I was looking at some videos on the construction of the Golden State Warriors' new arena in SF and I noticed that apart from a large number of tower cranes, at the phase of construction shown in the link below, there are two "x cranes". More accurately they are like large construction machines (like a bulldozer) bearing a huge steel boom that crosses another one to form a giant X. They have cables on them but I have never seen anything like that and couldn't really figure out what their function might be. Anyone know?
You can see them most clearly around the 2 min mark.