Histogram of relative orientation between the RHT angle expectation value (RHT-H case) and the direction angle derived from the GRAD method (GRAD-L case) for Region 1 (top) and Region 2 (bottom). The angles were calculated for the pixels that are common to both methods (yellow areas in Figs. 2 and 3). The curves show the HROs for three column-density bins: the highest and lowest ones (red and black, respectively) and the intermediate bin between these two (blue). A ± 1 σ error is represented by the width of the shaded areas.