Importantly, the Atlas API is independent of any specific rendering library. This means it can be implemented with adapters for different libraries, and the application can switch between rendering technologies in real time.
For its initial release, Atlas was implemented for Cesium in the Atlas-Cesium library. More information on how to implement adapters for other rendering libraries is coming soon.
Atlas contains a collection of Manager objects that are responsible for maintaining state and handling events that are not object-specific, for example the array of currently-selected entities or executing a command to map the parameter values of a set of entities onto their colours.
There is one manager responsible for each major component of the system. The managers are summarised below, with each component described in more detail afterwards.
|CameraManager||Manages the position, orientation and movement of the camera in the scene. Also provides an API for setting and zooming to bookmarked viewpoints.|
|DomManager||Manages the placement and visibility of the Atlas widget in the browser DOM.|
|EditManager||Manages the editing of entities in response to user input. Logic is composed of a collection of modules for different edit modes.|
|EntityManager||Maintains a collection of created entities and provides an external interface to create, update and delete them.|
|EventManager||Manages the dispatching and bubbling of internal events, and the routing of external events.|
|InputManager||Converts user input actions into internal Atlas events that can be routed to other managers.|
|PopupManager||Manages the display of popup elements on the overlay.|
|RenderManager||Manages the appearance of terrain and imagery in the scene, and provides access to functionality of the rendering library.|
|SelectionManager||Manages selection and deselection of entities directly or within an area, and maintains a list of currently-selected entities.|
|VisualisationManager||Manages the application and removal of projections.|
For more detailed information about the Atlas managers, consult the JSDocs.
Entities and Features
The concept of an event is very general, and can mean different things in different contexts.
Within Atlas, an event is published every time something happens in one part of the system that
might be of interest to another part of the system or the host application. These events are called
intern) events, and every internal event is eventually published to the host
The host application communicates with Atlas through the same event system. Events published by the
host application into Atlas are called "external" (
extern) events. External events are more like
commands, or requests that the event be executed internally by the relevant Manager. From Atlas's
perspective, you can consider external events to be notifications that an event occurred in the host
application, and Atlas's internal state should be updated to be consistent with that event.
This distinction is important when deciding which events to listen for within Atlas. For example, an external 'entity/select' event might be published when the user selects an entity in the host application GUI, as opposed to clicking on Atlas. This event would be handled by the SelectionManager, which synchronises the internal state by selecting the specified entity within Atlas. Once the entity is selected, the SelectionManager would publish an internal 'entity/select' event so that other managers can react to the completed selection if they are interested.
Subscribing to an internal events invokes the callback after the event happens and the state has been updated. Subscribing to an external event invokes the callback when the host application requests it, which may be before or after the command is executed (depending on the order that the subscribed managers are notified).
Atlas is designed more for convenience than for comprehensive coverage of all of the intricacies of more complex GIS systems. As such, it is opinionated about some aspects of its design, meaning it imposes certain restriction to reduce ambiguity. This will come as a welcome relief to GIS novices, but may confuse experts searching for low-level configuration options.
This section lists the deliberate design decisions that have been made with respect to various complexities of GIS:
- Coordinate Projections: All location data is expressed in the same coordinate system, namely the standard WGS 84 using latitude, longitude and elevation.