Destroyed Development Phase 1 (markdown)
elemoine
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# OpenLayers 3 Phase 1
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This document defines the functionality that OpenLayers 3 will offer as the
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result of the first development phase.
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Stated and anticipated future client requirements necessitate architectural
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considerations in Phase 1 to ensure that this functionality can be implemented
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later phases. Each section of the document includes an *Enabling future
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functionality* for that matter.
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## Animation
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In Phase 1 we will make OpenLayers 3 animate
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* Zoom transition
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* Panning (kinetic)
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* Tile displaying
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* Camera movement
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### Enabling future functionality
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This requires a solid and flexible framework that makes animations possible
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with both the WebGL and the DOM renderers.
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Animations with WebGL will be based
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on *requestAnimationFrame* loops, while, for performance reasons, animations
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with DOM will be based on CSS3 transitions. The animation framework should
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accomodate both implementations.
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Related to the animation framework is the way the DOM renderer translates
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and scales the layers pane. The DOM renderer currently scales each tile
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image individually by changing the dimensions of its DOM element. For
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performance reasons we may instead want to apply a CSS scale transform
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on container elements.
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We will implement the animation framework in Phase 1,
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as a foundation for current and future animation requirements.
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## Camera
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In Phase 1 we will experiment with 3D features. We will work on
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* Integrating with the Cesium virtual globe
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* Adding "limited tilt" support (i.e. tilt with same-resolution tiles)
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### Enabling future functionality
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For 3D in general, and integration with virtual globes in particular, we need
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to introduce the concept of a camera. In Phase 1 we will therefore add a Camera
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type. The Camera will be part of the API. One requirement though is that the
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API remain easy for developers of "simple", 2D map applications.
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## Data Source
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OpenLayers 3 has the concept of data sources. One type only is currently
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supported: *tile*. (OpenLayers 3 currently supports the XYZ/OSM tile source
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family, and tiled WMS.)
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In Phase 1 we will add support for the following layer type:
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* WMTS
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* Single Image WMS
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* Image (OpenLayers 2's `OpenLayers.Layer.Image`)
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* Vector (detailed in the following section)
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### Enabling future functionality
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To be able to rate-control, abort, prioritize tile requests, and manage
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resource management a Tile Queue (or Tile Manager) will be implemented.
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This work will be based on past experience with OpenLayers 2 and WebGLMaps.
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Also, writing custom, application-specific layer/data source types should be
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possible. The architecture and build tool must be designed with this
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in mind.
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Vector
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------
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In Phase 1 we will add the following vector functionality:
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* Display styled points, linestrings and polygons with Canvas 2D (or SVG [*])
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* Display unstyled points with WebGL
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* Draw, interact with, and modify features
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* Support various *formats*, *protocols*, and *strategies*
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We will consider 2D vectors only in Phase 1.
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[*] To be decided considering performance and browser compatibility.
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Note: it is not yet clear whether we will have a Markers layer type as in OpenLayers 2.
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### Enabling future functionality
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OpenLayers 2 offers many vector-related features. It has a flexible
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architecture enabling to work with different *strategies*, *protocols*, and
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*formats*. It also provides a powerful styling framework, based on SLD.
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Eventually, OpenLayers 3 will, at least, provide the same level of
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functionality and flexibility.
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Displaying styled geometries of any type (point, linestring and polygon) with
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WebGL must also be possible in the future, and it must exhibit good
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performance. For example, sending the vector data to the GPU must not require
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expensive memory operations (data copies), and it must be possible to batch the
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drawing of multiple objects.
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Also, applying styles to geometries should probably be easier than with
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OpenLayers 2, but without compromising on flexibility and performance.
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## Control
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In Phase 1 we will port the following OpenLayers 2 controls, or
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functionality thereof, to OpenLayers 3:
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* ArgParser
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* Attribution
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* MousePosition
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* Navigation
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* PanZoomBar
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* Permalink
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* ScaleLine
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* TouchNavigation
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* Zoom
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* ZoomToMaxExtent
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* OverviewMap
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* DrawFeature
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* Geolocate
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* GetFeature
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* Measure
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* ModifyFeature
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* NavigationHistory
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* SelectFeature
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OpenLayers 2 includes a `Panel` control, for addings buttons onto a map.
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Whether something similar will be be ported to OpenLayers 3 is yet to be
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determined.
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### Enabling future functionality
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The control architecture will be built with the following requirements in mind:
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* Controls must work with both the DOM and WebGL renderers.
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* Controls can be composed of other controls.
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* Writing controls must be easy.
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* Working with application-specific controls should be possible.
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Note: OpenLayers 3 has *interactions* and *controls*. We will need to clarify
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these concepts in order to implement the required functionality in a generic
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way.
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## Format
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In Phase 1 we will implement the following formats:
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* WMS Capabilities
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* WMTS Capabilities
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* GeoJSON (implies JSON)
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* KML
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* WKT
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* GPX
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* WFTS (implies GML)
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### Enabling future functionality
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OpenLayers 2 includes an architecture to work with XML (mainly OGC), and share
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code between various formats. A similar architecture will be implemented in
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OpenLayers 3.
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We will also attempt to make it possible to share formats with other
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open-source toolkits (Cesium, Leaflet). This may require collaboration with
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other communities.
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* Define format architecture
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* define XML format architecture
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## Mobile
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OpenLayers 3 must obviously work on mobile. Panning and zooming should be very
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smooth. The common gestures for interacting with the map should be available.
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For example, we will add a `PinchZoom` interaction (which we don't have
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currently).
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We will focus on supporting the iOS and Android native browsers (WebKit). See
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the Browser Support section below for more information.
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## Overlay/Popup
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OpenLayers 3 already includes the concept of overlays. Overlays are
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things/elements that can be added atop the map. This is the concept onto which
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popups and labels will rely. We will to continue this work, and add a popup
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implementation based on the overlay architecture.
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## Browser support
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In Phase 1 we will make sure the features we develop work in
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* IE 9+
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* FireFox 17+
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* Chrome 22+
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* Safari 5+
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* iOS 6 and Android 4.2 native browsers
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Supporting IE from version 9 makes it possible to not rely on VML at all for
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vector rendering. VML is an obsolete technology.
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### Enabling future functionality
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OpenLayers 3 will need to be able to leverage modern web technologies such
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as Filter Effects and CSS3 (3D) transforms.
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## Infrastructure and Doc
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OpenLayers 3 needs to have good documentations and tools.
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We already generate an API doc using jsdoc3, but a lot
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more remains to be done for a decent API documentation. We may need to extend
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jsdoc3 to meet our needs.
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We use Travis CI for Continuous testing and integration. We will need to
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update our Travis script as we go.
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OpenLayers 3 has to offer easy-to-use tools for creating custom builds of the
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library. A convenient command line interface (CLI) will be developed. This CLI
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will serve as the base for a hosted build tool developed in a further phase of
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the project.
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We will also need to organize the website and the community around two code
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bases (OpenLayers 2 and OpenLayers 3).
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## Summary
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In the first phase of development we will mainly work on porting the
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functionality from OpenLayers 2 to OpenLayers 3. At the end of the first phase
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OpenLayers 3 should major features of OpenLayers 2, and should have a solid and
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flexible architecture making it possible, and easy enough, to add more features
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in the future.
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In the first phase we will also work on more advanced features (e.g. Cesium
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integration, client-side re-projection, millions of geometries handled by
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WebGL, limited tilt close to the surface). The goal is twofold: assess our
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architecture and design choices, and show off OpenLayers 3 to the public.
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