At least one output map is required:
r.mapcalc scheidegger=shreve*2
The algorithm is very similar to Strahler's algorithm, it proceeds downstream,
and at every node the stream magnitude is the sum of its tributaries.
Module can work only if direction map, stream map and region map has same settings. It is also required that stream map and direction map come from the same source. For lots of reason this limitation probably cannot be omitted. This means if stream map comes from r.stream.extract also direction map from r.stream.extract must be used. If stream network was generated with MFD method also MFD direction map must be used. Nowadays f direction map comes from r.stream.extract must be patched by direction map from r.watershed. (with r.patch).
Horton, R. E. (1945), Erosional development of streams and their drainage basins: hydro-physical approach to quantitative morphology, Geological Society of America Bulletin 56 (3): 275-370
Shreve, R., Statistical Law of Stream Numbers, J. Geol., 74, (1966), 17-37.
Strahler, A. N. (1952), Hypsometric (area-altitude) analysis of erosional topology, Geological Society of America Bulletin 63 (11): 1117–1142
Strahler, A. N. (1957), Quantitative analysis of watershed geomorphology, Transactions of the American Geophysical Union 8 (6): 913–920.
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