  Animated transitions help viewers understand changes between related
visualizations. To clearly present the underlying relations between statistical
charts, animation authors need to have a high level of expertise and a
considerable amount of time to describe the relations with reasonable animation
stages. We present AniVis, an automated approach for generating animated
transitions to demonstrate the changes between two statistical charts. AniVis
models each statistical chart into a tree-based structure. Given an input chart
pair, the differences of data and visual properties of the chart pair are
formalized as tree edit operations. The edit operations can be mapped to atomic
transition units. Through this approach, the animated transition between two
charts can be expressed as a set of transition units. Then, we conduct a
formative study to understand people's preferences for animation sequences.
Based on the study, we propose a set of principles and a sequence composition
algorithm to compose the transition units into a meaningful animation sequence.
Finally, we synthesize these units together to deliver a smooth and intuitive
animated transition between charts. To test our approach, we present a
prototype system and its generated results to illustrate the usage of our
framework. We perform a comparative study to assess the transition sequence
derived from the tree model. We further collect qualitative feedback to
evaluate the effectiveness and usefulness of our method.
