R: Bicubic Interpolation for Data on a Rectangular grid

bicubic.grid {interp} | R Documentation

## Bicubic 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.grid(x,y,z,xlim=c(min(x),max(x)),ylim=c(min(y),max(y)),
                 nx=40,ny=40,dx=NULL,dy=NULL)

### 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]`).
`xlim` | vector of length 2 giving lower and upper limit for range `x` coordinates used for output grid.
`ylim` | vector of length 2 giving lower and upper limit for range of `y` coordinates used for output grid.
`nx` | output grid dimension in `x` direction.
`ny` | output grid dimension in `y` direction.
`dx` | output grid spacing in `x` direction, not used by default, overrides `nx` if specified.
`dy` | output grid spacing in `y` direction, not used by default, overrides `ny` if specified..

### 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 grid of interpolated points, feasible to be used directly with `image` and `contour`:

`x` | vector of `x` coordinates of the output grid.
`y` | vector of `y` coordinates of the output grid.
`z` | matrix of interpolated data for the output 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`

### Examples

    data(akima474)
    # interpolate at a grid [0,8]x[0,10]
    akima.bic <- bicubic.grid(akima474$x,akima474$y,akima474$z)
    zmin <- min(akima.bic$z, na.rm=TRUE)
    zmax <- max(akima.bic$z, na.rm=TRUE)
    breaks <- pretty(c(zmin,zmax),10)
    colors <- heat.colors(length(breaks)-1)
    image(akima.bic, breaks=breaks, col=colors)
    contour(akima.bic, levels=breaks,  add=TRUE)

[Package interp version 1.1-1 Index]