fBasics (version 3011.87)

akimaInterp: Bivariate Spline Interpolation

Description

Interpolates bivariate data sets using Akima spline interpolation.

Usage

akimaInterp(x, y = NULL, z = NULL, gridPoints = 21,
    xo = seq(min(x), max(x), length = gridPoints),
    yo = seq(min(y), max(y), length = gridPoints), extrap = FALSE)
    
akimaInterpp(x, y = NULL, z = NULL, xo, yo, extrap = FALSE)

Arguments

x, y, z

for akimaInterp the arguments x and y are two numeric vectors of grid pounts, and z is a numeric matrix or any other rectangular object which can be transformed by the function

gridPoints

an integer value specifying the number of grid points in x and y direction.

xo, yo

for akimaInterp two numeric vectors of data points spanning the grid, and for akimaInterpp two numeric vectors of data points building pairs for pointwise interpolation.

extrap

a logical, if TRUE then the data points are extrapolated.

Value

• akimaInterp returns a list with at least three entries, x, y and z. Note, that the returned values, can be directly used by the persp and contour 3D plotting methods. akimaInterpp returns a data.frame with columns "x", "y", and "z".

Details

Two options are available gridded and pointwise interpolation. akimaInterp is a function wrapper to the interp function provided by the contributed R package akima. The Fortran code of the Akima spline interpolation routine was written by H. Akima. Linear surface fitting and krige surface fitting are provided by the functions linearInterp and krigeInterp.

References

Akima H., 1978, A Method of Bivariate Interpolation and Smooth Surface Fitting for Irregularly Distributed Data Points, ACM Transactions on Mathematical Software 4, 149-164.

Akima H., 1996, Algorithm 761: Scattered-Data Surface Fitting that has the Accuracy of a Cubic Polynomial, ACM Transactions on Mathematical Software 22, 362-371.

See Also

linearInterp, krigeInterp.

Examples

## akimaInterp -
   # Akima Interpolation:    
   if (require(akima)) {
     set.seed(1953)
     x = runif(999) - 0.5
     y = runif(999) - 0.5
     z = cos(2*pi*(x^2+y^2))
     ans = akimaInterp(x, y, z, gridPoints = 41, extrap = FALSE)
     persp(ans, theta = -40, phi = 30, col = "steelblue",
        xlab = "x", ylab = "y", zlab = "z")
     contour(ans)
   }