[GRASS-dev] [GRASS GIS] #3468: r.drain: replace with new r.path, support multiple directions
GRASS GIS
trac at osgeo.org
Wed Dec 20 02:07:18 PST 2017
#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
Resolution: | Keywords: r.drain
CPU: All | Platform: All
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Comment (by mlennert):
Replying to [ticket:3468 mmetz]:
> 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.
+1
>
> 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).
+1
;-)
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Ticket URL: <https://trac.osgeo.org/grass/ticket/3468#comment:1>
GRASS GIS <https://grass.osgeo.org>
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