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Destroyed cesium integration (markdown)

Tim Schaub
2017-09-25 23:30:21 -07:00
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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?
2D view can be in local projection or in Spherical Mercator.
## Smooth transition between 2d and 3d
Idea: A la google map, share the bottom line and tilt. Forward and Backward.
2D view can be in local projection or in Spherical Mercator.
Some thoughts about the camera movement: https://gist.github.com/tonio/750dbc843ef95601c4be (might be outdated with the experience of the following POCs)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 to following rules:
* Vertexes are precisely placed on the terrain
* Segments go straight (in 3D) between the 2 Vertexes
* Heights must be manually set to have a 3D GeoJSON.
## 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
* Google Earth (2D+3D) webmap: `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.
As 2D view can be in local projection or in Spherical Mercator and Cesium is always in WGS84, it might be needed to hook a reprojection tool (proj4js) in order to reproject the vector data between the views.
In case 2 different prohections, the backend should support the different projections. IE a WMS layer displayed in a local projection in 2D should also be avilable in WGS84 for integration in Cesium
## 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).