Sketch of the subsequent longitudinal accretion of the filament S242. The overlaid green contours display ¹³CO column density distribution of filament S242, ranging from 15 to 90% stepped by 15% of the value (1.5 × 10¹⁶ cm⁻²). The skeleton structures of the filament S242 are color-coded by the longitudinal factor f_L, which is the contribution of longitudinal collapse for the observed velocity dispersion. The magenta arrows indicate the direction of gas motion in longitudinal collapse and accretion, the blue arrows in radial collapse. The right subpanel presents the profile of longitudinal factor f_L along the spine of filament S242.