CesiumJS - Entity / Graphics Hierarchie in relation to performance

问题

I am working on a Wysiwyg Editor for CesiumJS content. The user will be able to create many points, lines and other graphics, connect them according to definable relations and group them in separate Groups.

Now I am wondering what the best practises are in terms of performance. At the moment I create one PointPrimitiveCollection for each Group and then add points:

group.points = scene.primitives.add(new Cesium.PointPrimitiveCollection());

and then

group.points.add({
   position : cartesian,
   ...
});

for each new point.

Polygons are created using:

network.hull_polygon = viewer.entities.add({
        name : 'xxx',
        polygon : {
            hierarchy : Cesium.Cartesian3.fromDegreesArray(points_array),
            material : color,
            ...
        }
    });

polylines similarly.

Now since the Objects can also be dragged around / animated, I was wondering where Cesiums entity logic would come in?

Thanks for all help!

回答1:

Cesium's Entity logic is useful primarily for objects that move along a known path over time, for example the flight plan of an aircraft in the future, or a GPS recording of the route taken by a vehicle in the past. Such routes can be loaded into the Entity system (often via CZML), and the user can run the simulation time forwards and backwards at arbitrary speeds, to review the routes of all the vehicles. The Entity system owns the logic for updating graphics primitive positions based on simulation time changes.

Entities are also often used as a quick way to make some disparate graphics primitives associate with each other. For example, a polygon, a point, and a label can all be created as a single Entity even if they are three separate graphics primitives at the same location. This saves a bit of effort on the part of the application developer, and doesn't hurt performance too much since the properties involved are all marked as constants, so the Entity layer knows not to update them with simulation time.

But, it sounds like you may have a case where paths are not known in advance. For things like user interactive edits or real-time telemetry being received, the Entity system can't know what's coming up next, so its whole system for updating positions from simulation times is not doing you any good. In that case it may be better to skip the Entities, and deal exclusively with graphics primitives for this. This would mean you need to write your own update function to alter graphics positions as new information is being received, similar to the Entity layer's update functions, but based on your own live inputs instead of recorded paths.

Note that the public "Sandcastle" demos only include Entity demos. But, if you download and build the source for Cesium and run Sandcastle locally from a dev build, a separate tab appears in the Sandcastle Gallery called Development that shows a whole set of demos based on graphics primitives as opposed to Entities. This can be useful for seeing examples of how to control things at this layer.

Hopefully this is helpful in understanding how the different layers of Cesium interact.

来源：https://stackoverflow.com/questions/58837720/cesiumjs-entity-graphics-hierarchie-in-relation-to-performance

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