Many students have difficutly visualizing three dimensional images when what is presented to them is two dimensional - be it a drawing on the board or a picture in a book. While some computer programs can let you "manipulate" three dimensional objects, so as to view them from different angles, the student is still seeing the object on a two dimensional surface - the computer screen.
The idea behind SPECTRE is to present these images to students in the way they should be presented - three dimensionally. This allows the student to actually walk around the object, view it from different angles, and get a better feeling and understanding of the image presented.
How does it work? SPECTRE is a basic editing tool that allows users to create a "scene" or collection of three dimensional shapes (be it cubes, spheres, etc). SPECTRE then takes these shapes and creates a series of "slices" (two dimensional intersections of the objects at regular intervals) and prints these out onto transparencies. When these transparencies are layered (with a bit of room between them) over a light source, the viewer sees a remarkable recreation of the entire object.