Step 1. Mapping the tablets
|The laser scanner mapping a large cuneiform tablet, approximately the size of a standard sheet of paper, 8 x 11 inches.|
How does it work? A very precise set of electrical motors drives our system, panning the laser head over the object, which is fixed to a stage, from side to side, say, from left to right. When one pass is completed, the stage automatically moves over and the laser head make another sweep - in the opposite direction, like the other half of one scribbling motion - and so on until the whole surface is scanned. The head basically takes 14,400 snapshots per second of the ruby red laser light as it bounces off the object, using a pair of charge coupled devices (CCDs) likes the ones in your digital camera. They "look" at the object from fixed angles, like two telescopes taking aim at a distant star. While the computer records the latitude and longitude, x,y position, of each laser spot by following the stage and laser head, it also uses trigonometry to calculate the vertical height (z of the x,y,z series) of each reflected point on the basis of where the reflected light strikes the two CCDs. Using our high resolution system, we are able to collect data a very fine level of detail by setting the inter-point spacing between each locator spot at a distance as small as .001 inches (=.025 mm or 25 microns).
The laser zips along to complete a rectangular sweep across a tablet according to the instructions we give it, where to start and where to stop. Once one side of the object is done we turn it over, remount it and scan the back surface and then all the edges, repeating the process until the whole thing is mapped. Software then stitches together the different views to form a perfect-copy, virtual tablet that is visualized and can be manipulated on screen. computer graphics terms, however, this digital replica is not an image. It is a "solid model." Like a hard object, it has length, breadth and thickness, and since we know the precise x,y,z location of every dot making up the solid model it is a relatively simple matter for the computer to extract that information by touching the surface with a cursor and clicking the mouse. In other words, the GPS coordinates plus altitude of spot of a cuneiform sign is registered, and with these registration points each sign can be defined, outlined and measured.