Book Image

OpenLayers 3: Beginner's Guide

By : Thomas Gratier, Paul Spencer, Erik Hazzard
Book Image

OpenLayers 3: Beginner's Guide

By: Thomas Gratier, Paul Spencer, Erik Hazzard

Overview of this book

<p>This book is a practical, hands-on guide that provides you with all the information you need to get started with mapping using the OpenLayers 3 library.</p> <p>The book starts off by showing you how to create a simple map. Through the course of the book, we will review each component needed to make a map in OpenLayers 3, and you will end up with a full-fledged web map application. You will learn the key role of each OpenLayers 3 component in making a map, and important mapping principles such as projections and layers. You will create your own data files and connect to backend servers for mapping. A key part of this book will also be dedicated to building a mapping application for mobile devices and its specific components.</p>
Table of Contents (22 chapters)
OpenLayers 3 Beginner's Guide
Credits
About the Authors
About the Reviewers
www.PacktPub.com
Preface
Index

Time for action – reprojecting geometries in vector layers


When you draw in OpenLayers, you draw in local projections' features. Then, if you need, for example, to exchange data source with a third party, sometimes you need to make reprojections. It's useful to know how to consume data and reproject them or on the contrary, export them. It's what we will see here:

  1. Again, let's copy the previous sample into a new file in the sandbox directory.

  2. Edit the file, and after the var projection declaration, add a new GeoJSON source, a vector source:

    var countriesSource = new ol.source.GeoJSON({
       projection: 'EPSG:2154',
       url: '../assets/data/nutsv9_lea.geojson'
     });
  3. Add a listener on the source that fires once and that sends some console.log statements:

    countriesSource.once('change', function(evt) {
      if (this.getState() == 'ready') {
        console.log(this.getFeatures()[0].getGeometry().getCoordinates());
        console.log(this.getFeatures()[0].getGeometry().clone().transform('EPSG:2154','EPSG:4326'...