[GRASS-dev] [GRASS GIS] #2637: Get direction raster in clockwise degrees starting from the North

GRASS GIS trac at osgeo.org
Mon Jan 29 01:38:38 PST 2018

#2637: Get direction raster in clockwise degrees starting from the North
  Reporter:  cgravelm     |      Owner:  grass-dev@…
      Type:  enhancement  |     Status:  new
  Priority:  normal       |  Milestone:  7.4.1
 Component:  Raster       |    Version:  7.0.0
Resolution:               |   Keywords:
       CPU:  Unspecified  |   Platform:  MacOSX

Comment (by hellik):

 Replying to [comment:22 mmetz]:
 > Replying to [comment:21 cmbarton]:
 > > Such a flag would still be useful for a variety of applications and
 should not interfere with other modules if the default behavior remains
 the same.
 > Such a flag would be easy to implement, but a clear definition of aspect
 with regard to zero or small slope is currently missing. Generally, for
 zero slope, zero aspect is produced, i.e. a value of zero does not mean
 East, but zero slope, while East is encoded as 360 degrees. However, if
 min_slope is > 0 and slope < min_slope, slope is set to zero, but aspect
 is set to NULL. This is not consistent. Therefore I suggest to produce
 zero aspect for zero slope or if slope is < min_slope. NULL is then
 reserved for those cells where slope and aspect can not be computed. This
 also means that when converting CCW from East to CW from North, North must
 be encoded as 360 degrees, not 0 degrees.

 sounds reasonable.

Ticket URL: <https://trac.osgeo.org/grass/ticket/2637#comment:23>
GRASS GIS <https://grass.osgeo.org>

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