Performs a local 1D-optimal interpolation (objective analysis).
Every elements in f corresponds to a data point (observation) at location x,y with the error variance var.
lenx is correlation length in x-direction. m represents the number of influential points.
xi is the data points where the field is interpolated. fi is the interpolated field and vari is its error variance.
The background field of the optimal interpolation is zero. For a different background field, the background field must be subtracted from the observation, the difference is mapped by OI onto the background grid and finally the background is added back to the interpolated field.
Package: optiminterp