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List: grass-dev
Subject: Re: [GRASS-dev] [GRASS GIS] #2637: Get direction raster in clockwise degrees starting from the North
From: "GRASS GIS" <trac () osgeo ! org>
Date: 2015-03-27 17:46:58
Message-ID: 051.c07faf5fe626fef64fedd4978ba64759 () osgeo ! org
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#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.
--
Ticket URL: <http://trac.osgeo.org/grass/ticket/2637#comment:8>
GRASS GIS <http://grass.osgeo.org>
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