RFGLS_estimate_spatial
                        Function for estimation in spatial data with
                        RF-GLS
RFGLS_estimate_timeseries
                        Function for estimation in time-series data
                        with RF-GLS
RFGLS_predict           Prediction of mean function with RF-GLS
RFGLS_predict_spatial   Spatial response prediction at new location
                        with RF-GLS
