[GRASS-dev] [GRASS GIS] #2637: Get direction raster in clockwise degrees starting from the North
GRASS GIS
trac at osgeo.org
Sun Jan 28 22:27:45 PST 2018
#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: 7.4.1
Component: Raster | Version: 7.0.0
Resolution: | Keywords:
CPU: Unspecified | Platform: MacOSX
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Comment (by 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.
Note that in r.slope.aspect there is the choice of outputting slope as
degrees or percent, with degrees being the default.
Just because outputting direction as in a compass bearing is not useful
for some people does not mean that it would not be useful for other. For
anyone interested in knowing what compass direction a location is facing
(and that is a question that people have), the current output is
completely misleading.
The manual states "The aspect output raster map indicates the direction
that slopes are facing". To most people, the word "direction" refers to a
compass direction = azimuth. If they keep reading, it gets increasingly
baffling from this point of view. "The aspect categories represent the
number degrees of east. Category and color table files are also generated
for the aspect raster map. The aspect categories represent the number
degrees of east and they increase counterclockwise: 90 degrees is North,
180 is West, 270 is South 360 is East."
I understand the history of this (from before GRASS rasters were
georegistered) and realize that because of this long legacy effect, other
raster modules have been written to expect this kind of non-cartographic
direction metric. But a simple flag to let users change this to represent
what a map direction is commonly expected to mean seems like a useful
enhancement.
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Ticket URL: <https://trac.osgeo.org/grass/ticket/2637#comment:21>
GRASS GIS <https://grass.osgeo.org>
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