| akimaInterp {fBasics} | R Documentation |
Interpolates bivariate data sets using Akima spline interpolation.
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)
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 as.matrix into a matrix object.
For akimaInterpp we consider either three numeric vectors
of equal length or if y and z are NULL, a list with
entries x, y, z, or named data frame with
x in the first, y in the second, and z in
the third column.
|
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.
|
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.
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".
IMPORTANT: The contributed package akima is not in the
dependence list of the DESCRIPTION file due to license conditions.
The Rmetrics user has to load this package from the CRAN server on
his own responsibility, please check the license conditions.
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.
## 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)
}