OS: Windows XP SP2
When I use the interp.surface() function, on occasion I have encountered
the following error message:
Error in interp.surface(a, loc) : subscript out of bounds
Since it is somewhat dependent on the data set, I cannot say exactly in
which cases these occur, but I believe I have found the problem and a
solution for it:
The scaling calculations in the code,
lx <- ((nx - 1) * (loc[, 1] - xa))/xr + 1
ly <- ((ny - 1) * (loc[, 2] - ya))/yr + 1
can lead to numerical error, so in the following lines
lx1 <- ifelse(lx == nx, nx - 1, trunc(lx))
ly1 <- ifelse(ly == ny, ny - 1, trunc(ly))
the equality statements which are the first arguments to the IF-ELSE
statements return false when they are supposed to be true. I believe the
remedy is to simply avoid absolute equalities, as in the following example
(which has worked for my problem):
lx1 <- ifelse(abs(lx - nx) < 1e-10, nx - 1, trunc(lx))
ly1 <- ifelse(abs(ly - ny) < 1e-10, ny - 1, trunc(ly))
I hope this is an appropriate posting for an error report. Thank you very
much for your hard work,
I think
ifelse(lx >= nx, nx - 1, trunc(lx))
ifelse(ly >= ny, ny - 1, trunc(ly))
would probably be a better fix, but I'd really like to see an example
of this in action. Could you email me a dataset where you see it?
Duncan Murdoch