I have a little doubt about the way I should calculate the value of the "scale" parameter in the r.relief command in GRASS.
In the description section of the r.relief page of the GRASS manual I read: "The scaling parameter, which compensates for a different horizontal scale than vertical scale. If scale is a number, then the ewres and nsres are multiplied by that scale to calculate the shading. (Default=1.0 for equivalent horizontal and vertical scales.)" while in the parameters section of the same page I read: "Scale factor for converting meters to elevation units". This last statement is confusing to me because it seems to contradict the previous one in my opinion.
I'm working with ASTER GDEM v2, so if I'm not wrong I should change the default value because horizontal scale is defined in degrees while vertical scale is defined in meters.
Now, what's the right value for the "scale" parameter? Is it the number of vertical scale units (meters in my case) contained in the horizontal scale unit (degree in my case)? Is it vice versa (the number of horizontal scale units contained in the vertical scale unit?) Or is it simply the default value because the vertical scale is defined in meters ("Scale factor for converting meters to elevation units")?