Maps expressing directions may use different conventions according to the field of study they are used in. The "GRASS" convention is 'theta CCW from the +x axis' (i.e. mathematical|Cartesian convention), which means CCW from E and pointing to the direction (aspect, flow), whereas for example when dealing with meteorological data, wind is usually expressed CW from N and pointing from where wind blows. Some modules currently adopt different angle conventions, therefore it is always necessary to be aware of which convention the direction maps are expressed in. See also
Pages in category "Angle Conventions"
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