Making prehistory: researchers digitize a cave-art gallery. (digitizing).

Not so many years ago, if you wanted to see prehistoric cave art in its original setting, you could. You might visit Altamira in Spain or Lascaux in France, where, standing in the caves of our Paleolithic ancestors, you could view the stylized and vibrant bison, horses, and other beasts they painted there some 15,000 years ago. Sadly this close-up experience is now available to few people, because by visiting the cave paintings, humans had begun to destroy them. The carbon dioxide that visitors exhaled was making the atmosphere inside the caves more acidic, dissolving the surfaces of the limestone walls and loosening the paintings. At the same time, all those tourists--as many as 1000 a day at Altamira in the 1970s--were raising temperatures inside the caves to the point where bacteria began growing on the artwork.

In order to protect the ancient illustrations, most European countries stopped widescale access to cave galleries about 25 years ago. But because the caves represented sources of national pride and income, the idea of creating life-size replicas wasn't long to follow. A notable effort in the 1980s was Lascaux II in France, for which two of the cave's galleries were reproduced using manual measurements and photogrammetry. In Spain, various government and research bodies began toying with a similar idea--a particularly ambitious reproduction of Altamira, where the paintings are notable for their beauty, use of multiple colors, and incorporation of natural rock features that create a kind of bas-relief effect.

Neocave

In 1988, Spanish agencies selected the Madrid-based replication specialists at Tragacanto to create a facsimile of Altamira that was true to the original not only in spirit, but in as many particulars as possible. Explains Sven Nebel, technical director for Tragacanto, "Replication is necessary for all painted caves visited on a massive scale. But it must be done carefully, not in a `Disney' way."

Tragacanto was able to begin the project with data provided by the National Geographic Institute of Spain, which had earlier spent eight months making point laser measurements along every 5mm of the main chamber. Tragacanto then used a Minolta VI-700 3D Digitizer to scan additional, more complicated parts of the cave at even higher resolutions. Tragacanto's Manolo Franquelo oversaw the coordination of both datasets ...