Orkhan Jafarov

Posted on Sep 11, 2020

Real Compass on mobile browsers with Javascript

#tutorial #javascript #webdev

Well, one day I had a challenge from my muslim friend to code a map that's gonna show an arrow from his current geolocation to Qibla or any geopoint.

That wasn't the best solution, cause a compass will solve it better way and make people's life easier. So, I've started to find any package/lib to put the compass into his webpage.

Found these solutions Compass.js or this one, but none of them work ~~at all~~ well. Cause last commits were 6-7 years ago.

Let's make own real compass for mobile browsers!

Result we're gonna have

We will need several html elements.

<div class="compass">
  <div class="arrow"></div>
  <div class="compass-circle"></div>
  <div class="my-point"></div>
</div>
<button class="start-btn">Start compass</button>

Let's add css for that

.compass {
  position: relative;
  width: 320px;
  height: 320px;
  border-radius: 50%;
  box-shadow: 0 0 15px rgba(0, 0, 0, 0.2);
  margin: auto;
}

.compass > .arrow {
  position: absolute;
  width: 0;
  height: 0;
  top: -20px;
  left: 50%;
  transform: translateX(-50%);
  border-style: solid;
  border-width: 30px 20px 0 20px;
  border-color: red transparent transparent transparent;
  z-index: 1;
}

.compass > .compass-circle,
.compass > .my-point {
  position: absolute;
  width: 80%;
  height: 80%;
  top: 50%;
  left: 50%;
  transform: translate(-50%, -50%);
  transition: transform 0.1s ease-out;
  background: url(https://cdn.onlinewebfonts.com/svg/img_467023.png) center
    no-repeat;
  background-size: contain;
}

.compass > .my-point {
  opacity: 0;
  width: 20%;
  height: 20%;
  background: rgb(8, 223, 69);
  border-radius: 50%;
  transition: opacity 0.5s ease-out;
}

JavaScript time!

Define our html elements first and add event for button that starts it.
iOS needs to have manipulation by user to start DeviceOrientationEvent, but for Android it works without it.

const compassCircle = document.querySelector(".compass-circle");
const startBtn = document.querySelector(".start-btn");
const myPoint = document.querySelector(".my-point");
let compass;
const isIOS = !(
  navigator.userAgent.match(/(iPod|iPhone|iPad)/) &&
  navigator.userAgent.match(/AppleWebKit/)
);

function init() {
  startBtn.addEventListener("click", startCompass);
}

function startCompass() {
  if (isIOS) {
    DeviceOrientationEvent.requestPermission()
      .then((response) => {
        if (response === "granted") {
          window.addEventListener("deviceorientation", handler, true);
        } else {
          alert("has to be allowed!");
        }
      })
      .catch(() => alert("not supported"));
  } else {
    window.addEventListener("deviceorientationabsolute", handler, true);
  }
}

function handler(e) {
  compass = e.webkitCompassHeading || Math.abs(e.alpha - 360);
  compassCircle.style.transform = `translate(-50%, -50%) rotate(${-compass}deg)`;
}

init();

Done! Our compass is working for both iOS and Android.

Upgrade our compass to reach the goal

On this step we need to find correct angle/degree to our point (Qibla).
We put the point coordinates and calculate degree from out current geolocation.

How it works?

We're getting our current geolocation
Define point coordinates (where we should turn to)
Calculate degree from our position to defined point
Display point when we're in correct position

Define pointDegree and our functions for this.

let pointDegree;

function locationHandler(position) {
  const { latitude, longitude } = position.coords;
  pointDegree = calcDegreeToPoint(latitude, longitude);

  if (pointDegree < 0) {
    pointDegree = pointDegree + 360;
  }
}

function calcDegreeToPoint(latitude, longitude) {
  // Qibla geolocation
  const point = {
    lat: 21.422487,
    lng: 39.826206,
  };

  const phiK = (point.lat * Math.PI) / 180.0;
  const lambdaK = (point.lng * Math.PI) / 180.0;
  const phi = (latitude * Math.PI) / 180.0;
  const lambda = (longitude * Math.PI) / 180.0;
  const psi =
    (180.0 / Math.PI) *
    Math.atan2(
      Math.sin(lambdaK - lambda),
      Math.cos(phi) * Math.tan(phiK) -
        Math.sin(phi) * Math.cos(lambdaK - lambda)
    );
  return Math.round(psi);
}

We put our location handler into init function to listen Geolocation API. Add some code to handler that's gonna update our point state.

function init() {
  startBtn.addEventListener("click", startCompass);
  navigator.geolocation.getCurrentPosition(locationHandler);
}

function handler(e) {
  compass = e.webkitCompassHeading || Math.abs(e.alpha - 360);
  compassCircle.style.transform = `translate(-50%, -50%) rotate(${-compass}deg)`;

  // ±15 degree
  if (
    (pointDegree < Math.abs(compass) && pointDegree + 15 > Math.abs(compass)) ||
    pointDegree > Math.abs(compass + 15) ||
    pointDegree < Math.abs(compass)
  ) {
    myPoint.style.opacity = 0;
  } else if (pointDegree) {
    myPoint.style.opacity = 1;
  }
}

We're done! We have a real compass in our mobile browsers.

Demo link

Here's a source link

by @gigantz

Top comments (8)

Emil Totev • Feb 24 '21

Hey, thank you for the great tutorial! I've got it working flawlessly on iOS, but there appears to be an issue on Android - North is always in the direction the phone is pointing when the page loads, and if you're not looking north, all the directions are miscalculated. Have you faced this issue and were you able to overcome it?

Orkhan Jafarov • Feb 24 '21

I hope your Android device was using GPS with high accuracy mode. If not it will not work as expected. Try to get or debug heading value from geolocation or compassHeading. I didn’t faced this issue on Android

MUzairS15 • Aug 31 '21

Can someone help me understand this code, why are we calculating pointdegree and all, we can do only with e.webkitcompassheading (this will give the required movement from north position ) isn't it??
And also we are transforming compass with value of 'compass' so what purpose does other functions serve??

Javed Shaikh • Dec 28 '20

This is great. Thanks for sharing 👏👏

jespoting • Apr 5 '22

Hi, it worked perfectly for me. I would like to ask a question to see if you can help me.

How could I in this same project if I pass by GET both the longitude and latitude of the destination to update it every 5 seconds.

That is to say:
1- Instead of having the latitude and longitude defined in the variable, that the longitude and latitude were passed by get and update every 5 seconds the latitude and longitude in case it has moved.

Thanks in advance

deinstern24 • May 7 • Edited

Thanks a lot for this, I do have some problems with it though:
for some reason, the compass keeps "jumping" around. On first load north is determined accurately, but with a few of those "jumps" it is lost.
One more ting: turning my mobile 180° when pointing north does not turn exactly to south, but quite bit more.
Any clue what might cause this behaviour?

Edit: I did recalibrate my device's compass, no change.