We empirically evaluate the extent to which people perceive non-constant time and speed encoded on 2D paths. In our graphical perception study, we evaluate nine encodings from the literature for both straight and curved paths. Visualizing time and speed information is a challenge when the x and y axes already encode other data dimensions, for example when plotting a trip on a map. This is particularly true in disciplines such as time-geography and movement analytics that often require visualizing spatio-temporal trajectories. A common approach is to use 2D+time trajectories, which are 2D paths for which time is an additional dimension. However, there are currently no guidelines regarding how to represent time and speed on such paths. Our study results provide InfoVis designers with clear guidance regarding which encodings to use and which ones to avoid; in particular, we suggest using color value to encode speed and segment length to encode time whenever possible.

We investigate whether the notion of active reading for text might be usefully applied to visualizations. Through a qualitative study we explored whether people apply observable active reading techniques when reading paper-based node-link visualizations. Participants used a range of physical actions while reading, and from these we synthesized an initial set of active reading techniques for visualizations. To learn more about the potential impact such techniques may have on visualization reading, we implemented support for one type of physical action from our observations (making freeform marks) in an interactive node-link visualization. Results from our quantitative study of this implementation show that interactive support for active reading techniques can improve the accuracy of performing low-level visualization tasks. Together, our studies suggest that the active reading space is ripe for research exploration within visualization and can lead to new interactions that make for a more flexible and effective visualization reading experience.

A transmogrifier is a novel interface that enables quick, on-the-fly graphic transformations. A region of a graphic can be specified by a shape and transformed into a destination shape with real-time, visual feedback. Both origin and destination shapes can be circles, quadrilaterals or arbitrary shapes defined through touch. Transmogrifiers are flexible, fast and simple to create and invite use in casual InfoVis scenarios, opening the door to alternative ways of exploring and displaying existing visualizations (e.g., rectifying routes or rivers in maps), and enabling free-form prototyping of new visualizations (e.g., lenses).

This paper develops a framework for locally deforming either a parametric surface or hierarchical subdivision surface to match a set of positional and energy minimizing constraints. The positional constraints can be obtained from a wide variety of existing interfaces, and the framework produces a smooth, local and stable deformation through solving a simple local least-squares. We use an indexing scheme to localize optimization to only contributing control points. These points are found and measured by using basis functions or by tracking subdivision mask operations. We demonstrate our framework on B-spline and Loop subdivision surfaces.