CustusX  16.5
An IGT application
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Architecture

Overview

CustusX uses a layered architecture, with external libraries at the bottom, a resource layer consisting of reusable components and classes, a plugin layer for handling of extensibility, modularity and state, a logic layer for system management, and a top layer proving the user interface.

External libraries

The Qt framework is used throughout the application, at the same level as the C++ libraries. Qt greatly simplifies C++ development through its signals and slots mechanism and extensive libraries. VTK and ITK are used for visualization and image processing, CTK for plugins and DICOM, Eigen for basic math, while DCMTK, OpenCV, OpenIGTLink and IGSTK are used for specialized operations.

CustusX uses a Superbuild for handling many of the external libraries.

Resource Layer

A collection of common utility classes available to everyone.

The Resource Layer consists of building blocks that are available to everyone. Everything here is/should be reusable, i.e. used by at least two other modules.

The Core library is the basic component, all other libraries depend on that and are specialized in some way.

In principle, this layer contains no global state, but a few exceptions exist:

Plugin Framework

CustusX use the OSGi-based CTK Plugin Framework as the basis for the plugin part of the architecture. This framework introduces two central concepts: Services and plugins (OSGi uses the name bundle instead of plugin). Services are abstract interfaces that are available from the central plugin framework, which is implemented as a singleton software pattern. Service consumers are unaware of the service providers. Services may also appear and disappear at any time. Plugins are physical components (shared libraries) that can be loaded and unloaded at runtime. Each plugin provides one or more service implementations, while they also can act as service consumers.

Core Services

An IGT platform requires some core services in order to operate. These are declared as interfaces in the resource layer, thus making them available to everyone. They are implemented as plugins that always are included with the system, and it is assumed to be one instance of each:

cx::SessionStorageService Persistent storage of sessions, corresponding to documents in other applications.
cx::PatientModelService Represents the virtual patient, containing image data, geometric models, and spatial and temporal relations between these.
cx::TrackingService Access to physical and simulated navigation tracking systems.
cx::VideoService Access to video sources, such as endoscopes and ultrasound probes.
cx::ViewService Framework for displaying the geometric data in a 3D scene. Several 2D and 3D views visualize the data from various directions and combinations.

Some services are not widely used. The interfaces are declared inside each plugin, thus requiring plugins to depend on them. It is assumed to be zero or one instance of each:

cx::RegistrationService Perform Image-to-Patient registration and Image-to-Image registration.
cx::AcquisitionService Record Video and Tracking data for later use.
cx::UsReconstructionService Create a 3D volume from a sequence of US images with tracking information.

Extension Points

Services can also be used as extension points, i.e. adding more instances of the same service adds more functionality to the system. Currently the following extension points are available:

cx::GUIExtenderService Provide a collection of widgets and toolbars that can be added to for example the cx::MainWindow. This is the most generic extension point and can be used for anything that can be accessed from a GUI.
cx::RegistrationMethodService Defines an Image-Patient or Image-Image registration method that is made available through the cx::RegistrationService.
cx::ReconstructionMethodService Defines a US reconstruction method that is made available through the cx::UsReconstructionService.
cx::StreamerService Support for a video source or an ultrasound scanner. Used by the cx::VideoService.
cx::Filter Defines an algorithm that can be applied to volume or geometric data.

Logic Layer

The Logic Layer, with cx::LogicManager as the main class, manages the plugin framework and application lifecycle.

GUI Library

The GUI Layer contains user interface components that are available to the application, and works on top of the Logic Layer. That means that the library has access to all installed plugins and the Resource Layer.

Application Layer

The application layer mostly consist of a single main() function which calls the cx::LogicManager and GUI. The default application is CustusX, which uses cx::MainWindow as frontend. See Customize Applications for how to create your own applications.