Defining a grid for interpolations ?

Mauricio Zambrano wrote:

Dear Paul and Edzer,

Thanks a lot for your answers.

Before reading the solution proposed by Paul, I had tried with:

# reading the boundary of the catchment
library(maptools)
catchment <- readShapePoly("only_catchment.shp")
catchment.grid <- spsample(catchment, cellsize=100, offset = c(0.5,
0.5)) # reading the boundary of the catchment

 and then I did an IDW interpolation with:

pp.idw <- krige(PP_DAILY_MEAN_MM~1, meteo, catchment.grid)

and it works.

However, after reading your solution, I realised that I didn't use the
command:

gridded(catchment.grid)

but I got an interpolation anyway.

Where is performed the interpolation when I don't use a gridded grid (
gridded(catchment.grid) ) ?

it is actually

gridded(catchment.grid) <- TRUE

that changes the object, if it not gridded.

For interpolation, it doesn't matter whether you loop over a set of points,
or a set of points on a grid.

--
Edzer