  Direct volume rendering using ray-casting is widely used in practice. By
using GPUs and applying acceleration techniques as empty space skipping, high
frame rates are possible on modern hardware. This enables performance-critical
use-cases such as virtual reality volume rendering. The currently fastest known
technique uses volumetric distance maps to skip empty sections of the volume
during ray-casting but requires the distance map to be updated per transfer
function change. In this paper, we demonstrate a technique for subdividing the
volume intensity range into partitions and deriving what we call partitioned
distance maps. These can be used to accelerate the distance map computation for
a newly changed transfer function by a factor up to 30. This allows the
currently fastest known empty space skipping approach to be used while
maintaining high frame rates even when the transfer function is changed
frequently.
