C¹⁸O (1–0) PPV space in the velocity interval of 30–44 km s⁻¹. The projections on the three axes are presented. The colour of each point represents the centroid velocity at that point, corresponding to the colour bar shown to the right of the panel. The symbols ‘Xs’ are similar to those in Fig. 1, and the W33 complex is marked by the black dashed lines or the dashed ellipses on the three projections.