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

[GRASS GIS]

#2637: Get direction raster in clockwise degrees starting from the North
-------------------------+--------------------------------------------------
 Reporter:  cgravelm     |       Owner:  grass-dev@…              
     Type:  enhancement  |      Status:  new                      
 Priority:  normal       |   Milestone:  7.0.1                    
Component:  Raster       |     Version:  7.0.0                    
 Keywords:               |    Platform:  MacOSX                   
      Cpu:  Unspecified  |  
-------------------------+--------------------------------------------------

Comment(by neteler):

 Replying to [comment:1 annakrat]:
 > You can just use r.mapcalc "angle_cw = -angle_ccw + 450", this will give
 you what you need. It outputs angles from 90 to 450, but that's typically
 not a problem.

 ... or you solve it with an if() condition.

 Shell script solution:

 {{{
 rotate_angle()
 {
  is_negative=`echo "$1" | awk '{printf "%d\n", $1 < 0. ? 1 : 0}'`

  if [ $is_negative -eq 0 ] ; then
    tmp=`echo "$1"   | awk '{printf "%f\n", 360. - $1 + 90.}'`
    tmp=`echo "$tmp" | awk '{printf "%f\n", $1 >= 360. ? $1 - 360. : $1}'`
    echo "$tmp"
  else
    echo "NA"
  fi
 }

 rotate_angle 270
 #[1] 180
 rotate_angle 180
 #[1] 270
 }}}

 Likewise you could use r.mapcalc and its eval() function.

 > I guess it could be implemented in r.slope.aspect.

 Note the (old) patch:

 raster/r.slope.aspect/r_sl_asp_northangle_diffs.tar.gz

 Important: the output of r.slope.aspect can be used as input elsewhere,
 hence a flag would increase the risk to mess up subsequent calculations.

-- 
Ticket URL: <http://trac.osgeo.org/grass/ticket/2637#comment:3>
GRASS GIS <http://grass.osgeo.org>