() / dayMs - 0.5 + J1970; }
function fromJulian(j)  { return new Date((j + 0.5 - J1970) * dayMs); }

// general calculations for position

var e = rad * 23.4397; // obliquity of the Earth

function rightAscension(l, b) { return atan(sin(l) * cos(e) - tan(b) * sin(e), cos(l)); }
function declination(l, b)    { return asin(sin(b) * cos(e) + cos(b) * sin(e) * sin(l)); }

function azimuth(H, phi, dec)  { return atan(sin(H), cos(H) * sin(phi) - tan(dec) * cos(phi)); }
function altitude(H, phi, dec) { return asin(sin(phi) * sin(dec) + cos(phi) * cos(dec) * cos(H)); }

function siderealTime(d, lw) { return rad * (280.16 + 360.9856235 * d) - lw; }

function astroRefraction(h) {
if (h < 0) // the following formula works for positive altitudes only.
h = 0; // if h = -0.08901179 a div/0 would occur.

// formula 16.4 of "Astronomical Algorithms" 2nd edition by Jean Meeus (Willmann-Bell, Richmond) 1998.
// 1.02 / tan(h + 10.26 / (h + 5.10)) h in degrees, result in arc minutes -> converted to rad:
return 0.0002967 / Math.tan(h + 0.00312536 / (h + 0.08901179));
}

// general sun calculations

function solarMeanAnomaly(d) { return rad * (357.5291 + 0.98560028 * d); }

function eclipticLongitude(M) {

var C = rad * (1.9148 * sin(M) + 0.02 * sin(2 * M) + 0.0003 * sin(3 * M)), // equation of center
P = rad * 102.9372; // perihelion of the Earth

return M + C + P + PI;
}

function sunCoords(d) {

var M = solarMeanAnomaly(d),
L = eclipticLongitude(M);

return {
dec: declination(L, 0),
ra: rightAscension(L, 0)
};
}

var SunCalc = {};

// calculates sun position for a given date and latitude/longitude

SunCalc.getPosition = function (date, lat, lng) {

var lw  = rad * -lng,
d   = toDays(date),

c  = sunCoords(d),
H  = siderealTime(d, lw) - c.ra;

return {
azimuth: azimuth(H, phi, c.dec),
altitude: altitude(H, phi, c.dec)
};
};

// sun times configuration (angle, morning name, evening name)

var times = SunCalc.times = [
[-0.833, 'sunrise',       'sunset'      ],
[  -0.3, 'sunriseEnd',    'sunsetStart' ],
[    -6, 'dawn',          'dusk'        ],
[   -12, 'nauticalDawn',  'nauticalDusk'],
[   -18, 'nightEnd',      'night'       ],
[     6, 'goldenHourEnd', 'goldenHour'  ]
];

// adds a custom time to the times config

SunCalc.addTime = function (angle, riseName, setName) {
times.push([angle, riseName, setName]);
};

// calculations for sun times

var J0 = 0.0009;

function julianCycle(d, lw) { return Math.round(d - J0 - lw / (2 * PI)); }

function approxTransit(Ht, lw, n) { return J0 + (Ht + lw) / (2 * PI) + n; }
function solarTransitJ(ds, M, L)  { return J2000 + ds + 0.0053 * sin(M) - 0.0069 * sin(2 * L); }

function hourAngle(h, phi, d) { return acos((sin(h) - sin(phi) * sin(d)) / (cos(phi) * cos(d))); }

// returns set time for the given sun altitude
function getSetJ(h, lw, phi, dec, n, M, L) {

var w = hourAngle(h, phi, dec),
a = approxTransit(w, lw, n);
return solarTransitJ(a, M, L);
}

// calculates sun times for a given date and latitude/longitude

SunCalc.getTimes = function (date, lat, lng) {

var lw = rad * -lng,

d = toDays(date),
n = julianCycle(d, lw),
ds = approxTransit(0, lw, n),

M = solarMeanAnomaly(ds),
L = eclipticLongitude(M),
dec = declination(L, 0),

Jnoon = solarTransitJ(ds, M, L),

i, len, time, Jset, Jrise;

var result = {
solarNoon: fromJulian(Jnoon),
};

for (i = 0, len = times.length; i < len; i += 1) {
time = times[i];

Jset = getSetJ(time[0] * rad, lw, phi, dec, n, M, L);
Jrise = Jnoon - (Jset - Jnoon);

result[time[1]] = fromJulian(Jrise);
result[time[2]] = fromJulian(Jset);
}

return result;
};

