I didn't pay attention to the tower crane before, I often used the construction site. I didn't think about how it increased.
I accidentally found out that the people in the abroad have explain the elevation of the tower crane through the picture.
Http://www.dot.state.ga.us/preconstruction/bridgedesign/sidney/mainspan/crane/twcranim.gif
Refresh can be seen,
I have learned my knowledge again.
