With a laser.
And, needless to say, the new scanner is once again made out of Lego. It's less of a mechanical achievement than the last one, because the Lego isn't much more than a supporting framework for the DAVID 3D Scanner software, that works with a line laser and a webcam.
It's way faster than the pokey-scanner, though, and has startlingly good resolution. Lego isn't generally much use for making precision mechanisms, but this one seems to work great.