# Define new 3D graphics primitives in Mathematica 9 [duplicate]

I have generated a three-dimensional probability distribution function (PDF) and I would like to place a series of these PDFs at certain coordinates on a cuboid. I've rasterized the PDF so it is a 3D pixelated object. The easiest way I can think of to to place the PDF on the cuboid is use ListPointPlot3D and use pointmarkers set to my PDF. It appears that I need to convert the three dimensional PDF into a Graphics3D primitive. Does anyone have any suggestions on how to do this? Thanks.

For Example:

PDFcoords = {{0, 0, 300}, {-2*978, -2*978, 300}, {2*978, 2*978,
300}, {2*978, -2*978, 300}, {-2*978, 2*978, 300}}; PDFcubPlot =
ListPointPlot3D[PDFcoords];
Cube = Graphics3D[Cuboid[{-2100, -2100, 0}, {2100, 2100, 300}]];
Sphere1 = Graphics3D[Sphere[{0, 0, 300}, 90]];
Sphere2 = Graphics3D[Sphere[{-2*978, -2*978, 300}, 90]];
Sphere3 = Graphics3D[Sphere[{2*978, 2*978, 300}, 90]];
Sphere4 = Graphics3D[Sphere[{2*978, -2*978, 300}, 90]];
Sphere5 = Graphics3D[Sphere[{-2*978, 2*978, 300}, 90]];
Show[Sphere1, Sphere2, Sphere3, Sphere4, Sphere5, PDFcubPlot, Cube]


However, instead of spheres, I want to create my own primitive graphic that I can place on the cuboid.