Accessing user current location in the app is a common practice nowadays. Depending on the usage of the location data, a common use case is to present the data in a sorted by distance filter.

Say, a restaurant app, where you want to see the nearest restaurant first.

I have been fortunate to work on a complicated geolocation aware app, where I need to track the changes of the GPS location over time.

Think of it like a fitness app, or a more popular example will be the pokemon app.

 

#### The existing solution

While most app would be enough with a listener watching for the GPS location update, the one I am working on needs more.

Basically, it is a fitness app to track jogging pattern. It needs to work when the app is in background, and offline (for some of the time).

The current available location listener `watchPosition` seems to be great for the work, until it is not.

 

#### The problem

The app needs to work together with a geo-fencing ability to detect if a user is within an action zone, where it will trigger a log, and the network request (if network connection is good).

So the main challenge is to get it to work when the app is in background, and I want to be able to detect the event as soon as the user enters the zone.

 

#### Background geolocation to the rescue

In order to be able to achieve that, this package ([https://github.com/mauron85/react-native-background-geolocation](https://github.com/mauron85/react-native-background-geolocation)) has done incredible work the background location.

However it is not a silver bullet for all the problems out there, the app I wanted to build are meant for fitness and jogging, so there are a different configuration needed to be able to adapt to my use case.

 
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#### Key takeaway

Couple the package with other features, such as drawing the jogging path on a map, show the geo-fencing zone on the map is more reliable and complete thanks to a more frequent location updates, event in the background.

It is advisable to create a couple of `.gpx` files to mock the location, otherwise the development with geolocation would be miserably slower.

More about this part in the future. Now that you know how to get location updates even app is in the background, you will be able to build a better app!

Background geolocation

Sometimes, your app needs more than just accessing the current location.

For example, you want to watch the location over time, whether to show it on the map or other features than make use of the location.

We can provide a current location for the simulator, however, we can't provide a lists of locations that showing the movement of the app over time with the default simulator settings.

Luckily for us, as developer, we are able to mock the locations of the app using `.gpx` file.

 

##### How it works

 

`.gpx` is a format to save GPS data. Basically it contains latitude, longitude and the timestamps at which the points are at.

A simple `.gpx` file looks like this.

```
<?xml version="1.0"?>
<gpx version="1.1" creator="gpxgenerator.com">
<wpt lat="3.109193" lon="101.461774">
 <ele>7.00</ele>
 <time>2018-01-04T08:08:05Z</time>
</wpt>
<wpt lat="3.109562" lon="101.461968">
 <ele>7.00</ele>
 <time>2018-01-04T08:08:20Z</time>
</wpt>
<wpt lat="3.109193" lon="101.461774">
 <ele>6.96</ele>
 <time>2018-01-04T08:08:35Z</time>
</wpt>
</gpx>
```

When you have that file, add it to your xcode, and you will be able to use the coordinates in your simulator with a toggle.

![demo](gpx-xcode.png)

So for my case, I am having 3 different paths I created for development and testing purpose. Each of them in its own `.gpx` file.

Select any one, and the simulator will pick up the location and changes over time.

 

##### End

Now you have different coordinates as time passes returned from the simulator to test.

Background geolocation

December 17, 2018

GPS testing with .gpx file

December 20, 2018