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OPEN LAYERS
OPEN LAYERS
HistoryGoogle Maps◦ Announced on February 2005◦ Possibility to explore the world
OpenLayers◦ First release on June 2006◦Open alternative to Google Maps and Bing made by a group of MetaCarta
employees
History
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What is OpenLayer?◦an API for building web mapping applications◦pure client-side object-oriented JavaScript, using components
from Prototype.js and the Rico library ◦AJAX (Asynchronous JavaScript and XML)◦efficient tiling◦BSD licensed (standard licence for open source software)
The Map….◦The map is the central piece on a web mapping application
and is represented by instances of the OpenLayers.Map class◦The map has some important properties:
projection, resolutions(zoom levels), units, etc◦A map contains one or more layers◦A map can contain one or more controls
The Map….
The Map….
The Map…The map has plenty of methods to deal with:
◦LayersaddLayer(), getLayer(), removeLayer(), ...◦ControlsaddControl(), getControl(), removeControl(), ...◦To move around:zoomTo(), zoomIn(), zoomOut(), pan(), panTo(), ...
The Layers…
◦The concept of Layer allows us to group/classify the elements that must be rendered on the Map
◦All layers inherit from the base class OpenLayers.Layer
The Layers…defines some common properties for all subclasses:
The Layers…We can classify layers in two main categories:◦Raster (for imagery) Raster layers show imagery from different service providers: Google, Bing, a WMS server, OSM, etc
◦Vector (for features)Vector layers allows us to work with features loaded from a data source...A feature is digital representation of something in the real world: city, river, mountain, ...
The Layers…
Raster Layers…
Vector Layers…
The Layers…◦The protocol determines the way a vector layer
communicates with a data source (HTTP,…). It must be an instance of some of the OpenLayers.Protocol subclasses
◦The format determines how features must be read or written. It must be an instance of some of the OpenLayers.Format subclasses
The Layers…When a layer must be drawn:◦The layer calls the protocol so it can load the data◦The protocol communicates with the data source and reads
the data◦The protocol uses the specified format to transform the data
into features and add them to the layer◦The layer delegates to the renderer the task to render
the features◦The renderer draws each feature
The Layers…
OpenLayers differentiates two kinds of layers:
Base layers and Overlays
The Layers…
The Layers…
◦Base layers are mutually exclusive, only one can be shown at a time
◦There can be any number of OverLays◦The isBaseLayer() property inherited from OpenLayers.Layer
determines the kind of the Layer
The Truth About OpenLayer…
◦Most of the JavaScript code we write with OpenLayers is transformed into HTML elements !!!
The Truth About OpenLayer…
The Controls…
◦Controls allows to interact with the Map◦All controls inherits from base class OpenLayers.Control
The Controls…
◦Controls allows to interact with the Map◦All controls inherits from base class OpenLayers.Control◦OpenLayers offers controls for almost any required
action: navigation, zoom, feature selection,feature edition, etc
The Controls…
Here is the output
Another output ( Vector layer )
Thanks for You Attention…
