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 – geometries in action


The last example only used one linear ring for the polygon. Let's use the Web Inspector's console to create a polygon and then add a linear ring to see what happens. Open the vector_template.html file in your browser and then open the Web Inspector's Console. We'll be typing the commands into the console directly and observing the result on the map.

  1. First, create a polygon using the preceding example:

    var polygon = new ol.geom.Polygon([ [ [-20,-20],[-20,20],[20,20],[20,-20],[-20,-20] ] ]);
  2. We'll need to reproject the coordinates into our view's projection:

    polygon.transform('EPSG:4326', 'EPSG:3857');
  3. Now, we'll need a source and a layer:

    var source = new ol.source.vector({
      features: [new ol.Feature(polygon)],
      projection: 'EPSG:4326'
    });
    var layer = new ol.layer.vector({
      source: source,
      style: vectorStyle
    });
  4. And add it to the map:

    map.addLayer(layer);
  5. You should see something like the following screenshot:

  6. Now create a linear ring that will make a hole...