Integrating OpenLayers 3 with Cesium Viewer

Question

I'm developing using Cesium built on top of Cesium.Viewer. Cesium lacks some features so I wish to integrate with OpenLayers. I'd like to add existing OpenLayers layers to the Cesium.Viewer as if they were "imagery layers".

I've found ol3-cesium, however this only allows an entire OpenLayers map instance to be visualized on a Cesium.Scene which it creates for you. Cesium.Viewer also creates an instance of Cesium.Scene targeted at a given DOM element.

How can I add OpenLayers layers to a Cesium.Viewer?

Some code snippets for illustration

var olLayer1= new ol.layer.Tile({
  source: new ol.source.MapQuest({layer: 'sat'})
});
var olLayer2= new ol.layer.Vector({
  source : ol.source.Vector();
});

var map = new ol.Map({
  layers: [olLayer1, olLayer2],
  target: 'map',
  view: new ol.View({
  })
});

Existing Cesium viewer

var viewer = new Cesium.Viewer('cesium-map', {});
// viewer setup code

ol3-cesium initialization - but this doesn't allow usage with existing viewer??

var ol3d = new olcs.OLCesium({map: map}); // map is the ol.Map instance

Answer 1

I just looked through the initialization code for OL3-Cesium and while it is essentially a wrapper on top of Cesium, the means that they decided to implement a Cesium environment is not going to play nicely if you want a hybrid Cesium.Viewer and an OL3 object.

I'm not sure of your comfort level with modifying JS libraries, but what I personally would do is make my own ol3 cesium viewer class. Something like this gist I just threw together.

Just a warning, I have not tested this code yet. You may have to make some additional modifications if you receive errors. There may be a reason that the OL3-Cesium developers choose not to use the Cesium widget or viewer to initialize Cesium in their library, but I see no reason this wouldn't work.

Here is the constructor, but you would want the whole Gist as a separate file in your ol3-cesium library. Put it in the same directory as the ol3Cesium.js file.

excerpt from https://gist.github.com/maikuru/9e650bf88aed84982667

olcs.OLCesiumViewer = function(options) {

    /**
     * @type {!ol.Map}
     * @private
     */
    this.map_ = options.map;

    var fillArea = 'position:absolute;top:0;left:0;width:100%;height:100%;';

    /**
     * @type {!Element}
     * @private
     */
    this.container_ = goog.dom.createDom(goog.dom.TagName.DIV,
            {style: fillArea + 'visibility:hidden;'});

    var targetElement = goog.dom.getElement(options.target || null);
    if (targetElement) {
        goog.dom.appendChild(targetElement, this.container_);
    } else {
        var vp = this.map_.getViewport();
        var oc = goog.dom.getElementByClass('ol-overlaycontainer', vp);
        if (oc) {
            goog.dom.insertSiblingBefore(this.container_, oc);
        }
    }

    /**
     * Whether the Cesium container is placed over the ol map.
     * @type {boolean}
     * @private
     */
    this.isOverMap_ = !goog.isDefAndNotNull(targetElement);

    /**
     * @type {!HTMLCanvasElement}
     * @private
     */
    this.canvas_ = /** @type {!HTMLCanvasElement} */
            (goog.dom.createDom(goog.dom.TagName.CANVAS, {style: fillArea}));
    this.canvas_.oncontextmenu = function() { return false; };
    this.canvas_.onselectstart = function() { return false; };

    goog.dom.appendChild(this.container_, this.canvas_);

    /**
     * @type {boolean}
     * @private
     */
    this.enabled_ = false;

    /**
     * @type {!Array.<ol.interaction.Interaction>}
     * @private
     */
    this.pausedInteractions_ = [];

    /**
     * @type {?ol.layer.Group}
     * @private
     */
    this.hiddenRootGroup_ = null;

    /**
     * @type {!Object.<Cesium.Viewer.Options>}
     * @private
     */
    var cesiumViewerConfig_ = (options.viewer || {}).scene3DOnly = true;

    /**
     * @type {!Cesium.Viewer}
     * @private
     */
    this.viewer_ = new Cesium.Viewer(this.container_, cesiumViewerConfig_);

    /**
     * @type {!Cesium.Scene}
     * @private
     */
    this.scene_ = this.viewer_.scene;

    var sscc = this.scene_.screenSpaceCameraController;
    sscc.inertiaSpin = 0;
    sscc.ineartiaTranslate = 0;
    sscc.inertiaZoom = 0;

    sscc.tiltEventTypes.push({
        'eventType': Cesium.CameraEventType.LEFT_DRAG,
        'modifier': Cesium.KeyboardEventModifier.SHIFT
    });

    sscc.tiltEventTypes.push({
        'eventType': Cesium.CameraEventType.LEFT_DRAG,
        'modifier': Cesium.KeyboardEventModifier.ALT
    });

    sscc.enableLook = false;

    this.scene_.camera.constrainedAxis = Cesium.Cartesian3.UNIT_Z;

    /**
     * @type {!olcs.Camera}
     * @private
     */
    this.camera_ = new olcs.Camera(this.scene_, this.map_);

    /**
     * @type {!Cesium.Globe}
     * @private
     */
    this.globe_ = this.scene_.globe;
    this.scene_.skyAtmosphere = new Cesium.SkyAtmosphere();

    var synchronizers = goog.isDef(options.createSynchronizers) ?
            options.createSynchronizers(this.map_, this.scene_) :
            [
                new olcs.RasterSynchronizer(this.map_, this.scene_),
                new olcs.VectorSynchronizer(this.map_, this.scene_)
            ];

    for (var i = synchronizers.length - 1; i >= 0; --i) {
        synchronizers[i].synchronize();
    }

    if (this.isOverMap_) {
        // if in "stacked mode", hide everything except canvas (including credits)
        var credits = goog.dom.getNextElementSibling(this.canvas_);
        if (goog.isDefAndNotNull(credits)) {
            credits.style.display = 'none';
        }
    }

    this.camera_.readFromView();

    this.cesiumRenderingDelay_ = new goog.async.AnimationDelay(function(time) {
        this.scene_.initializeFrame();
        this.handleResize_();
        this.scene_.render();
        this.enabled_ && this.camera_.checkCameraChange();
        this.cesiumRenderingDelay_.start();
    }, undefined, this);
};