A Fast Multithreaded Out-of-Core Visualization Technique

Out–of–core rendering techniques are necessary for viewing large volume disk–resident data sets produced by many scientific applications or high resolution imaging systems. Traditional visualizers can provide real–time performance but require all of the data to be viewed to be in the RAM. We describe a multithreaded implementation of an out–of–core isosurface renderer that does not impose such restrictions and yet provides performance that scales well with the size of the data. Our renderer uses an interval tree data structure on disk with a layout that reduces disk seeks to read out only the relevant data from the disk. The low resulting disk latencies are hidden by using prefetching and multithreading to overlap the activities of the rendering computations and disk accesses. Our renderer outperforms the out–of–core isosurface renderer of the well–known vtk toolkit by about one order of magnitude and several orders of magnitude when compared against vtk toolkit’s optimized in–core algorithm on large representative CT scan data. The multithreaded version also scales well with the number of threads.