This paper describes a new method to recover the sign of the local Gaussian curvature at each point on the visible surface of a 3-D object. Multiple (p > 3) shaded images are acquired under different conditions of illumination. The required information is extracted from a 2-D subspace obtained by applying Principal Components Analysis (PCA) to the p-dimensional space of normalized irradiance me...

Let M be an n(n ≥ 3)-dimensional complete connected hypersurface in a unit sphere S(1). In this paper, we show that (1) if M has non-zero mean curvature and constant scalar curvature n(n−1)r and two distinct principal curvatures, one of which is simple, then M is isometric to the Riemannian product S( √ 1− c2) × Sn−1(c), c = n−2 nr if r ≥ n−2 n−1 and S ≤ (n−1)n(r−1)+2 n−2 + n−2 n(r−1)+2 . (2) i...

Given a smooth surface, a blue (red) ridge is a curve along which the maximum (minimum) principal curvature has an extremum along its curvature line. Ridges are curves of extremal curvature and therefore encode important informations used in segmentation, registration, matching and surface analysis. State of the art methods for ridge extraction either report red and blue ridges simultaneously o...

This paper revisits one of the puzzling behaviors in a developable cone (d-cone), the shape obtained by pushing a thin sheet into a circular container of radius R by a distance η. The mean curvature was reported to vanish at the rim where the d-cone is supported. We investigate the ratio of the two principal curvatures versus sheet thickness h over a wider dynamic range than was used previously...

The fact that the Darboux frame is rotation–minimizing along lines of curvature of a smooth surface is invoked to construct rational surface patches whose boundary curves are lines of curvature. For given patch corner points and associated frames defining the surface normals and principal directions, the patch boundaries are constructed as quintic RRMF curves, i.e., spatial Pythagorean–hodograp...

In this paper we present a novel method to estimate curvature of iso grey-level surfaces in grey-value images. Our method succeeds where isophote curvature fails. There is neither a segmentation of the surface needed nor a parametric model assumed. Our estimator works on the orientation field of the surface. This orientation field and a description of local structure is obtained by the Gradient...

In [12], we treated the Christoffel-Minkowski problem as a convexity problem of a spherical hessian equation on S via Gauss map. In this paper, we study the curvature equations of radial graphs over Sn. Our main concern is the existence of hypersurface with prescribed Weingarten curvature on radial directions. For a compact hypersurface M in Rn+1, the kth Weingarten curvature at x ∈ M is define...

Dupin cyclides are algebraic surfaces of order three and four whose lines of curvature are circles. These surfaces have a variety of interesting properties and are aesthetic from a geometric and algebraic viewpoint. Besides their special property with respect to lines of curvature they appear as envelopes of one-parameter families of spheres in a twofold way. In the present article we study two...

Li and Zaidi (Vision Research 40 (2000) 217; 41 (2001) 1519) have recently argued that there are two necessary conditions for the perception of 3D shape from texture: (1) the texture pattern must have a disproportionate amount of energy along directions of principal curvature; and (2) the surface must be viewed with a noticeable amount of perspective. In the present article we present evidence ...