A Two-Level Differential
Volume Rendering Method for Time-Varying-Volume-Data
Shih-Kuan Liao, Yeh-Ching
Chung[1], Jim Z.C. Lai
Department
of Information Engineering
Feng
Chia University, Taichung, Taiwan 407, ROC
Tel:
886-4-24517250 x3765
Fax:
886-4-24516101
Email:
{skliao, ychung, lai}@fcu.edu.tw
The differential volume
rendering method is a ray casting based method for
time-varying-volume-data. In the
differential volume rendering method, the changed fractions of volume data
between consecutive time steps are extracted to form differential files. Based on the differential files, only
the changed pixels, instead of all the pixels in the image, are updated by
casting new rays at the positions in each time step. The main overhead of the differential volume rendering
method is to determine the changed pixel positions before casting new rays for
the changed pixels. In this paper,
we propose a two-level differential volume rendering method, which is a
modified differential volume rendering method with faster determination of the
changed pixel positions. In the proposed method, the
determination of the changed pixel positions is accelerated by the aid of
second-order-difference. Since
voxels in two consecutive differential files may partially overlap in the
space, the computation spent on determining the changed pixel positions due to
the overlapped area is redundant.
We use this property to extract the difference of changed voxel
positions between consecutive differential files to form the second-order-difference. Based on the second-order-difference,
the changed pixel positions can be determined efficiently. The experimental results show that the
proposed method outperforms the differential volume rendering method for all
test datasets.
Keywords: Ray casting,
differential volume rendering, time-varying-volume-data, flow animation, CFD.