OpenLayers Cookbook

OpenLayers Cookbook

Overview of this book

Data visualization and analysis has become an important task for many companies. Understanding the basic concepts of GIS and knowing how to visualize data on a map is a required ability for many professionals today. OpenLayers is a JavaScript library to load, display, and render maps from multiple sources on web pages."OpenLayers Cookbook" teaches how to work with OpenLayers, one of the most important and complete open source JavaScript libraries.Through an extensive set of recipes, this book shows how to work with the main concepts required to build a GIS web applicationñ maps, raster and vector layers, styling, theming, and so on."OpenLayers Cookbook" includes problem solving and how-to recipes for the most common and important tasks. A wide range of topics are covered.The range of recipes includes: creating basic maps, working with raster and vector layers, understanding events and working with main controls, reading features from different data sources, styling features, and understanding the underlying architecture."OpenLayers Cookbook" describes solutions and optimizations to problems commonly found.

OpenLayers Cookbook

Credits

About the Author

About the Reviewers

www.PacktPub.com

Preface

Free Chapter

Web Mapping Basics

Introduction

Creating a simple full screen map

Different ways to include OpenLayers

Understanding base and non-base layers

Avoiding the need of a base layer

Playing with the map's options

Managing map's stack layers

Managing map's controls

Moving around the map view

Restricting the map extent

Adding Raster Layers

Introduction

Using Google Maps imagery

Using Bing imagery

Adding WMS layer

Wrapping the date line options

Changing the zoom effect

Changing the layer opacity

Using WMS with single tile mode

Buffering the layer data to improve the map navigation

Creating an image layer

Setting the tile size in WMS layers

Working with Vector Layers

Introduction

Adding a GML layer

Adding a KML layer

Creating features programmatically

Reading and creating features from a WKT

Adding markers to the map

Using point features as markers

Working with popups

Adding features from a WFS server

Using the cluster strategy

Filtering features in WFS requests

Reading features directly using Protocols

Working with Events

Introduction

Creating a side-by-side map comparator

Implementing a work in progress indicator for map layers

Listening for vector layer features' events

Listening for non-OpenLayers events

Adding Controls

Introduction

Adding and removing controls

Adding a navigation history control

Working with geolocation

Placing controls outside the map

Editing features on multiple vector layers

Modifying features

Measuring distances and areas

Getting feature information from data source

Getting information from the WMS server

Theming

Introduction

Understanding how themes work using the img folder

Understanding how themes work using the theme folder

Delimiting tiles in a raster layer

Creating a new OpenLayers theme

Starting actions outside the controls

Styling Features

Introduction

Styling features using symbolizers

Improving style using StyleMap and the replacement of feature's attributes

Playing with StyleMap and the render intents

Working with unique value rules

Defining custom rules to style features

Styling clustered features

Beyond the Basics

Introduction

Working with projections

Retrieving remote data with OpenLayers.Request

Creating a custom control

Creating a custom renderer

Selecting features intersecting with a line

Making an animation with image layers

Index

Customer Reviews

5 star

4 star

3 star

2 star

1 star

Avoiding the need of a base layer

There can be situations where you don't want a base layer and only want a bunch of layers to work on.

Imagine an online GIS editor where users can add and remove layers but they are not obligated to have an always visible one.

This recipe shows how we can easily avoid the requirement of setting a base layer within the map.

How to do it...

As always, create a DOM element to render the map:

<div id="ch1_avoid_baselayer" style="width: 100%; height: 100%;"></div>

Now create a new OpenLayers.Map instance and set the allOverlays property to true:

// Create the map using the specified DOM element 
var map = new OpenLayers.Map("ch1_avoid_baselayer", { 
    allOverlays: true 
});

Add two layers to see a result. Also add the layer switcher control:

// Add a WMS layer 
var wms = new OpenLayers.Layer.WMS("OpenLayers WMS Basic","http://vmap0.tiles.osgeo.org/wms/vmap0", 
{ 
    layers: 'basic' 
}); 
map.addLayer(wms); 
// Add a WMS layer 
var topo = new OpenLayers.Layer.WMS("USA Topo Maps", "http://terraservice.net/ogcmap.ashx", 
{ 
    layers: "DRG" 
},
{ 
    opacity: 0.5 
}); 
map.addLayer(topo); 
// Add LayerSwitcher control 
map.addControl(new OpenLayers.Control.LayerSwitcher());

Center the map view to some nice place:

// Set view to zoom maximum map extent 
// NOTE: This will fail if there is no base layer defined 
map.setCenter(new OpenLayers.LonLat(-100, 40), 5);

How it works...

When the map's property allOverlays is set to true, the map ignores the isBaseLayer property of the layers.

If you expand the layer switcher control, you will see that it contains two overlay layers, no base layer, which you can show or hide and, if desired, leave a blank map without layers.

In addition, in this recipe we have used the map.setCenter() method, which needs a position, an OpenLayers.LonLat instance, and a zoom level to work.

There's more...

When working in the allOverlays mode, the lowest layer will act as base layer, although all the layers will be flagged as isBaseLayer is set to false.

OpenLayers Cookbook

OpenLayers Cookbook

Overview of this book

Related Content you might be interested in

Current Title:

OpenLayers Cookbook

Avoiding the need of a base layer

How to do it...

How it works...

There's more...

See also