r.los(1) - f14

1r.los(1)                      Grass User's Manual                     r.los(1)
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NAME

6       r.los  - Line-of-sight raster analysis program.
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KEYWORDS

9       raster
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SYNOPSIS

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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DESCRIPTION

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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NOTES

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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EXAMPLE

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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TODO

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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AUTHOR

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)