Note: This document is for an older version of GRASS GIS that will be discontinued soon. You should upgrade, and read the current manual page.
NAME
d.rast.arrow - Draws arrows representing cell aspect direction for a raster map containing aspect data.
KEYWORDS
display,
map annotations,
raster,
arrow
SYNOPSIS
d.rast.arrow
d.rast.arrow --help
d.rast.arrow [-a] map=name [type=string] [color=name] [grid_color=name] [null_color=name] [unknown_color=name] [skip=integer] [magnitude_map=string] [scale=float] [--help] [--verbose] [--quiet] [--ui]
Flags:
- -a
- Align grids with raster cells
- --help
- Print usage summary
- --verbose
- Verbose module output
- --quiet
- Quiet module output
- --ui
- Force launching GUI dialog
Parameters:
- map=name [required]
- Name of raster aspect map to be displayed
- type=string
- Type of existing raster aspect map
- Options: grass, compass, drainage, agnps, answers
- Default: grass
- color=name
- Color for drawing arrows
- Either a standard color name or R:G:B triplet
- Default: green
- grid_color=name
- Color for drawing drawing grid
- Either a standard color name, R:G:B triplet, or "none"
- Default: gray
- null_color=name
- Color for drawing null values (X symbol)
- Either a standard color name, R:G:B triplet, or "none"
- Default: black
- unknown_color=name
- Color for showing unknown information (? symbol)
- Either a standard color name, R:G:B triplet, or "none"
- Default: red
- skip=integer
- Draw arrow every Nth grid cell
- Default: 1
- magnitude_map=string
- Raster map containing values used for arrow length
- scale=float
- Scale factor for arrows (magnitude map)
- Default: 1.0
d.rast.arrow
is designed to help users better visualize surface water flow direction,
as indicated in an aspect raster map layer. There are two ways to specify
the aspect layer the program is to use. The first is to display the aspect
map layer on the graphics monitor before running
d.rast.arrow.
The second method involves setting the
map parameter
to the name of the desired aspect map.
This allows the arrows to be drawn over any other maps already displayed
on the graphics monitor.
d.rast.arrow will draw an arrow over each displayed cell
to indicate in which direction the cell slopes. If the aspect
layer has a category value denoting locations of "unknown" aspect,
d.rast.arrow draws a question mark over the displayed cells
of that category.
Cells containing null data will be marked with an "X".
You can disable drawing of null data and unknown aspect values by
setting its color to "none".
When specifying the magnitude_map option, arrow lengths
denoting magnitude will be extracted from the cell values of the specified
map. In this case the tail of the arrow will be centered on the source cell.
You may adjust the overall scale using the scale option.
d.rast.arrow will ignore NULL and negative magnitudes, and will
warn you if the debug level is set at 5 or higher. Be aware. If your application
uses negative values for magnitude, you can use
r.mapcalc to prepare the magnitude map to
suit your needs (absolute value, inverted direction and so on).
By default, arrows are drawn at the size of a cell and cannot be seen if
the raster map is relatively close in scale. You can use the
skip
option to draw arrows every n-th cell in both directions if you are working
with relatively high resolutions. It may be useful to disable the grid in
this case, which is accomplished by setting its color to "
none".
For GRASS and Compass type aspect maps, the cell values of the aspect map
will determine the corresponding direction in 360 degrees. ANSWERS type aspect
maps will be plotted in multiples of 15 degrees counterclockwise from east, and
AGNPS and Drainage type aspect maps will be displayed in D8 representation,
i.e. the eight multiples of 45 degrees. Cell values are 1 to 8 clockwise from
north for AGNPS and 1 to 8 counterclockwise from north east for Drainage. See
r.watershed for more details about the
Drainage aspect.
GRASS aspect maps are measured using Cartesian conventions, i.e. in degrees
counterclockwise from east. e.g.:
90 North
180 West
270 South
0,360 East
They can be created from a raster elevation map with
r.slope.aspect.
Compass type aspect maps are measured in degrees clockwise from north.
This module uses oceanographic conventions, i.e. arrows point downslope or
direction "to", as opposed to atmospheric conventions (direction "from").
Convert U,V velocity component maps into magnitude,direction maps for use
with
d.rast.arrow:
r.mapcalc "magnitude = sqrt(U_map^2 + V_map^2)"
r.mapcalc "direction = atan(U_map, V_map)"
d.rast.arrow map=direction type=grass magnitude_map=magnitude skip=3 grid=none
Sea wind speed (magnitude) and direction shown in the Tasmanian Sea
d.frame,
d.rast,
d.rast.edit,
d.rast.num,
g.region,
r.slope.aspect,
r.watershed
Original author
Chris Rewerts
Agricultural Engineering,
Purdue University
Magnitude and 360 arrow code
Hamish Bowman
Department of Marine Science,
University of Otago, New Zealand
Align grids with raster cells and Drainage aspect type
Huidae Cho
SOURCE CODE
Available at:
d.rast.arrow source code
(history)
Latest change: Thursday Dec 22 10:46:08 2022 in commit: 8de925f87be22a5c943f2969a2872a288d72f2f7
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© 2003-2024
GRASS Development Team,
GRASS GIS 8.3.3dev Reference Manual