3.1.6 • Public • Published

    Zero Degree

    (React Native/Expo package)

    A module that constantly monitors and returns the direction angle of the target location as the phone rotates or moves. This is a React Native/Expo package.

    (For Github users: NPM package link -

    What It Does

    * Monitors device location (GPS) and device heading (using magnetometer sensor).
    * Constantly returns angle (in degree) between the device and the target.
    * The value returns from the module is from -179 to 180 degree; 0 degree means the device is pointed to the target perfectly.
    * It returns the degree value accurately even the phone is on hand and tilted, i.e. not perfectly horizontal.

    How To Use

    import ZeroDegree from 'zero-degree';
    let _Mecca = { latitude: 21.42287137530198, longitude: 39.82573402862004 };
    let zeroDegree = new ZeroDegree(_Mecca);
    zeroDegree.watchAsync(degree => console.log(degree));

    Use with useEffect/useState in projects. See the Complete Example below this readme or check out the demo:

    You can run the demo on a real device. Install Expo Go app (iOS app / Android app); on mobile browser, tap the demo link, it will be prompted to open the demo using Expo Go.

    Events, Props etc

    Constructor parameter: Pass an Json object containing latitude, longitude of the target location.

    const _Greenland = { latitude: 76.94606201163724, longitude: -43.474120688453034 };
    let zeroDegreeObj = new ZeroDegree(_Greenland);, onError): Instance method, to start watching the device location and device heading.

    onDegreeUpdate callback: Constantly receives the degree value of the phone heading with respect to target as the phone moves.

    await zeroDegreeObj.watchAsync(degree => console.log(degree));

    onError callback: It will be called whenever a error will be occurred, with an object as argument having error details.

       degree => console.log(degree), 
       errData => console.error(errData);

    zeroDegreeObj._getLogData: For debugging purpose. Assign a function to it to receive additional data in an object.

    zeroDegreeObj._getLogData = log => console.log(log);

    A Complete Example

    // App.js
    import React, { useState, useEffect } from 'react';
    import { Text, View } from 'react-native';
    import ZeroDegree from 'zero-degree';
    let _Mecca = { latitude: 21.42287137530198, longitude: 39.82573402862004 };
    export default function App() {
       const [degree, setDegree] = useState(null);
       const [err, setError] = useState(null);
       const [log, setLog] = useState(null);
      useEffect(() => {
        let zeroDegree;
        async function initZeroDegree() {
          zeroDegree = new ZeroDegree(_Mecca);  
          zeroDegree._getLogData = log => setLog(log); // optional
          await zeroDegree.watchAsync(degree => setDegree(Math.round(degree)),
            err => setError(err));
        return () => zeroDegree.unwatch();
       }, []);
      return (
          <Text>Target: {degree}&deg;</Text>
          <Text>Info: {JSON.stringify(log)}</Text>
          <Text>Error: {JSON.stringify(err)}</Text>

    Accuracy Tests

    Device: IPhone 7
    Location: Dhaka, Bangladesh

    Targets Result
    Mecca, Saudi Arabia OK
    Greenland (north pole) OK
    Exact north (Yeniseysky, Russia) OK
    Exact south (Indian Ocean) OK
    Exact west (Algeria) OK
    Exact east (North Pacific Ocean) OK
    New Zealand OK
    Antarctica (south pole) OK
    Nunavut, Canada OK

    To perform a reverse test, different locations were passed to the module as device's location, ignoring the GPS data.

    Target: Mecca, Saudi Arabia

    Device location Result
    Melbourne, Australia OK
    Greenland (north pole) OK*
    Indian Ocean (exact south of Mecca) OK
    Barents Sea (exact north of Mecca OK
    Timaukel, Magallanes and Chilean Antarctica, Chile OK
    South China Sea (exact east of Mecca) OK
    Antarctic Ice shield, Antarctica Seems OK*

    [*] On earth globe, Antarctic Ice shield (-75.36047491435592, -79.42558210228636) is located at south pole which is under the the globe. As a mocked location, it produces good result, but in real, magnetometer will not work on south pole as well as on north pole.


    npm i zero-degree

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    • tareq.newaz.shahriar