Plot a: NAC view of the Hapi region (0.37 m px⁻¹); this image was acquired in 2014. Plot b: close-up of a boulder and of its shadow. The green line represents the projection of the Sun illumination direction. Plot c: boulder section (we note the different scales on the plot axes deforming the boulder shape). The y-axis is oriented as the normal to the average plane around the peak of the shadow. The x-axis is obtained by projecting the green line in plot b on this average plane; the x-axis origin coincides with the peak of the shadow. We note that by comparing plots b and c, the shadow lengths appear different because of projection effects.