d.rast.arrow(1)

1d.rast.arrow(1)               Grass User's Manual              d.rast.arrow(1)
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NAME

6       d.rast.arrow   -  Draws arrows representing cell aspect direction for a
7       raster map containing aspect data.
8

KEYWORDS

10       display
11

SYNOPSIS

13       d.rast.arrow
14       d.rast.arrow help
15       d.rast.arrow    [map=string]     [type=string]     [arrow_color=string]
16       [grid_color=string]       [x_color=string]       [unknown_color=string]
17       [skip=integer]   [magnitude_map=string]    [scale=float]    [--verbose]
18       [--quiet]
19
20   Parameters:
21       map=string
22           Name of raster aspect map to be displayed
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24       type=string
25           Type of existing raster aspect map
26           Options: grass,compass,agnps,answers
27           Default: grass
28
29       arrow_color=string
30           Color for drawing arrows
31           Options:                   red,orange,yellow,green,blue,indigo,vio‐
32           let,white,black,gray,brown,magenta,aqua,grey,cyan,purple
33           Default: green
34
35       grid_color=string
36           Color for drawing grid or "none"
37           Options:                   red,orange,yellow,green,blue,indigo,vio‐
38           let,white,black,gray,brown,magenta,aqua,grey,cyan,purple,none
39           Default: gray
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41       x_color=string
42           Color for drawing X's (Null values)
43           Options:                   red,orange,yellow,green,blue,indigo,vio‐
44           let,white,black,gray,brown,magenta,aqua,grey,cyan,purple
45           Default: black
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47       unknown_color=string
48           Color for showing unknown information
49           Options:                   red,orange,yellow,green,blue,indigo,vio‐
50           let,white,black,gray,brown,magenta,aqua,grey,cyan,purple
51           Default: red
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53       skip=integer
54           Draw arrow every Nth grid cell
55           Default: 1
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57       magnitude_map=string
58           Raster map containing values used for arrow length
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60       scale=float
61           Scale factor for arrows (magnitude map)
62           Default: 1.0
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DESCRIPTION

65       d.rast.arrow  is  designed to help users better visualize surface water
66       flow direction, as indicated in an aspect raster map layer.  There  are
67       two  ways to specify the aspect layer the program is to use.  The first
68       is to display the aspect map layer on the graphics monitor before  run‐
69       ning  d.rast.arrow.  The second method involves setting the map parame‐
70       ter to the name of the desired aspect map.  This allows the  arrows  to
71       be drawn over any other maps already displayed on the graphics monitor.
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73       d.rast.arrow will draw an arrow over each displayed cell to indicate in
74       which direction the cell slopes. If the aspect  layer  has  a  category
75       value  denoting  locations  of  "unknown"  aspect, d.rast.arrow draws a
76       question mark over the displayed cells of that  category.   Cells  con‐
77       taining null data will be marked with an "X".
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79       If  you specify the magnitude_map option, arrow lengths denoting magni‐
80       tude will be extracted from the cell values of the  specified  map.  In
81       this  case  the  tail of the arrow will be centered on the source cell.
82       You may adjust the overall scale using the scale option.   d.rast.arrow
83       will  ignore  NULL  and  negative  magnitudes, and will warn you if the
84       debug level is set at 5 or higher. Be aware. If your  application  uses
85       negative  values  for  magnitude,  you can use r.mapcalc to prepare the
86       magnitude map to suit your needs (absolute  value,  inverted  direction
87       and so on).
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NOTES

90       By  default,  arrows are drawn at the size of a cell and cannot be seen
91       if the raster map is relatively close in scale. You can  use  the  skip
92       option  to  draw  arrows  every n-th cell in both directions if you are
93       working with relatively high resolutions. It may be useful  to  disable
94       the  grid  in  this case, which is accomplished by setting its color to
95       "none".
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97       For GRASS and Compass type aspect maps, the cell values of  the  aspect
98       map  will determine the corresponding direction in 360 degrees. ANSWERS
99       type aspect maps will be plotted in multiples of 15 degrees, and  AGNPS
100       type aspect maps will be displayed in D8 representation, i.e. the eight
101       multiples of 45 degrees.
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103       GRASS aspect maps are measured using  Cartesian  conventions,  i.e.  in
104       degrees counterclockwise from east. e.g.:
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106              90  North
107              180 West
108              270 South
109              0,360 East
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111       They can be created from a raster elevation map with r.slope.aspect.
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113       Compass type aspect maps are measured in degrees clockwise from north.
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115       This module uses oceanographic conventions, i.e. arrows point downslope
116       or direction "to", as opposed  to  atmospheric  conventions  (direction
117       "from").
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EXAMPLE

120       Convert  U,V  velocity component maps into magnitide,direction maps for
121       use with d.rast.arrow:
122         r.mapcalc 'magnitude = sqrt(U_map^2 + V_map^2)'
123         r.mapcalc 'direction = atan(U_map, V_map)'
124         d.rast.arrow map=direction type=grass magnitude_map=magnitude  skip=3
125       grid=none
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AUTHORS

137       Original author
138       Chris Rewerts
139       Agricultural Engineering,
140       Purdue University
141       Magnitude and 360 arrow code
142       Hamish Bowman
143       Department of Marine Science,
144       University of Otago, New Zealand
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146       Last changed: $Date: 2005-10-18 06:58:58 +0200 (Tue, 18 Oct 2005) $
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148       Full index
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150       © 2003-2008 GRASS Development Team
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154GRASS 6.3.0                                                    d.rast.arrow(1)