in reply to [OT] Displaying 4D data in a 2D image.

Cool question! I'd use voxels, or more specifically---doxels, to get the job done. Graphics::VTK has some support for voxels. It requires The Visualization ToolKit. And for some quick examples, there's the Voxlap Engine and download here.

See also:

Wikipedia: Voxel.
Visualization Lab: Fundamentals of Voxelization.
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