Hierarchical Radial Basis Function Networks for 3-D Surface Reconstruction ( Borghese and Ferrari, Neurocomputing, 1998) A constructive hierarchical RBF network for 3-D surface reconstruction from irregularly sampled data
Objectives Reconstruction of 3-D surfaces from irregularly sampled data About this presentation Presentation of the problem HRBF and wavelet MRA approaches Examples Conclusions
Laboratory of Human Motion Study & Virtual Reality - INB CNRHttp:// Autoscan 3D digitiser Manual scanning (selective sampling) Motion Capture for scanning Portable & flexible
Laboratory of Human Motion Study & Virtual Reality - INB CNRHttp:// How to go from points to meshes Problem: noise Solution: regularised reconstruction Human body parts are smooth Noise has higher frequencies than the surface Surface has been oversampled
Properties of HRBF Requires no regularly sampled 3-D data Multiresolution, coarse-to-fine (bottom-up), regularly grid, dyadic RBF network The number of layers is not determined on a a priori basis: the network grows until a convergence criterion is met RBF parameters ( , ) are constrained through sampling theory RBFs are selectively located on a regular grid based on the local error
Laboratory of Human Motion Study & Virtual Reality - INB CNRHttp:// a1(x)a1(x) a2(x)a2(x) s(x)s(x) r1(x)r1(x) r2(x)r2(x) aJ(x)aJ(x) rJ(x)rJ(x) s(x) aJ(x)aJ(x) a2(x)a2(x) a1(x)a1(x) x … a0(x)a0(x) r J-2 (x) r0(x)r0(x) … r J-1 (x) s(x) x a0(x)a0(x) r J-1 (x) r J-2 (x) s(x)s(x) a J-1 (x) a J-2 (x) r0(x)r0(x) MRA Analysis HRBF Analysis MRA Synthesis HRBF Synthesis
Laboratory of Human Motion Study & Virtual Reality - INB CNRHttp:// The surface is therefore reconstructed as: HRBF Analysis HRBF Synthesis
Multi-scale Reconstruction with HRBF
Laboratory of Human Motion Study & Virtual Reality - INB CNRHttp:// Multi-scale Reconstruction with HRBF
Laboratory of Human Motion Study & Virtual Reality - INB CNRHttp:// Multi-scale Reconstruction with HRBF
Laboratory of Human Motion Study & Virtual Reality - INB CNRHttp:// Position of the Gaussians
Laboratory of Human Motion Study & Virtual Reality - INB CNRHttp:// Multi-scale Reconstruction with Wavelet MRA
Advantages of HRBF vs wavelet MRA Coarse-to-fine (bottom-up) vs fine-to-coarse (top-down) approximation. The number of layers is not determined on a a priori basis (the network grows until a convergence criterion is met) The approximation process can be stopped at a certain level of detail having the outline of the surface with few coefficients Coefficent elimination is carried out during learning on the basis of the local error. There is no analogous mechanism in MRA. Requires no regular sampling Like MRA, HRBF features a firm foundation in data sampling theory Disadvantages of HRBF vs wavelet MRA Computational cost