  Upcoming HI surveys will deliver large datasets, and automated processing
using the full 3-D information (two positional dimensions and one spectral
dimension) to find and characterize HI objects is imperative. In this context,
visualization is an essential tool for enabling qualitative and quantitative
human control on an automated source finding and analysis pipeline. We discuss
how Visual Analytics, the combination of automated data processing and human
reasoning, creativity and intuition, supported by interactive visualization,
enables flexible and fast interaction with the 3-D data, helping the astronomer
to deal with the analysis of complex sources. 3-D visualization, coupled to
modeling, provides additional capabilities helping the discovery and analysis
of subtle structures in the 3-D domain. The requirements for a fully
interactive visualization tool are: coupled 1-D/2-D/3-D visualization,
quantitative and comparative capabilities, combined with supervised
semi-automated analysis. Moreover, the source code must have the following
characteristics for enabling collaborative work: open, modular, well
documented, and well maintained. We review four state of-the-art, 3-D
visualization packages assessing their capabilities and feasibility for use in
the case of 3-D astronomical data.
