3. Working with Vector Layers | OpenLayers 3.x Cookbook

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Table Of Contents

OpenLayers 3.x Cookbook - Second Edition

By : J. Langley, Antonio Santiago

4 (1)

OpenLayers 3.x Cookbook

4 (1)

By: J. Langley, Antonio Santiago

Overview of this book

OpenLayers 3 is one of the most important and complete open source JavaScript mapping libraries today. Throughout this book, you will go through recipes that expose various features of OpenLayers 3, allowing you to gain an insight into building complex GIS web applications. You will get to grips with the basics of creating a map with common functionality and quickly advance to more complicated solutions that address modern challenges. You will explore into maps, raster and vector layers, and styling in depth. This book also includes problem solving and how-to recipes for the most common and important tasks.

Preface

Preface

What this book covers

What you need for this book

Who this book is for

Sections

Conventions

Reader feedback

Customer support

Free Chapter

1. Web Mapping Basics

1. Web Mapping Basics

Introduction

Creating a simple fullscreen map

Playing with the map's options

Managing the map's stack layers

Managing the map's controls

Moving around the map view

Restricting the map's extent

2. Adding Raster Layers

2. Adding Raster Layers

Introduction

Using Bing imagery

Using OpenStreetMap imagery

Adding WMS layers

Changing the zoom effect

Changing layer opacity

Buffering the layer data to improve map navigation

Creating an image layer

Setting the tile size in WMS layers

3. Working with Vector Layers

3. Working with Vector Layers

Introduction

Adding a GML layer

Adding a KML layer

Creating features programmatically

Exporting features as GeoJSON

Reading and creating features from a WKT

Using point features as markers

Removing or cloning features using overlays

Zooming to the extent of a layer

Adding text labels to geometry points

Adding features from a WFS server

Using the cluster strategy

Reading features directly using AJAX

Creating a heat map

4. Working with Events

4. Working with Events

Introduction

Creating a side-by-side map comparator

Implementing a work-in-progress indicator for map layers

Listening for the vector layer features' events

Listening for mouse or touch events

Using the keyboard to pan or zoom

5. Adding Controls

5. Adding Controls

Introduction

Adding and removing controls

Working with geolocation

Placing controls outside the map

Drawing features across multiple vector layers

Modifying features

Measuring distances and areas

Getting feature information from a data source

Getting information from a WMS server

6. Styling Features

6. Styling Features

Introduction

Styling layers

Styling features based on geometry type

Styling based on feature attributes

Styling interaction render intents

Styling clustered features

7. Beyond the Basics

7. Beyond the Basics

Introduction

Working with projections

Creating a custom control

Selecting features by dragging out a selection area

Transitioning between weather forecast imagery

Using the custom OpenLayers library build

Drawing in freehand mode

Modifying layer appearance

Adding features to the vector layer by dragging and dropping them

Making use of map permalinks

Index

Index

Exporting features as GeoJSON

In the earlier recipes, we saw how to read in data from different formats, such as GML and KML, but what about exporting data from a map? A user of your mapping application may want to get a copy of the vector layer data to use it somewhere else. Or perhaps, you're saving the state of a map and need to send the layer content to a server for persistent storage so that the same geometry can be retrieved later.

In this recipe, we will export the contents of a vector layer to the GeoJSON format. The source code can be found in ch03/ch03-export-geojson. Here's what we'll end up with:

How to do it…

We are going to enable the use of an export button that will output the vector layer features as GeoJSON in a text box. Follow these steps to achieve this goal:

Create the HTML file with OpenLayers dependencies. In particular, create the following:

<div id="js-map"></div>
<div>
  <h1>Exporting GeoJSON</h1>
  <form>
    <button type="submit...

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