Before revision:   We analyze the errors that arise in the estimation of a 3D shape index from 2D imagery , and find that typically only a few dozen cells in 2D imagery are required to reduce uncertainty in the mean 3D shape index below 2\\%.
After revision:  Using cell vertex model geometries, we find that the distribution of 2D shapes allows clear determination of the mean value of a 3D shape index. We analyze the errors that arise in the estimation of a 3D shape index from 2D imagery , and find that typically only a few dozen cells in 2D imagery are required to reduce uncertainty in the mean 3D shape index below 2\\%.