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In differential geometry, the Gauss map of a surface is a function that maps each point in the surface to a unit vector that is orthogonal to the surface at that point. Namely, given a surface X in Euclidean space R 3 , the Gauss map is a map N : X → S 2 (where S 2 is the unit sphere ) such that for each p in X , the function value N ( p ) is ...
The definition utilizes the local representation of a surface via maps between Euclidean spaces. There is a standard notion of smoothness for such maps; a map between two open subsets of Euclidean space is smooth if its partial derivatives of every order exist at every point of the domain. [6] [7] [8]
In the mathematical field of differential geometry, the Osserman–Xavier–Fujimoto theorem concerns the Gauss maps of minimal surfaces in the three-dimensional Euclidean space. It says that if a minimal surface is immersed and geodesically complete , then the image of the Gauss map either consists of a single point (so that the surface is a ...
When a surface M is embedded in E 3, the Gauss map from M S 2 extends to a SO(2)-equivariant map between the orthonormal frame bundles E SO(3). Indeed, the triad consisting of the tangent frame and the normal vector gives an element of SO(3). In 1956 Kobayashi proved that: [58]
where is the Gauss map, and the differential of regarded as a vector-valued differential form, and the brackets denote the metric tensor of Euclidean space. More generally, on a Riemannian manifold, the second fundamental form is an equivalent way to describe the shape operator (denoted by S ) of a hypersurface,
Gauss's original statement of the Theorema Egregium, translated from Latin into English. The theorem is "remarkable" because the definition of Gaussian curvature makes ample reference to the specific way the surface is embedded in 3-dimensional space, and it is quite surprising that the result does not depend on its embedding.
Gaussian curvature is an intrinsic measure of curvature, meaning that it could in principle be measured by a 2-dimensional being living entirely within the surface, because it depends only on distances that are measured “within” or along the surface, not on the way it is isometrically embedded in Euclidean space.
These are the coordinates on M obtained by introducing the standard spherical coordinate system on the Euclidean space T p M. That is, one introduces on T p M the standard spherical coordinate system (r,φ) where r ≥ 0 is the radial parameter and φ = (φ 1,...,φ n−1) is a parameterization of the (n−1)-sphere.