A model for strategy in constraint solving

The use of constraints for the definition of graphical user interfaces has been recognized as a great concept. However, often many valuations of the variables will satisfy the constraints, and which particular valuation matches best with the expectation of the user cannot be decided without further information. Three typical examples of user interfaces are presented where this occurs, and from these, requirements on a more cooperative constraint solver are derived. A new method for the definition and implementation of the strategy to decide which variables to adapt is presented. The model is based on two notions: hierarchy and grouping. Variables are divided into groups, and for each group three parameters are set. These are used to determine the level of variables, dependent on which group they belong, and which variables are modified. These levels are used in turn to select the variables to be adapted. An implementation of this method is described, as part of the Computational Steering Environment (CSE) developed at CWI. The resulting constraint solver can handle simultaneous sets of non-linear, multi-way constraints; and can handle a high-level definition of the strategy to be followed. Finally, the results are discussed, and suggestions for further work are done

Steering smog prediction

The use of computational steering for smog prediction is described. This application is representative for many underlying issues found in steering high performance applications: high computing times, large data sets, and many different input parameters. After a short description of the smog prediction model, its visualization and steering are described. The amount of computation needed to solve the governing transport equations is alarmingly high. The user has a large number of options for the display of various aspects of the simulation, and also for the interactive control of its input data. Smooth animation is very important to monitor the evolution of pollutants and for a responsive feedback to parameter changes. Here a performance of least 15 frames per second is required. We discuss techniques that allow the user to steer the numerical solver, such that an optimal tradeoff between computation speed and accuracy can be made

Parametrizable cameras for 3D computational steering

We present a method for the definition of multiple views in 3D interfaces for computational steering. The method uses the concept of a point-based parametrizable camera object. This concept enables a user to create and configure multiple views on his custom 3D interface in an intuitive graphical manner. Each view can be coupled to objects present in the interface, parametrized to (simulation) data, or adjusted through direct manipulation or user defined camera controls. Although our focus is on 3D interfaces for computational steering, we think that the concept is valuable for many other 3D graphics applications as well

CSE: a modular architecture for computational steering

Computational steering is the ultimate goal of interactive simulation. Steering enables users to supervise and dynamically control the computation of an ongoing simulation. We describe CSE: a modular architecture for a computational steering environment. The kernel of the architecture is designed to be very simple, flexible and minimalistic. All higher level system functionality is pushed into modular components outside of the kernel, resulting in a rich and powerful environment. For these modular components (called satellites) a uniform user interface metaphor for users, based on a tray of cards, has been used. The card tray metaphor is very simple to understand and provides users with a simple mechanism to organize and retrieve the tools. Several applications of the environment are shown

Logging in a computational steering environment

Logging of input and output variables is very useful in computational steering. In this paper we describe how we added logging functionality to a computational steering environment developed at CWI. We show how a 2D interface can be augmented with logging by using the third dimension for the display of the logged variables. The user specifies which graphical representations of variables must be logged, and this log is displayed together with the current state of the simulation. Two examples show that logging in computational steering gives more insight in the simulation, that it can be used for monitoring, and that it can be used to undo erroneous actions

3D computational steering with parametrized geometric objects

Computational Steering is the ultimate goal of interactive simulation: researchers change parameters of their simulation and immediately receive feedback on the effect. We present a general and flexible graphics tool that is part of an environment for Computational Steering developed at CWI. It enables the researcher to interactively develop his own interface with the simulation. This interface is constructed with 3D Parametrized Geometric Objects. The properties of the objects are parametrized to output data and input parameters of the simulation. The objects visualize the output of the simulation while the researcher can steer the simulation by direct manipulation of the objects. Several applications of 3D Computational Steering are presented

Interactive exploration and modeling of large data sets: a case study with Venus light scattering data

We present a system where visualization and the control of the simulation are integrated to facilitate interactive exploration and modeling of large data sets. The system was developed to estimate properties of the atmosphere of Venus from comparison between measured and simulated data. Reuse of results, distributed computing, and multiple views on the data were the major ingredients to create an effective environment

Pixel masks for screen-door transparency

Rendering objects transparently gives additional insight in complex and overlapping structures. However, traditional techniques for the rendering of transparent objects such as alpha blending are not very well suited for the rendering of multiple transparent objects in dynamic scenes. Screen-door transparency is a technique to render transparent objects in a simple and efficient way: No sorting is required and intersecting polygons can be handled without further preprocessing. With this technique, polygons are rendered through a mask: Only where the mask is present, pixels are set. However, artifacts such as incorrect opacities and distracting patterns can easily occur if the masks are not carefully designed. In this paper, first the requirements on the masks are considered. Next, three algorithms are presented for the generation of pixel masks. One algorithm is designed for the creation of small (e.g. 4 $times$ 4) masks. The other two algorithms can be used for the creation of larger masks (e.g. 32 $times$ 32). For each of these algorithms results are presented and discussed

Computational steering

The traditional cycle in simulation is to prepare input, execute a simulation, and to visualize the results as a post-processing step. However, more insight and a higher productivity can be achieved if these activities are done simultaneously. This is the underlying idea of Computational Steering: researchers change parameters of their simulation on the fly and immediately receive feedback on the effect. In this paper the Computational Steering Environment, CSE, developed at CWI is described. We discuss the requirements of computational steering environment, its relation with high performance computing and networking, and show an application of its use