[R] interp function in package akima
dwinsemius at comcast.net
Mon Feb 8 23:58:21 CET 2010
On Feb 8, 2010, at 5:06 PM, Sacha Viquerat wrote:
> hello! does anyone know how to get values out of an interp object
> (from akima package)? ive constructed an elevation map and would
> like to numerically see the calculated z values of data points,
> which were not empirically sampled (basically: id like to see the
> altitude at locations x,y which have been computed by the interp
> function. is there any way? thanks in advance!
Have you read the help page for interp??? The interp function returns
a list, the third element of which is a matrix named "z":
interpFn <- interp( < arguments > )
interpFn$z # should return that matrix
If your pick out a particular element associated with the 10th x-value
and the 20th y-value, you should be able get the x,y,z triplet by
c(interpFn$x , interpFn$y ,interpFn$z[10,20] )
If you have particular x,y values you want to access then you need to
include them in the xo and yo vectors supplied to interp().
interp() does not provide interpolation between points on the output
grid, at least as as I read the help page.
There are strategies that could do so. Whenever I estimate a crossed-
spline model in package Design, I could extract a 2d-spline function
if I chose to.
David Winsemius, MD
West Hartford, CT
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