R: Bivariate Interpolation for Data on a Rectangular grid

bicubic {interp} | R Documentation

## Bivariate Interpolation for Data on a Rectangular grid

### Description

This is a placeholder function for backward compatibility with packaga akima.

In its current state it simply calls the reimplemented Akima algorithm for irregular grids applied to the regular gridded data given.

Later a reimplementation of the original algorithm for regular grids may follow.

### Usage

    bicubic(x, y, z, x0, y0)

### Arguments

`x` | a vector containing the `x` coordinates of the rectangular data grid.
`y` | a vector containing the `y` coordinates of the rectangular data grid.
`z` | a matrix containing the `z[i,j]` data values for the grid points (`x[i]`,`y[j]`).
`x0` | vector of `x` coordinates used to interpolate at.
`y0` | vector of `y` coordinates used to interpolate at.

### Details

This function is a call wrapper for backward compatibility with package akima.

Currently it applies Akimas irregular grid splines to regular grids, later a FOSS reimplementation of his regular grid splines may replace this wrapper.

### Value

This function produces a list of interpolated points:

`x` | vector of `x` coordinates.
`y` | vector of `y` coordinates.
`z` | vector of interpolated data `z`.

If you need an output grid, see `bicubic.grid`.

### Note

Use `interp` for the general case of irregular gridded data!

### References

Akima, H. (1996) Rectangular-Grid-Data Surface Fitting that Has the Accuracy of a Bicubic Polynomial, J. ACM 22(3), 357-361

### See Also

`interp`, `bicubic.grid`

### Examples

    data(akima474)
    # interpolate at the diagonal of the grid [0,8]x[0,10]
    akima.bic <- bicubic(akima474$x,akima474$y,akima474$z,
                         seq(0,8,length=50), seq(0,10,length=50))
    plot(sqrt(akima.bic$x^2+akima.bic$y^2), akima.bic$z, type="l")

[Package interp version 1.1-1 Index]