Good question; the meuse example does not explain how to get meuse.grid.
The asciigrid file you have you should read with readGDAL in package
rgdal, if that goes wrong I'd expect the problem in your data file.
Otherwise, if you have a shapefile with a polygon covering the
catchment, called catch.pol, you'd want to use
sel = overlay(catch.pol, catch.grid)
The grid cells inside the polygon(s) are now found by
catch.sel = catch.grid[!is.na(sel)]
--
Edzer
Mauricio Zambrano wrote:
Dear List,
My question is about how to define the grid to be used for the
interpolations, using R 2.7.0 and gstat 0.9-47
I'm working in a catchment of ~3000 km2, with daily rainfall data of
several stations (more than 40), and I would like to interpolate daily
values within all the catchment using ordinary Kriging.
For defining the grid in which the interpolation will be carried out,
at the beginning, I tried with
#setting a grid each 100m vertical and horizontal
dx <- seq(674400,730700,by=100)
dy <- seq(4615100,4744400,by=100)
catch.grid <- expand.grid(dx,dy)
#setting the names of the columns of the grid
names(catch.grid) <- c("x","y")
#setting the coordinates of the grid
coordinates(catch.grid) <- ~x+y
#interpolating with the inverse distance
pp.idw <- krige(PP_DAILY_MEAN_MM~1, meteo_catch_nNA, catch.grid)
#plotting the interpolated values
spplot(pp.idw["var1.pred"], main="Daily Mean PP, [mm]")
but looking at the figure I realized that the interpolations were
carried out considering all the cells within the squared grid, and not
only within the catchment.
After, I tried reading a raster file (each 100m) and using it as the grid,
DEMM100m <- read.asciigrid("Catch_DEM_c100m")
but the results that I got seems to be wrong, because I got high
values where low values were expected and viceversa. (I really
appreciate any help clarifying me what I'm doing wrong )
Is there any way to define a grid, starting from a shapefile of the
catchment boundaries ?. For example, I would like to define something
similar to the "meuse.grid" dataset.
Thanks in advance and best regards
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