This still leaves the problem of generating the off-surface points {ðxiyiziÞ}N i¼nþ1 and the
corresponding values di. An obvious choice forf is a signed-distance function, where the di is chosen
to be the distance to the closest on-surface point. Points outside the object are assigned positive
values, while points inside are assigned negative values. These off-surface points are generated by
projecting along surface normals. In the present case, considering the unorganised point-cloud data,
normals are estimated from the vertical plane fitted in the step before, using additional information
such as scanner position to resolve the sense of the normal.