Example of a source for which the HOG method indicates a low morphological correlation and the Spearman correlation indicates a high correlation. The source is AG019.8843-0.5337 and in the comparison of the continuum and of the moment-0 of H₂CO 3_0,3−2_0,2 in the mask_ext. V_N=0.20, while ρ_s = 0.67. The two panels in the upper row show the continuum and the moment-0 map of H₂CO 3_0,3−2_0,2 with superimposed the directions of the gradients in the two maps (red: moment-0, white: continuum, respectively). The panel in the lower row shows the scatter plot of the pixel-to-pixel rank variables in the two maps inside the same mask (in black in the images of the two maps) where both the Spearman correlation and the Projected Rayleigh Statistic, V_N, have been computed.