Real-time visualization with Volume Pro 500 Board The ability to manipulate a display of a 3D volume data set in real time on a monitor screen provides a very immediate way to gain insight into the extents, shapes and relative spatial orientations of structures. Dedicated computer hardware and software is required to perform the volume rendering calculations fast enough for real-time manipulation. Relatively low-cost hardware is now becoming available which can be run on low-cost PCs. We are currently using Mitsubishi Volume Pro 500 PCI board. This board is capable of rendering volume data of 256 x 256 x 256 voxels at a rate of up to 30 frames per second. Ray casting is done using a parallel projection algorithm. The board includes hardware-assisted support for zooming, cropping planes, slicing, multiple light sources and more, all calculated on the fly. The principal limitation of this board for our visualization effort is that it only supports parallel projections. The Volume Pro board does not provide hardware support for perspective projections, which are required to do real-time 'fly-thrus' of a volume data set. We currently use a software application originally developed by Mike Bailey at the San Diego Supercomputer Center and further developed by our graduate student X. Wang, to visualize the density distribution of the solar wind between the Sun and Earth. These 3D volume result tomographic reconstructions of heliospheric remote sensing data. Four shots are shown below. The first indicates a typical volume covered by the tomography: a sphere centered on the Sun with a radius of 1.5 AU. The remaining three show views of a reconstruction of Carrington rotation 1653. At the top-left a view from above the solar north pole looking down on the solar equator is shown. The bottom figures show side views (after zooming in on the center in the bottom-right figure). In this case, Thomson scattering observations from photometers on the two Helios spacecraft were used. This reconstruction of a solar minimum period clearly shows the spiral structure of corotating structures in the solar wind.