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( Surface normal)
A surface normal, or simply normal, to a flat surface is a vector which is perpendicular to that surface. A normal to a non-flat surface at a point P on the surface is a vector perpendicular to the tangent plane to that surface at P. The word "normal" is also used as an adjective a line normal to a plane, the normal component of a force, the normal vector, etc. The concept of normality generalizes to orthogonality. For a polygon (such as a triangle), a surface normal can be calculated as the vector cross product of two (non-parallel) edges of the polygon. For a plane given by the equation ax + by + cz = d, the vector (a,b,c) is a normal. For a plane given by the equation r&_160;=&_160;a&_160;+&_160;ab&_160;+&_160;ßc, where a is a vector to get onto the plane and b and c are non-parallel vectors lying on the plane, the normal to the plane defined is given by b&_160;×&_160;c (the cross product of the vectors lying on the plane). If a (possibly non-flat) surface S is parametrized by a system of curvilinear coordinates x(s, t), with s and t real variables, then a normal is given by the cross product of the partial derivatives
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Surface normal Subcategories
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