BangleApps/apps/planetarium/planetarium.app.js

/*
 * Degrees to radians
 */
function toRadians(degrees)
{
    return Math.PI * degrees / 180;
}

/*
 * Julian day number
 * Assumes a proleptic gregorian calendar where the year 1 is preceded by the
 * year 0.
 */
function toJulianDay(year, month, day, hours, minutes, seconds)
{
    day += hours / 24 + minutes / 1440 + seconds / 86400;
    
    if(month <= 2)
    {
        year -= 1;
        month += 12;
    }
    
    var A = Math.floor(year / 100);
    var B = 2 - A + Math.floor(A / 4);
    return Math.floor(365.25 * (year + 4716)) + Math.floor(30.6001 * (month + 1)) + day + B - 1524.5;
}

/*
 * Sidereal time in Greenwich
 */
function siderealTime(julianDay)
{
    var T = (julianDay - 2451545.0) / 36525;
    return toRadians(280.46061837 + 360.98564736629 * (julianDay - 2451545.0) + 0.000387933 * T * T - T * T * T / 38710000);
}

function drawStars(lat,lon,date){
  var longitude = toRadians(-lon);
  var latitude = toRadians(lat);

  var julianDay = toJulianDay(date.getFullYear(), date.getMonth()+1,date.getDate(),
                              date.getHours() + date.getTimezoneOffset() / 60,
                              date.getMinutes(), date.getSeconds());
  var size = 240;

  storage = require('Storage');
  f=storage.read("planetarium.data.csv","r");
  linestart=0;
  g.clear();

  //Common calculations based only on time
  var t = (julianDay - 2451545.0) / 36525;
  var zeta = toRadians((2306.2181 * t + 0.30188 * t * t + 0.017998 * t * t * t) / 3600);
  var theta = toRadians((2004.3109 * t - 0.42665 * t * t - 0.041833 * t * t * t) / 3600);
  var z = toRadians((2306.2181 * t + 1.09468 * t * t + 0.018203 * t * t * t) / 3600);


  let starNumber = 0;
  //Each star has a number (the position on the file (line number)). These are the lines
  //joining each star in the constellations.
  constelation_lines=[/*Orion*/[7,68],[10,53],[53,56],[28,68],/*Taurus*/[13,172],[13,340],[293,340],[29,293],
                      /*canis menor*/[155,8]];
  var starPositions = {};

  for (i=0;i<f.length;i++)
  {
    if (f[i]=='\n'){
      starNumber++;
      //console.log("Line from "+linestart.toString()+"to "+(i-1).toString());
      line = f.substr(linestart,i-linestart);
      //console.log(line);
      linestart = i+1;
      //Process the star
      starInfo = line.split(',');
      //console.log(starInfo[0]);
      starRA = parseFloat(starInfo[0]);
      starDE = parseFloat(starInfo[1]);
      starMag = parseFloat(starInfo[2]);
      //var start = new Date().getTime();
      var dec = Math.asin(Math.sin(theta) * Math.cos(starDE) * Math.cos(starRA + zeta) + Math.cos(theta) * Math.sin(starDE));
      var ascen = Math.atan2(Math.cos(starDE) * Math.sin(starRA + zeta), Math.cos(theta) * Math.cos(starDE) * Math.cos(starRA + zeta) - Math.sin(theta) * Math.sin(starDE)) + z;
      var H = siderealTime(julianDay) - longitude - ascen;
      //Compute altitude
      var alt = Math.asin(Math.sin(latitude) * Math.sin(dec) + Math.cos(latitude) * Math.cos(dec) * Math.cos(H));
      if(alt >= 0)
      {
        //Compute azimuth  
        var azi = Math.atan2(Math.sin(H), Math.cos(H) * Math.sin(latitude) - Math.tan(dec) * Math.cos(latitude));
        var x = size / 2 + size / 2 * Math.cos(alt) * Math.sin(azi);
        var y = size / 2 + size / 2 * Math.cos(alt) * Math.cos(azi);
        starPositions[starNumber] = [x,y];
        var magnitude = starMag<1.5?2:1;
        g.fillCircle(x, y, magnitude);
        if (starMag<1 && settings.starnames)
          g.drawString(starInfo[3],x,y+2);
        g.flip();

      }
    }
  }

  if (settings.constellations){
    for (i=0;i<constelation_lines.length;i++)
    {
      constelation = constelation_lines[i];
      positionStar1=starPositions[constelation[0]];
      positionStar2=starPositions[constelation[1]];
      //Both stars need to be visible
      g.setColor(0,255,0);
      if (positionStar1 && positionStar2)
        g.drawLine(positionStar1[0],positionStar1[1],positionStar2[0],positionStar2[1]);
      g.flip();
    }
  }
}

Bangle.setGPSPower(1);

var gps = { fix : 0};
var prevSats = 0;
g.clear();

var settings = require('Storage').readJSON('planetarium.settings.json',1)||
      { starnames:false,constellations:true};

g.setFontAlign(0,0);

Bangle.on('GPS',function(gp) {
  date = new Date();
  gps = gp;
  if (gp.fix) {
    lat = gp.lat;
    lon = gp.lon;
    Bangle.setGPSPower(0);
    drawStars(lat,lon,date);
  } else {
    g.setFont("Vector",20); 
    g.drawString("Waiting for position",120,120);
    g.setFont("Vector",15); 
    if (gp.satellites>prevSats || prevSats===0){
      prevSats = gp.satellites;
      g.clearRect(0,150,240,180);
      g.drawString("Got "+gp.satellites+" satellites",120,160);
    }
    g.clearRect(0,180,240,220);
    g.drawString("GMT:"+(date.getHours()+date.getTimezoneOffset() / 60)+":"+date.getMinutes()+":"+date.getSeconds(),120,200);
    g.drawString(date.getDate()+'/'+date.getMonth()+1+"/"+date.getFullYear(),120,215);
    g.flip();
  }
});