Distribution of line centroids in the position-position-velocity space for ¹³CO (left) and C¹⁸O (right). The colours vary with velocity to help the 3D visualisation. The black points are projections of the colour ones on the faces of the box. In the right frame, lines joining the projections to the colour points are drawn to help visualising in 3D the positions of s1454 (in the north clump), s1461 (at the root of the north-eastern filament), s1446 (in the arc), and s1453 (just north to the arc).