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A radial color gradient. A radial gradient is specified as a circle that has one color at the edge and another at the center. Colors are calculated by linear interpolation based on distance from the center. This can be used to approximate the diffuse reflection of light from a point source by a sphere. [citation needed] Both CSS and SVG support ...
where r is the radial distance, φ is the azimuthal angle and θ is the polar angle, and e r, e θ and e φ are again local unit vectors pointing in the coordinate directions (that is, the normalized covariant basis). For the gradient in other orthogonal coordinate systems, see Orthogonal coordinates (Differential operators in three dimensions).
The polar angle is denoted by [,]: it is the angle between the z-axis and the radial vector connecting the origin to the point in question. The azimuthal angle is denoted by φ ∈ [ 0 , 2 π ] {\displaystyle \varphi \in [0,2\pi ]} : it is the angle between the x -axis and the projection of the radial vector onto the xy -plane.
the radial distance r along the line connecting the point to a fixed point called the origin; the polar angle θ between this radial line and a given polar axis; [a] and; the azimuthal angle φ, which is the angle of rotation of the radial line around the polar axis. [b] (See graphic regarding the "physics convention".)
The curl of the gradient of any continuously twice-differentiable scalar field (i.e., differentiability class) is always the zero vector: =. It can be easily proved by expressing ∇ × ( ∇ φ ) {\displaystyle \nabla \times (\nabla \varphi )} in a Cartesian coordinate system with Schwarz's theorem (also called Clairaut's theorem on equality ...
The pixels with the largest gradient values in the direction of the gradient become edge pixels, and edges may be traced in the direction perpendicular to the gradient direction. One example of an edge detection algorithm that uses gradients is the Canny edge detector. Image gradients can also be used for robust feature and texture matching.
A gradient-index lens with a parabolic variation of refractive index (n) with radial distance (x).The lens focuses light in the same way as a conventional lens. Gradient-index (GRIN) optics is the branch of optics covering optical effects produced by a gradient of the refractive index of a material.
Hipparchus. The concepts of angle and radius were already used by ancient peoples of the first millennium BC.The Greek astronomer and astrologer Hipparchus (190–120 BC) created a table of chord functions giving the length of the chord for each angle, and there are references to his using polar coordinates in establishing stellar positions. [2]