1r.los(1) Grass User's Manual r.los(1)
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6 r.los - Line-of-sight raster analysis program.
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9 raster
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12 r.los
13 r.los help
14 r.los input=name output=name coordinate=x,y [patt_map=name]
15 [obs_elev=float] [max_dist=float] [--overwrite] [--verbose]
16 [--quiet]
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18 Flags:
19 --overwrite
20 Allow output files to overwrite existing files
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22 --verbose
23 Verbose module output
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25 --quiet
26 Quiet module output
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28 Parameters:
29 input=name
30 Name of elevation raster map
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32 output=name
33 Name for output raster map
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35 coordinate=x,y
36 Coordinate identifying the viewing position
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38 patt_map=name
39 Binary (1/0) raster map to use as a mask
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41 obs_elev=float
42 Viewing position height above the ground
43 Default: 1.75
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45 max_dist=float
46 Maximum distance from the viewing point (meters)
47 Options: 0-999999
48 Default: 10000
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51 r.los generates a raster output map in which the cells that are visible
52 from a user-specified observer position are marked with the vertical
53 angle (in degrees) required to see those cells (viewshed). A value of
54 0 is directly below the specified viewing position, 90 is due horizon‐
55 tal, and 180 is directly above the observer. The angle to the cell
56 containing the viewing position is undefined and set to 180.
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58 To run r.los, the user must specify at least an input map name, output
59 map name, and the geographic coordinates of the user's viewing loca‐
60 tion; any remaining parameters whose values are unspecified will be set
61 to their default values (see below).
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63 The patt_map is the name of a binary (1/0) raster map layer in which
64 cells within the areas of interest are assigned the category value '1',
65 and all other cells are assigned the category value '0' or NULL. If
66 this parameter is omitted, the analysis will be performed for the whole
67 area within a certain distance of the viewing point inside the geo‐
68 graphic region boundaries.
69 Default: assign all cells that are within the max_dist and within the
70 user's current geographic region boundaries a value of 1.
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72 The obs_elev parameter defines the height of the observer (in meters)
73 above the viewing point's elevation.
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75 The max_dist parameter is the maximum distance (in meters) from the
76 viewing point inside of which the line of sight analysis will be per‐
77 formed. The cells outside this distance range are assigned a NULL
78 value.
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81 For accurate results, the program must be run with the resolution of
82 the geographic region set equal to the resolution of the data (see
83 g.region).
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85 The time to complete the calculation increases dramatically with the
86 region size. Try to keep the columns and rows under 1000.
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88 It is advisable to use a 'pattern layer' which identifies the areas of
89 interest in which the line of sight analysis is required. Such a mea‐
90 sure will reduce the time taken by the program to run.
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92 The curvature of the Earth is not taken into account for these calcula‐
93 tions. However, for interest's sake, a handy calculation for distance
94 to the true horizon is approximated by d = sqrt(13*h) where h is the
95 height of the observer in meters (above sea level) and d is the dis‐
96 tance to the horizon in km. This may be useful for setting the
97 max_dist value.
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100 Spearfish example - calculation of viewshed from 50m tower on top of a
101 mountain:
102 r.los elevation.dem out=los coord=598869,4916642 obs_elev=50
103 max_dist=10000
104 r.colors -e los color=bgyr
105 d.shadedmap relief=aspect drape=los bright=10
106 echo "symbol extra/target 25 598869 4916642 red" | d.graph -m
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110 Rewrite using ideas from r.cva and a method which scales better to
111 large regions.
112 A suggested method is detailed in: Izraelevitz, David (USACE).
113 ’A Fast Algorithm for Approximate Viewshed Computation'
114 Photogrammetric Engineering & Remote Sensing, July 2003
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117 g.region
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120 Kewan Q. Khawaja, Intelligent Engineering Systems Laboratory, M.I.T.
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122 Last changed: $Date: 2007-12-17 14:53:55 +0100 (Mon, 17 Dec 2007) $
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124 Full index
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126 © 2003-2008 GRASS Development Team
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130GRASS 6.3.0 r.los(1)