Re: Photos of Petra Kvitova
The main courts at the Madrid venue are all indoor courts in all but name due to being surrounded by those metal "boxes". That's the crucial factor IMO, not altitude; Madrid is only c. 600 mts above sea level.
600 meters is not "only".. It's the difference in atmospheric pressure ~ 60 millimeters of mercury (torr).. And how these "metal boxes" can affect the ball's speed ?