def points(self, number = None):
"""
selection convex points in the image
number --- the slice number in the volume
"""
if number:
PointBuilder = ImageProcessing.KeyPoints(self._volume_data[:,:,number])
else:
sx, sy, sz = self._volume_data.shape
PointBuilder = ImageProcessing.KeyPoints(self._volume_data[:,:,sz//2])
return PointBuilder