// moon calculations, based on http://aa.quae.nl/en/reken/hemelpositie.html formulas

function moonCoords(d) { // geocentric ecliptic coordinates of the moon

var L = rad * (218.316 + 13.176396 * d), // ecliptic longitude
M = rad * (134.963 + 13.064993 * d), // mean anomaly
F = rad * (93.272 + 13.229350 * d),  // mean distance

l  = L + rad * 6.289 * sin(M), // longitude
b  = rad * 5.128 * sin(F),     // latitude
dt = 385001 - 20905 * cos(M);  // distance to the moon in km

return {
ra: rightAscension(l, b),
dec: declination(l, b),
dist: dt
};
}

SunCalc.getMoonPosition = function (date, lat, lng) {

var lw  = rad * -lng,
d   = toDays(date),

c = moonCoords(d),
H = siderealTime(d, lw) - c.ra,
h = altitude(H, phi, c.dec),
// formula 14.1 of "Astronomical Algorithms" 2nd edition by Jean Meeus (Willmann-Bell, Richmond) 1998.
pa = atan(sin(H), tan(phi) * cos(c.dec) - sin(c.dec) * cos(H));

h = h + astroRefraction(h); // altitude correction for refraction

return {
azimuth: azimuth(H, phi, c.dec),
altitude: h,
distance: c.dist,
parallacticAngle: pa
};
};

// calculations for illumination parameters of the moon,
// based on http://idlastro.gsfc.nasa.gov/ftp/pro/astro/mphase.pro formulas and
// Chapter 48 of "Astronomical Algorithms" 2nd edition by Jean Meeus (Willmann-Bell, Richmond) 1998.

SunCalc.getMoonIllumination = function (date) {

var d = toDays(date || new Date()),
s = sunCoords(d),
m = moonCoords(d),

sdist = 149598000, // distance from Earth to Sun in km

phi = acos(sin(s.dec) * sin(m.dec) + cos(s.dec) * cos(m.dec) * cos(s.ra - m.ra)),
inc = atan(sdist * sin(phi), m.dist - sdist * cos(phi)),
angle = atan(cos(s.dec) * sin(s.ra - m.ra), sin(s.dec) * cos(m.dec) -
cos(s.dec) * sin(m.dec) * cos(s.ra - m.ra));

return {
fraction: (1 + cos(inc)) / 2,
phase: 0.5 + 0.5 * inc * (angle < 0 ? -1 : 1) / Math.PI,
angle: angle
};
};

function hoursLater(date, h) {
return new Date(date.valueOf() + h * dayMs / 24);
}

// calculations for moon rise/set times are based on http://www.stargazing.net/kepler/moonrise.html article

SunCalc.getMoonTimes = function (date, lat, lng, inUTC) {
var t = new Date(date);
if (inUTC) t.setUTCHours(0, 0, 0, 0);
else t.setHours(0, 0, 0, 0);

var hc = 0.133 * rad,
h0 = SunCalc.getMoonPosition(t, lat, lng).altitude - hc,
h1, h2, rise, set, a, b, xe, ye, d, roots, x1, x2, dx;

// go in 2-hour chunks, each time seeing if a 3-point quadratic curve crosses zero (which means rise or set)
for (var i = 1; i <= 24; i += 2) {
h1 = SunCalc.getMoonPosition(hoursLater(t, i), lat, lng).altitude - hc;
h2 = SunCalc.getMoonPosition(hoursLater(t, i + 1), lat, lng).altitude - hc;

a = (h0 + h2) / 2 - h1;
b = (h2 - h0) / 2;
xe = -b / (2 * a);
ye = (a * xe + b) * xe + h1;
d = b * b - 4 * a * h1;
roots = 0;

if (d >= 0) {
dx = Math.sqrt(d) / (Math.abs(a) * 2);
x1 = xe - dx;
x2 = xe + dx;
if (Math.abs(x1) <= 1) roots++;
if (Math.abs(x2) <= 1) roots++;
if (x1 < -1) x1 = x2;
}

if (roots === 1) {
if (h0 < 0) rise = i + x1;
else set = i + x1;

} else if (roots === 2) {
rise = i + (ye < 0 ? x2 : x1);
set = i + (ye < 0 ? x1 : x2);
}

if (rise && set) break;

h0 = h2;
}

var result = {};

if (rise) result.rise = hoursLater(t, rise);
if (set) result.set = hoursLater(t, set);

if (!rise && !set) result[ye > 0 ? 'alwaysUp' : 'alwaysDown'] = true;

return result;
};

// export as Node module / AMD module / browser variable
if (typeof exports === 'object' && typeof module !== 'undefined') module.exports = SunCalc;
else if (typeof define === 'function' && define.amd) define(SunCalc);
else window.SunCalc = SunCalc;

// OrTiN
///////////////////////////////////////////////////////////////////////////////////////////////////
var sunrisePos = SunCalc.getPosition(new Date(), yourLatitude, yourLongitude);
var sunriseAzimuth = sunrisePos.azimuth * 180 / Math.PI + 180;
var sunriseAltitude = sunrisePos.altitude * 180 / Math.PI;
console.log("Azimuth  = "+sunriseAzimuth);
console.log("Altitude = "+sunriseAltitude);
///////////////////////////////////////////////////////////////////////////////////////////////////

}());
``````

You must only replace yourLatitude and yourLongitude with your location relevant values.

The script can be started with:
`node suncalc.js`.

It returns:

``````Azimuth  = 318.18168274069535
Altitude = -23.440472955763354
``````

From here I fill two variables in Pimatic via curl patch.

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