The INTERPOL function performs linear, quadratic, or spline, interpolation on vectors with a regular or irregular grid.
This routine is written in the IDL language. Its source code can be found in the file
interpol.pro in the
lib subdirectory of the IDL distribution.
For regular grids: Result = INTERPOL( V, N [, /LSQUADRATIC] [, /QUADRATIC] [, /SPLINE] )
For irregular grids: Result = INTERPOL( V, X, U [, /LSQUADRATIC] [, /QUADRATIC] [, /SPLINE] )
The result is a single- or double-precision floating-point vector, or a complex vector if the input vector is complex.
An input vector of any type except string.
The number of points in the result when both input and output grids are regular. The abscissa values for the output grid will contain the same endpoints as the input.
The abscissa values for V, in the irregularly-gridded case. X must have the same number of elements as V, and the values must be strictly ascending or descending.
The abscissa values for the result. The result will have the same number of elements as U. U does not need to be monotonic.
If set, interpolate using a least squares quadratic fit to the equation y = a + bx + cx2, for each 4 point neighborhood (x[i-1], x[i], x[i+1], x[i+2]) surrounding the interval of the interpolate, x[i] £ u < x[i+1].
If set, interpolate by fitting a quadratic y = a + bx + cx2, to the three point neighborhood (x[i-1], x[i], x[i+1]) surrounding the interval x[i] £ u < x[i+1].
If set, interpolate by fitting a cubic spline to the 4 point neighborhood (x[i-1], x[i], x[i+1], x[i+2]) surrounding the interval, x[i] £ u < x[i+1].
Create a floating-point vector of 61 elements in the range [-3, 3].
X = FINDGEN(61)/10 - 3 ; Evaluate V[x] at each point: V = SIN(X) ; Define X-values where interpolates are desired: U = [-2.50, -2.25, -1.85, -1.55, -1.20, -0.85, -0.50, -0.10, $ 0.30, 0.40, 0.75, 0.85, 1.05, 1.45, 1.85, 2.00, 2.25, 2.75 ] ; Interpolate: result = INTERPOL(V, X, U) ; Plot the function: PLOT, X, V ; Plot the interpolated values: OPLOT, U, result
BILINEAR, INTERPOLATE, KRIG2D