Trigonometric functions are mathematical functions of an angle. There are six basic trigonometric functions (sine (sin), cosine (cos), tangent (tan), cotangent (cot), secant (sec), cosecant (cosec)), commonly defined as ratios of two sides of a right triangle. Used in diagnostic imaging for Cartesian sampling, to describe radio frequency signals, etc.

Conversion of the analog signal to a series of digital values by measurement at a set of particular times; this utilizes the analog to digital converter. If the rate of sampling is less than twice the highest frequency in the signal, aliasing will occur. The duration of sampling determines how small a difference of frequencies can be separated.

See also Algorithm, Trigonometric Functions, Digitization, Exponential Functions, Imaginary Number, Logarithms, Point Spread Function.