Top left: PFSS magnetic rendering corresponding to the filament region rendered by PFSS for Sept. 29 data. A low-resolution magnetogram was used, with the same FOV as Fig. 1 (right). Top right: transverse slice of the decay index n across the volume that encloses the filament and emergence. The estimated height of the filament for Sept. 29 is marked with a black cross (corrected), or small circumference (uncorrected). Bottom: longitudinal slice of the decay index n along the volume that encloses the filament and emergence, and same symbols for the filament height. This figure belongs to Sect. 2.3.