The final application will be a mobile dashboard view for the employees of our little start-up which they can either take on the road or use at Gelary HQ to plan their work. It will consist of a map and a floating control panel behind a menu button. The map is used to visualise a route, starting from the user's current position along a series of customers, and the traffic situation along the route. The control panel will enable our delivery drivers to search for nearby ice cream shops, display turn-by-turn directions as well as to calculate the best pick-up location for a group of selected customers. The app will also be able to handle order changes: e.g. if a customer cancels or updates his or her position, the route will automatically be recalculated.
What will we learn in this tutorial?
In the previous and very first post in our series we've learned how to acquire credentials for HERE's API services, render a basic map view, control the maps basic functionality through code and how to place a marker with a custom icon. If you haven't read it — we'd recommend to check it out before moving on.
In this post we will request the user's current physical location via his or her web browser's geolocation API and update the map accordingly. Sounds good? Let's get to it!
Browser Geolocation API
The Geolocation API has been supported by browsers for quite some time. Even Internet Explorer has enabled its use since version 9.
Before we start using this API in our little app, let's take a look at some of its methods. Them method names give a good idea as to what they do:
|Method ||Description |
|getCurrentPosition() ||Obtain the user's current location. |
|watchPosition() ||Watch the user's location and trigger a callback every time it changes. |
|clearWatch() ||Stop watching a user's location. |
Let's start by looking at getCurrentPosition. This method gives us the current geolocation of a device. It takes three arguments:
- The success callback function which takes a position object as input parameter.
- The error callback function which takes an error object as input parameter.
- And an options object for further configuration options.
However, the getCurrentPosition will give only give you a user's location once. This won't do for our little ice cream delivery application — we want to know where we are at all times while we're racing to deliver the cold goods!
This is where watchPosition comes into play. This method takes exactly the same arguments as getCurrentPosition but the success function will be called every time the position of the device changes.
Great! Let's start using this handy API in our application. In scripts/app.js add the following lines at the bottom:
It's really that simple! This short piece of code will re-center the map every time the user's position changes and render a marker for the new location. Excellent!
When you go and refresh your browser you will likely be asked for permission to use your location via a small dialog in order to protect your privacy:
Note: We recommend to use Firefox for this tutorial as Google Chrome restricts the use of the Geolocation API if requested from a file:/// URI. If you'd like to continue to use Chrome for we recommend to use a small development server locally.
Pro tip: watchPosition returns an id which may be used to call clearWatch later in order to stop watching for location updates:
Today we have learned to create another important piece of our ice cream delivery app: figuring out where we. A few small lines in our code, a giant leap towards am ice cream-driven economy. In the next post we are going to explore how to navigate on a map and how to find routes. Stay tuned!