Both from the code and the error message it appears that you are
creating character matrices and unrealistically expecting a function
designed for numeric input to accept those as arguments.
?sprintf
It appears you are hoping that sprintf gets you something you desire,
but to my eyes it looks entirely troublesome in this application. You
should be able to report which line of code is provoking the error.
I'm guessing it is:
loc <- make.surface.grid(list(x=a.mat, y=b.mat))
What happens when you just use numeric arguments?
--
David.
On Jun 21, 2009, at 1:33 PM, Andrew Aldersley wrote:
Dear all,
I'm having trouble interpolating a number of gridded datasets that I
have. I'm quite new to R so any help/advice that can be offered
would be much appreciated!
Firstly I'll describe my dataset. The data is a grid of the planet
at 1 degree spatial resolution, with each grid cell containing a
value describing a particular variable (e.g. population density) for
coordinate pairs. The dimensions of the grid are 360col x 180row.
The x-coordinates of the values within the grid are longitudes (from
-179.5(W) to 179.5(E)) and the y-coordinates of the grid values are
latitudes (from 89.5(N) to -89.5(S)).
What I want to do is convert this 1 degree dataset to a finer
resolution of 0.5 degrees, thereby quadrupling the number of cells
within the frame (i.e. convert to 720 x 360 grid). I wish to have
longitudinal values ranging from -179.75 to 179.75 and latitudinal
values from 89.75 to -89.75. I selected the 'interp.surface'
function in the 'fields' package to do this as it provides bilinear
interpolation from one grid to another. I have written the following
code to try and carry out my interpolation...
library(fields)
x.mat <- sprintf("%.2f", seq(from = -179.5, to = 179.5,
length=360)) # longitude grid values
y.mat <- sprintf("%.2f", seq(from = 89.5, to = -89.5, length=180))
# latitude grid values
z.mat <- read.table("BF_200501.txt", colClasses="numeric") # dataset
z.mat <- data.matrix(z.mat)
obj <- list(x=x.mat, y=y.mat, z=z.mat)
#Setting up new grid
a.mat <- sprintf("%.2f", seq(from = -179.75, to = 179.75, length =
720)) # longitude grid values
b.mat <- sprintf("%.2f", seq(from = 89.75, to = -89.75, length =
360)) # latitude grid values
loc <- make.surface.grid(list(x=a.mat, y=b.mat))
#Interpolation
new <- interp.surface(obj, loc)
However I get the following error message:
Error in x.new - min(x) : non-numeric argument to binary operator
Can anyone explain what this error message means and why I am
getting it? Or are there other more effective ways to perform the
interpolation on this sort of dataset? Like I said I'm new to R so
any advice will be gratefully received.
Many thanks,
Andy
David Winsemius, MD
Heritage Laboratories
West Hartford, CT
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