[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
--------------------------+---------------------------------
  Reporter:  mmetz        |      Owner:  grass-dev@…
      Type:  enhancement  |     Status:  new
  Priority:  normal       |  Milestone:  7.5.0
 Component:  Raster       |    Version:  svn-releasebranch74
Resolution:               |   Keywords:  r.drain
       CPU:  All          |   Platform:  All
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Comment (by mmetz):

 Replying to [comment:2 wenzeslaus]:
 > Replying to [ticket:3468 mmetz]:
 [...]
 >
 > Once r.drain is a script, it would be great if we can manage to also
 remove the need for providing a "dummy" cost map. See `r.mapcalc "const1 =
 1"` in a r.drain example I created recently (please, correct me if I'm
 wrong):
 >
 > https://grass.osgeo.org/grass74/manuals/r.drain.html#path-following-
 directions

 Yes, a dummy cost map should not be needed. Either an elevation map or a
 direction map is needed. If a direction map is not provided, an elevation
 map will be needed to create a direction map with r.fill.dir.
 >
 > Jenson and Domingue (1988) is a format described in a paper and it makes
 sense adding it. Any ideas for a name? The current ones (in r.fill.dir)
 are not really descriptive (agnps, answers, grass).

 I suggest bitmask as a new name. This name is also not really descriptive
 and should be explained in the manual of r.fill.dir. BTW, the manual of
 r.fill.dir provides clear explanations of
 agnps, answers, grass.
 >
 > > i.e. r.cost, r.walk, r.watershed, to be used as input for r.path.
 >
 > One common format for all modules would be great.

 Two common formats: 1. degrees CCW from East, 2. bitmask for multiple
 directions as described by Jenson and Domingue (1988)
 > It is strange when user needs to recompute the angles like in my r.drain
 example from above (again, correct me if I'm wrong):
 >
 > https://grass.osgeo.org/grass74/manuals/r.drain.html#path-following-
 directions

 That would be a substantial change because other modules (all r.stream.*)
 depend on the direction output of r.watershed.
 >
 > > 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).
 >
 > Looks great!

 Implemented in r71962 (added r.path) and r71963 (updated r.cost/r.walk).

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Ticket URL: <https://trac.osgeo.org/grass/ticket/3468#comment:3>
GRASS GIS <https://grass.osgeo.org>