As three-dimensional data sets resulting from simulations or measurements become available at ever growing sizes the need for visualization tools which allow the inspection and the analysis of these data sets at interactive rates is increasing. One way to deal with the complexity is the compression of the data in such a way that the number of cells which have to be processed by the visualization mapping is reduced. Since this compression will be lossy, it is up to the user to choose between quality or speed. The decision will usually be made interactively requiring fast access to a complete hierarchy of representations of the data set at various levels of resolution. Two different approaches and visualization algorithms based upon them are presented in this paper: wavelet analysis deriving a hierarchy of coarser representations from the original data set and multilevel finite elements generating successively refined tetrahedral grids from an initially coarse triangulation.