Tomographci devices often produce data with directionally and spatially dependent resolution. Resampling to cubic voxels is possible at the cost of a significant increase of data volume and rendering time. We present an algorithm for direct ray tracing of rectilinear grids, which enables the implementation of surface rendering with subvoxelsurface detection based on local interpolation, as well as different volume rendering technique (color compositing, reprojection, maximum intensity projection). Further we present a faster version of the basic algorithm based on cubic macro-regions assigned to each background voxel. Each macro-region is defined by its chessboard distance to the nearest foreground voxel and can be skipped during the scene traversal. The speed-up is thus gained by increasing the step along the ray, maintaining 6-connectivity of the ray in the object vicinity, which is necessary for correct surface detection.
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