Shape Segmentation with HFP

I have just combined the fitting primitives mesh clustering (HFP) algorithm proposed by Marco Attene in is paper "Hierarchical mesh segmentation based on fitting primitives" with the prototype that produces the spherical harmonics descriptor (SHA) and cord and angle histogram (CAH) for a 3D model. The result is an application that decomposes a model using the HFP approach and then computes for each segment the corresponding descriptors. This application produces a navigable VRML file containing the segmented model. By clicking on segments it is possible to see the descriptors for that segment and even the segment alone or a possible random sampling. To view an example based on a model extracted from the ESB click on screen-shot below.

Screen-shot of shape description page.

Computation of vertex normals

Resuming the development of my OFF to VRML converter, I added one more feature: the computation of vertex normals. For this purpose I follow the method described in the Computer Graphics bible, Foley et.al "Computer Graphics: Principles and Practice in C" . In my approach I use the area of the adjacent polygons to determine the length of the normal vector.

Model with vertex normals and colored according to distance to barycenter

Coloring according to distance to barycenter

In the OFF to VRML converter, it is now possible to colorize the
mesh surface according to distances from the corresponding vertices to the object barycenter.

Mesh with surface colored according to distance to barycenter

Computing the 3D convex hull

As a new optional functionality of the OFF to VRML converter, I coded the extraction of the convex hull of a 3D shape based on the implementation of the incremental algorithm proposed by O'Rourke in "Computational Geometry in C". Despite the clear explanation of the algorithm and included code, it took me some time to adapt it to the data structure I am using. However, the expected result were achieved.

3D model and corresponding convex hull.

Identification of face normals in the VRML file

I just added one more feature to my OFF to VRML converter: the optional representation of mesh normal vectors in the resulting model. The length of these normals is directly proportional to the perimeter of corresponding polygon.

Model with surface normals.