Hi Peter, The curv_to_rect_map function computes the mapping function, which does store information using all four dimensions: the original X and Y dimensions represent the output longitude, latitude grid, and Z and T directions are used to save information about four neighbors (hence K=1:4) and the indices of the input longitude and latitude grids are saved using the T dimension. This is described a bit more near the end the documentation of the curv_to_rec_map function, where it says "The weights are based on the distance..." Your odd result is I think because the lon,lat curvilinear coordinate variables must be on the same 2D grid of index values as the variable you are regridding, but you have read them in as 1dimensional variables. Lon and lat should have the same grid as prec[d=2], so that you could make a curvilinear plot using a command like fill prec[d=2], lon, lat and then you could regrid prec[d=2] to a rectilinear grid using the two functions curv_to_rect_map and curv_to_rect. Ansley Peter Szabo wrote:
