A line generating device generates two fan-shaped beams of light at an angle to each other, and projects the beams onto an adjacent surface, where the beams are visible as lines on the surface. A user has access to the intersection of the lines, so that the intersection can be marked or otherwise used...http://www.google.com/patents/US7310887?utm_source=gb-gplus-sharePatent US7310887 - Intersecting laser line generating device
