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]
18
19   Parameters:
20       map=string
21           Name of raster aspect map to be displayed
22
23       type=string
24           Type  of   existing   raster   aspect   map   Options:   grass,com‐
25           pass,agnps,answers Default: grass
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27       arrow_color=string
28           Color     for     drawing     arrows    Options:    red,orange,yel‐
29           low,green,blue,indigo,vio‐
30           let,white,black,gray,brown,magenta,aqua,grey,cyan,purple   Default:
31           green
32
33       grid_color=string
34           Color  for  drawing  grid,  or  "none"   Options:   red,orange,yel‐
35           low,green,blue,indigo,vio‐
36           let,white,black,gray,brown,magenta,aqua,grey,cyan,purple,none
37           Default: gray
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39       x_color=string
40           Color  for  drawing  X's  (Null  values)  Options:  red,orange,yel‐
41           low,green,blue,indigo,vio‐
42           let,white,black,gray,brown,magenta,aqua,grey,cyan,purple   Default:
43           black
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45       unknown_color=string
46           Color for  showing  unknown  information  Options:  red,orange,yel‐
47           low,green,blue,indigo,vio‐
48           let,white,black,gray,brown,magenta,aqua,grey,cyan,purple   Default:
49           red
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51       skip=integer
52           Draw arrow every Nth grid cell Default: 1
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54       magnitude_map=string
55           Raster map containing values used for arrow length
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57       scale=float
58           Scale factor for arrows (magnitude map) Default: 1.0
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DESCRIPTION

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

86       By  default,  arrows are drawn at the size of a cell and cannot be seen
87       if the raster map is relatively close in scale. You can  use  the  skip
88       option  to  draw  arrows  every n-th cell in both directions if you are
89       working with relatively high resolutions. It may be useful  to  disable
90       the  grid  in  this case, which is accomplished by setting its color to
91       "none".
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93       For GRASS and Compass type aspect maps, the cell values of  the  aspect
94       map  will determine the corresponding direction in 360 degrees. ANSWERS
95       type aspect maps will be plotted in multiples of 15 degrees, and  AGNPS
96       type aspect maps will be displayed in D8 representation, i.e. the eight
97       multiples of 45 degrees.
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99       GRASS aspect maps are measured using  Cartesian  conventions,  i.e.  in
100       degrees counterclockwise from east. e.g.:
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102              90  North
103              180 West
104              270 South
105              0,360 East
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107       They can be created from a raster elevation map with r.slope.aspect.
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109       Compass type aspect maps are measured in degrees clockwise from north.
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111       This module uses oceanographic conventions, i.e. arrows point downslope
112       or direction "to", as opposed  to  atmospheric  conventions  (direction
113       "from").
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EXAMPLE

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

133       Original author
134       Chris Rewerts
135       Agricultural Engineering,
136       Purdue University
137       Magnitude and 360 arrow code
138       Hamish Bowman
139       Department of Marine Science,
140       University of Otago, New Zealand
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142       Last changed: $Date: 2005/10/18 04:58:58 $
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144       Full index
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148GRASS 6.2.2                                                    d.rast.arrow(1)