Segments alignment is one of the fundamental factors affecting the shape of the PSF of a segmented mirror telescope. Tilt and piston of each segment must be very well and uniformly adjusted in relation with the rest of the segments. The Hartmann-Shack sensor is very efficient in detecting the local wavefront tilt, but the task to take measurements of piston using this sensor is annoying enough specially when the wavefronts are affected by atmospheric turbulence. We show, with numerical simulations, that curvature sensing is sensitive enough in order to detect piston errors in the segmented mirrors, even in the presence of the atmospheric turbulence. It would permit the taking of measurements of piston with natural stars during observation time.