Tu Ying, Shen Han-Wei
Computer Science and Engineering Department, Ohio State University, Ohio, USA.
IEEE Trans Vis Comput Graph. 2008 Nov-Dec;14(6):1157-64. doi: 10.1109/TVCG.2008.114.
The treemap is one of the most popular methods for visualizing hierarchical data. When a treemap contains a large number of items, inspecting or comparing a few selected items in a greater level of detail becomes very challenging. In this paper, we present a seamless multi-focus and context technique, called Balloon Focus, that allows the user to smoothly enlarge multiple treemap items served as the foci, while maintaining a stable treemap layout as the context. Our method has several desirable features. First, this method is quite general and hence can be used with different treemap layout algorithms. Second, as the foci are enlarged, the relative positions among all items are preserved. Third, the foci are placed in a way that the remaining space is evenly distributed back to the non-focus treemap items. When Balloon Focus enlarges the focus items to a maximum degree, the above features ensure that the treemap will maintain a consistent appearance and avoid any abrupt layout changes. In our algorithm, a DAG (Directed Acyclic Graph) is used to maintain the positional constraints, and an elastic model is employed to govern the placement of the treemap items. We demonstrate a treemap visualization system that integrates data query, manual focus selection, and our novel multi-focus+context technique, Balloon Focus, together. A user study was conducted. Results show that with Balloon Focus, users can better perform the tasks of comparing the values and the distribution of the foci.
树形图是可视化层次数据最流行的方法之一。当树形图包含大量项目时，以更高的细节级别检查或比较一些选定的项目变得非常具有挑战性。在本文中，我们提出了一种无缝的多焦点和上下文技术，称为气球聚焦，它允许用户平滑地放大多个用作焦点的树形图项目，同时保持稳定的树形图布局作为上下文。我们的方法具有几个理想的特性。首先，该方法非常通用，因此可以与不同的树形图布局算法一起使用。其次，随着焦点的放大，所有项目之间的相对位置得以保留。第三，焦点的放置方式使得剩余空间均匀地分配回非焦点树形图项目。当气球聚焦将焦点项目放大到最大程度时，上述特性确保树形图将保持一致的外观并避免任何突然的布局变化。在我们的算法中，使用有向无环图（DAG）来维护位置约束，并采用弹性模型来控制树形图项目的放置。我们展示了一个集成了数据查询、手动焦点选择和我们新颖的多焦点+上下文技术——气球聚焦的树形图可视化系统。进行了一项用户研究。结果表明，使用气球聚焦，用户可以更好地执行比较焦点的值和分布的任务。
