  Halo is one of the most important basic elements in cosmology simulation,
which merges from small clumps to ever larger objects. The processes of the
birth and merging of the halos play a fundamental role in studying the
evolution of large scale cosmological structures. In this paper, a visual
analysis system is developed to interactively identify and explore the
evolution histories of thousands of halos. In this system, an intelligent
structure-aware selection method in What You See Is What You Get manner is
designed to efficiently define the interesting region in 3D space with 2D
hand-drawn lasso input. Then the exact information of halos within this 3D
region is identified by data mining in the merger tree files. To avoid visual
clutter, all the halos are projected in 2D space with a MDS method. Through the
linked view of 3D View and 2D graph, Users can interactively explore these
halos, including the tracing path and evolution history tree.
