  Approaches to ground surface reconstruction from massive terrestrial point
clouds are presented. Using a set of local least squares (LSQR) planes, the
"holes" are filled either from the ground model of the next coarser level or by
Hermite Radial Basis Functions (HRBF). Global curvature continuous as well as
infinitely smooth ground surface models are obtained with Partition of Unity
(PU) using either tensor product B-Splines or compactly supported exponential
function. The resulting surface function has local control enabling fast
evaluation.
