[GRASS-dev] [GRASS GIS] #3468: r.drain: replace with new r.path, support multiple directions

[GRASS GIS]

#3468: r.drain: replace with new r.path, support multiple directions
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 Reporter:  mmetz        |      Owner:  grass-dev@…
     Type:  enhancement  |     Status:  new
 Priority:  normal       |  Milestone:  7.5.0
Component:  Raster       |    Version:  svn-releasebranch74
 Keywords:  r.drain      |        CPU:  All
 Platform:  All          |
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 r.drain is a clone of r.fill.dir, with the added functionality to extract
 a path from a given start point to the nearest outlet, using internally
 calculated directions. Later on, the option to supply a direction map was
 added in order to support output from r.cost, r.walk, and r.watershed.
 This code duplication should be avoided. A new module r.path could be
 added that uses a direction map with optional surface map to trace paths.
 r.drain could then be converted to a script calling r.path. If no
 direction map is supplied, r.fill.dir can be used by r.drain to create a
 direction map.

 r.fill.dir uses a bitmask to encode multiple directions from a single
 cell, as described by Jenson and Domingue (1988). These multiple
 directions are internally resolved to find the main (single) flow
 direction which is then recoded to a standard direction format using
 degrees. This bitmask to encode multiple directions from a single cell
 could be used and exposed by various other modules, i.e. r.cost, r.walk,
 r.watershed, to be used as input for r.path. As a result, the least costly
 path from a single start point to a single stop point can split and merge
 repeatedly (see attached multiple-directions-path.png).

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Ticket URL: <https://trac.osgeo.org/grass/ticket/3468>
GRASS GIS <https://grass.osgeo.org>