These functions implement bivariate interpolation onto a grid
for irregularly spaced input data. These functions are only for
backward compatibility, use interp instead.
interp.old(x, y, z, xo= seq(min(x), max(x), length = 40),
yo=seq(min(y), max(y), length = 40), ncp = 0,
extrap=FALSE, duplicate = "error", dupfun = NULL)
interp.new(x, y, z, xo = seq(min(x), max(x), length = 40),
yo = seq(min(y), max(y), length = 40), linear = FALSE,
ncp = NULL, extrap=FALSE, duplicate = "error", dupfun = NULL)vector of x-coordinates of data points or a
SpatialPointsDataFrame object.
Missing values are not accepted.
vector of y-coordinates of data points. Missing values are not accepted.
If left as NULL indicates that x should be a
SpatialPointsDataFrame and z names the variable of
interest in this dataframe.
vector of z-coordinates of data points or a character variable
naming the variable of interest in the
SpatialPointsDataFrame x.
Missing values are not accepted.
x, y, and z must be the same length
(execpt if x is a SpatialPointsDataFrame) and may
contain no fewer than four points. The points of x and
y cannot be collinear, i.e, they cannot fall on the same line
(two vectors x and y such that y = ax + b for
some a, b will not be accepted). interp is
meant for cases in which you have x, y values
scattered over a plane and a z value for each. If, instead,
you are trying to evaluate a mathematical function, or get a
graphical interpretation of relationships that can be described by a
polynomial, try outer().
vector of x-coordinates of output grid. The default is 40 points
evenly spaced over the range of x. If extrapolation is not being
used (extrap=FALSE, the default), xo should have a
range that is close to or inside of the range of x for the
results to be meaningful.
vector of y-coordinates of output grid; analogous to
xo, see above.
logical -- indicating wether linear or spline
interpolation should be used. supersedes old ncp parameter
deprecated, use parameter linear. Now only used by
interp.old().
old meaning was:
number of additional points to be used in computing partial
derivatives at each data point.
ncp must be either 0 (partial derivatives are not used), or at
least 2 but smaller than the number of data points (and smaller than
25).
logical flag: should extrapolation be used outside of the convex hull determined by the data points?
character string indicating how to handle duplicate data points. Possible values are
"error"produces an error message,
"strip"remove duplicate z values,
"mean","median","user"calculate
mean , median or user defined function (dupfun) of duplicate
z values.
a function, applied to duplicate points if
duplicate= "user".
list with 3 components:
vectors of x- and y- coordinates of output grid, the same as the input
argument xo, or yo, if present. Otherwise, their
default, a vector 40 points evenly spaced over the range of the
input x.
matrix of fitted z-values. The value z[i,j] is computed
at the x,y point xo[i], yo[j]. z has
dimensions length(xo) times length(yo).
If input is a SpatialPointsDataFrame a SpatialPixelssDataFrame is returned.
see interp
Akima, H. (1978). A Method of Bivariate Interpolation and Smooth Surface Fitting for Irregularly Distributed Data Points. ACM Transactions on Mathematical Software 4, 148-164.
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.
contour, image,
approx, spline,
aspline,
outer, expand.grid.