Trying to figure out this laser pen trick. Anyone know how this works?

Question

Here is the link to the video. I'm trying to figure out what they are using to do do this with. http://emuse.ebaumsworld.com/video/watch/14338

Answer 1

This is really cool. The artist wields a laser pen to "write" on the building, but a separate laser is keeping the image. There's already in existence laser-optical systems whereby the image is captured by camera with a CCD for a real-time output, which goes to a computer for image processing, which then drives a more poweful laser that sends a beam right back out the same optical system back to the object, illuminating it. Repetitive scanning of this laser beam "keeps" the image on the object, or building. What the camera and computer does, of course, is to do an "before and after" image comparsion, so that when the artist "writes" with his laser pen, the computer notes the shift in illumination levels and thus creates an image in its memory for the 2nd laser to project onto the object. That's why the artist's laser pen doesn't have to be connected to anything else.

Answer 2

A very powerful projection system. Watch the video carefully again, and look at what's in the van.

It would appear that they're actually tracking his hand movements to define the projection, but there's no guarantee of that.