Revert "Destroyed cesium integration (markdown)"

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cesium-integration.md

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+# Work packages
+## Synchronize views
+Idea: A vector on the 2D map displays the view point and the view direction:
+* When moving the 3D view, it adjusts the 2D vector.
+* When moving the 2D vector, the 3D view is adjusted.
+
+See example with OpenLayers 2 and Google Earth plugin: http://plan.epfl.ch/?lang=en, click in the right menu on 3d. 2D and 3D are snychronized. 
+
+Question: How to get the same control feeling when manipulating the Ol3 view / the Cesium view?
+Uses cases are: stacked views or separated views like for EPFL.
+
+## Smooth transition between 2d and 3d
+Idea: A la google map, share the bottom line and tilt. Forward and Backward.
+
+Some thoughts about the camera movement: https://gist.github.com/tonio/750dbc843ef95601c4be (might be outdated with the experience of the following POCs)
+
+Ongoing work:
+* 1. POC: http://bl.ocks.org/tonio/raw/9759909/
+* To be developed further: http://bl.ocks.org/gberaudo/raw/51f050326d91d4e9c09a/1b55ad64a1f3de2dcba5673ecb52f976104a4592/#
+
+Remarks:
+* all directions must be handled (not just NS and EW);
+* all tilted situations must be handled (starting from an arbitrary tilted angle);
+* always keep center of bottom line fixed in general, whole line for NS and EW.
+
+## Sync raster data sources
+Idea: If a user adds a WMS/TMS/WMTS layer to ol3.js map it should also be added to the cesium globe.
+
+Known limitations: for now, ol3js and cesium don't support the same layer type:
+ * ol3js: WMTS, WMS, OSM, Bing
+ * cesiumjs:
+  * WMS (this is not a single request, but multiple WMS tiled requests, but no WMS-C, can't specify the grid)
+  * TMS,
+  * OSM,
+  * Bing,
+  * ESRI 
+
+WMTS issue, see: https://github.com/AnalyticalGraphicsInc/cesium/issues/1890
+
+## Share vector data
+Idea: Bring vector data the user interact with in 2d into 3d. Allow same styling, labels and tooltip information.
+
+Cesium supported format:
+ * GeoJSON, OK!
+ * KML is an ongoing work: https://github.com/AnalyticalGraphicsInc/cesium/tree/kml & https://github.com/AnalyticalGraphicsInc/cesium/issues/873
+
+Cesium examples:
+* Styling:
+ * Points/Billboards: http://cesiumjs.org/Cesium/Apps/Sandcastle/index.html?src=Billboards.html&label=Showcases
+ * Polylines: http://cesiumjs.org/Cesium/Apps/Sandcastle/index.html?src=Polylines.html&label=Showcases
+ * Polygons: http://cesiumjs.org/Cesium/Apps/Sandcastle/index.html?src=Polygons.html&label=Showcases 
+ * Geometries: http://cesiumjs.org/Cesium/Apps/Sandcastle/index.html?src=Geometry%20and%20Appearances.html&label=Showcases
+* Labels: http://cesiumjs.org/Cesium/Apps/Sandcastle/index.html?src=Labels.html&label=Showcases
+* Tooltips?
+
+Notes
+ * Cesium places the 2D GeoJSON on the terrain according following rules:
+  * Vertexes are precisely placed on the terrain
+  * Segments go straight (in 3D) between the 2 Vertexes
+
+## Share edit
+Idea: use cesium picking information to get the coordinates in 3D. and send them back to the traditionnal transactional webservice
+http://cesiumjs.org/Cesium/Apps/Sandcastle/index.html?src=Picking.html&label=Showcases
+
+## Share the same user interaction
+Idea: same keyboard shortcut to rotate a map in ol3 as to rotate the globe in cesium.
+
+For now, we have:
+* rotation:
+ * ol3js: `shift` - drag
+ * cesiumjs: `control` - drag
+
+
+# Architecture
+This integration is developed in an open source layer built ontop of ol3js as ol3js is not bound to a specific 3D globe. This layer should allow to provide a common and efficient way to have ol3js and cesium working closely together.
+
+## Technical issues
+* How to keep both ol3js and cesium synchronized?
+ * Apply vector transformations (diff from current state) each time a context change?
+ * Compute from scratch a new state from the new context?
+* Save computing resources
+ * disable rendering of the underlying map or globe if it's hidden by the overlayed one
+ * still preserve context synchronization
+* Smooth transition needs to know the elevation of the destination point of the camera
+ * cesium provides an asynchronous method, synchronous planned for August
+ * cesium provides in a dev branch a specific method. TDB: WHERE?
+* Cesium camera entering the terrain
+
+ > In regards to the camera falling through the terrain, you will want to upgrade to Cesium 1.0 in August, which will include Camera/terrain interaction (see https://github.com/AnalyticalGraphicsInc/cesium/pull/1817 and https://github.com/AnalyticalGraphicsInc/cesium/issues/1670).
+