[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
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 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  |  
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Comment(by cmbarton):

 Replying to [comment:7 cmbarton]:
 > Thanks for the simple mapcalc approach. I think, however, the point is
 not that this cannot be calculated in mapcalc. It is that it would be
 convenient to have the primary aspect module for GRASS have an option to
 calculate aspect in cardinal degrees from north, what most users would
 expect from an aspect calculation in a GIS. The counter clockwise from E.
 is a path dependent legacy from the early days of GIS when rasters were
 treated like a 2D graph. Other modules have come to expect that, which is
 OK. Perhaps it even makes some math easier in some uses. But we no longer
 calculate raster cell position from the lower left. So it is odd that
 r.slope.aspect does not at least have an option to treat aspect like a
 geographic value instead of only like a vector angle on a graph.

 The other thing is that all the mapcalc solutions require 2 passes through
 a map to get aspect as degrees from north. If this were a flag in
 r.slope.aspect, it could be done in 1 pass. This is important if you are
 doing a lot of big maps.

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Ticket URL: <http://trac.osgeo.org/grass/ticket/2637#comment:8>
GRASS GIS <http://grass.osgeo.org>