1d.rast.arrow(1) GRASS GIS User's Manual d.rast.arrow(1)
2
6 d.rast.arrow - Draws arrows representing cell aspect direction for a
7 raster map containing aspect data.
8
10 display, map annotations, raster, arrow
11
13 d.rast.arrow
14 d.rast.arrow --help
15 d.rast.arrow [-a] map=name [type=string] [color=name]
16 [grid_color=name] [null_color=name] [unknown_color=name]
17 [skip=integer] [magnitude_map=string] [scale=float] [--help]
18 [--verbose] [--quiet] [--ui]
19 Flags:
21 -a
22 Align grids with raster cells
23 --help
25 Print usage summary
26 --verbose
28 Verbose module output
29 --quiet
31 Quiet module output
32 --ui
34 Force launching GUI dialog
35 Parameters:
37 map=name [required]
38 Name of raster aspect map to be displayed
39 type=string
41 Type of existing raster aspect map
42 Options: grass, compass, drainage, agnps, answers
43 Default: grass
44 color=name
46 Color for drawing arrows
47 Either a standard color name or R:G:B triplet
48 Default: green
49 grid_color=name
51 Color for drawing drawing grid
52 Either a standard color name, R:G:B triplet, or "none"
53 Default: gray
54 null_color=name
56 Color for drawing null values (X symbol)
57 Either a standard color name, R:G:B triplet, or "none"
58 Default: black
59 unknown_color=name
61 Color for showing unknown information (? symbol)
62 Either a standard color name, R:G:B triplet, or "none"
63 Default: red
64 skip=integer
66 Draw arrow every Nth grid cell
67 Default: 1
68 magnitude_map=string
70 Raster map containing values used for arrow length
71 scale=float
73 Scale factor for arrows (magnitude map)
74 Default: 1.0
75
77 d.rast.arrow is designed to help users better visualize surface water
78 flow direction, as indicated in an aspect raster map layer. There are
79 two ways to specify the aspect layer the program is to use. The first
80 is to display the aspect map layer on the graphics monitor before run‐
81 ning d.rast.arrow. The second method involves setting the map parame‐
82 ter to the name of the desired aspect map. This allows the arrows to
83 be drawn over any other maps already displayed on the graphics monitor.
84 d.rast.arrow will draw an arrow over each displayed cell to indicate in
86 which direction the cell slopes. If the aspect layer has a category
87 value denoting locations of "unknown" aspect, d.rast.arrow draws a
88 question mark over the displayed cells of that category. Cells con‐
89 taining null data will be marked with an "X". You can disable drawing
90 of null data and unknown aspect values by setting its color to "none".
91 When specifying the magnitude_map option, arrow lengths denoting magni‐
93 tude will be extracted from the cell values of the specified map. In
94 this case the tail of the arrow will be centered on the source cell.
95 You may adjust the overall scale using the scale option. d.rast.arrow
96 will ignore NULL and negative magnitudes, and will warn you if the de‐
97 bug level is set at 5 or higher. Be aware. If your application uses
98 negative values for magnitude, you can use r.mapcalc to prepare the
99 magnitude map to suit your needs (absolute value, inverted direction
100 and so on).
101
103 By default, arrows are drawn at the size of a cell and cannot be seen
104 if the raster map is relatively close in scale. You can use the skip
105 option to draw arrows every n-th cell in both directions if you are
106 working with relatively high resolutions. It may be useful to disable
107 the grid in this case, which is accomplished by setting its color to
108 "none".
109 For GRASS and Compass type aspect maps, the cell values of the aspect
111 map will determine the corresponding direction in 360 degrees. ANSWERS
112 type aspect maps will be plotted in multiples of 15 degrees counter‐
113 clockwise from east, and AGNPS and Drainage type aspect maps will be
114 displayed in D8 representation, i.e. the eight multiples of 45 degrees.
115 Cell values are 1 to 8 clockwise from north for AGNPS and 1 to 8 coun‐
116 terclockwise from north east for Drainage. See r.watershed for more de‐
117 tails about the Drainage aspect.
118 GRASS aspect maps are measured using Cartesian conventions, i.e. in de‐
120 grees counterclockwise from east. e.g.:
121 90 North
122 180 West
123 270 South
124 0,360 East
125 They can be created from a raster elevation map with r.slope.aspect.
126 Compass type aspect maps are measured in degrees clockwise from north.
128 This module uses oceanographic conventions, i.e. arrows point downslope
130 or direction "to", as opposed to atmospheric conventions (direction
131 "from").
132
134 Convert U,V velocity component maps into magnitude,direction maps for
135 use with d.rast.arrow:
136 r.mapcalc "magnitude = sqrt(U_map^2 + V_map^2)"
137 r.mapcalc "direction = atan(U_map, V_map)"
138 d.rast.arrow map=direction type=grass magnitude_map=magnitude skip=3 grid=none
139 Sea wind speed (magnitude) and direction shown in the Tasmanian Sea
140
142 d.frame, d.rast, d.rast.edit, d.rast.num, g.region, r.slope.aspect,
143 r.watershed
144
146 Original author
147 Chris Rewerts
148 Agricultural Engineering,
149 Purdue University
150 Magnitude and 360 arrow code
151 Hamish Bowman
152 Department of Marine Science,
153 University of Otago, New Zealand
154 Align grids with raster cells and Drainage aspect type
155 Huidae Cho
156
158 Available at: d.rast.arrow source code (history)
159 Accessed: Mon Jun 20 16:45:47 2022
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164 © 2003-2022 GRASS Development Team, GRASS GIS 8.2.0 Reference Manual
166GRASS 8.2.0 d.rast.arrow(1)