Addition of all position-velocity diagrams obtained along all the axes in the east-west direction. Above we show the result obtained for ¹²CO J = 3−2 emission, below the result for the ¹³CO line emission. (The color scale for ¹³CO is adapted to emphasize the weaker inner ring.) In the right bottom corner of both boxes two little rectangles are plotted to show spatial and spectral resolutions: along the Y-axis the larger rectangle (on the left) shows the beam size (0.17′′), the little rectangle (on the right) the pointing precision (0.01′′); along the X-axis their dimension correspond to the data spectral resolution (0.2 km s^-1). See Sect. 6 for more details.