Ac-Layer

<ac-layer/>is a directive which is meant to define a whole layer. In case you have previous knowledge about CesiumJs, you would notice that there are lots of map objects e.g. billboard, label, etc'. In the real world - we would like to merge all of this map objects into a single entity e.g. an airplane consists of a billboard(icon) and a label.

Now, let's create a simple airplanes layer and go through it's definitions: First of all - the data source for a layer must be an RxJs stream. Second - every notification on the stream should be of type AcNotification:

export class AcNotification {
id: number;
entity?: AcEntity;
actionType: ActionType;
}
  • id - unique entity key,

  • entity- the data itself for the entity,

  • actionType- presents what happened to the entity. actionType can be one of those values:

export enum ActionType {
ADD_UPDATE,
DELETE
}

In case ADD_UPDATE is passed - the entity will be created or updated depending on if it exists or not. In case DELETE is passed - the entity will be removed from the map.

Now, Let's look at this piece of code:

<ac-map>
<ac-layer acFor="let plane of planes$" [context]="this" [store]="true">
<ac-billboard-desc props="{
image: plane.image,
position: plane.position
}">
</ac-billboard-desc>
<ac-label-desc props="{
position: plane.position,
text: plane.name,
fillColor: getColor(plane)
}">
</ac-label-desc>
</ac-layer>
</ac-map>

ac-layer - Is our current directive which presents a plan layer. Remember that the data source must be a stream? In our case the stream is planes$.

  • acFor - Is a directive which lets you decide how would you call a single plane(or a single entity on the stream) in order to write the relevant expressions inside the directive(we'll see this in a moment). It should be noticed that the format for acFor is: let {x} of {our stream}.

  • context - The context of the observable (planes$) and the cesium descriptions props (same context as getColor). Usually it will be the context of the component itself - this.

  • store - Default: false. Tells Ac-Layer if it should store the entities it receives. The entities stored in the Ac-Layer store are extends by notifications from the stream (planes$).The store is an <entity id, entity> map. This in an optional basic data store. You can you use any kind of third party data store (e.g. ngrx/store).

  • debug - Default: false. optional console printing for each received notification.

Description Components

Now, after we have defined our layer and decided that each entity on the stream will be called plane, let's drill down into the definitions of how an entity should look.

  • ac-billboard-desc - which presents billboard from CesiumJs. This directive allows you to pass props(expressions) to this billboard. You may see that although we do pass props - we actually pass expressions that are based on the plane that we defined earlier. Actually we say: 'Dear angular-cesium, please create and manage a billboard using those expressions for each plane'. Now, when an entity is passed through the stream - based on it's id, actionType and entity - angular-cesium will know what to do. When passing data with the same id and actionType=ADD_UPDATE - the entity will be updated on the map for every message.

  • ac-label-desc - the same as ac-billboard-desc but just for labels. It should be mentioned that ac-billboard-desc & ac-label-desc are all exposing the same API as Cesium expose for each map-entity.

It is important to mention that angular-cesium doesn't duplicate the description component over the DOM for each different plane in $plane (as ngFor does). why? because there is no reason to, cesium entities are drawn on the canvas map using javascript API i.e. entities aren't represented as HTML, by doing so we gain a major boost in performance.

Benefits

After explaining a little bit about ac-layer we hope that you may see it's benefits:

  • Easily defining a layer

  • Easily add/update/remove entities - all you have to do is pass a message through the stream and angular-cesium will keep track of all the rest.

  • Readable code - when reading your html which describes your layer - it is pretty easy to understand how your layer would look.

  • Maintainable code.