Mapping Hacks

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Chapter 6, Mapping on Your Desktop

#74 Plot Wireless Network Viewsheds with GRASS

HACK

map; otherwise, we leave it out. (Note that r.mapcalc does loads more than

this; take a look at its manpage to get a sense of its scope.)

Generating the Line-of-Sight Layer

The following is the entirety of a GRASS script we concocted called r.slice.sh,

a shell script that wraps r.mapcalc to generate r.los pattern-map layers:

#!/bin/bash

for i

do

case $i in

arc=*)

arc=${i#arc=} ;;

azi*=*)

azimuth=${i#azi*=} ;;

map=*)

map=${i#map=} ;;

coord*=*)

coord=${i#coord*=}; x=${coord%,*}; y=${coord#*,} ;;

esac

done

if [ ! "$arc" -o ! "$azimuth" -o ! "$map" -o ! "$x" -o ! "$y" ];

then

echo "Usage: $(basename $0)"

echo " map=raster coordinates=x,y arc=value azimuth=value"

exit -1

fi

r.mapcalc <<EOF

$map = eval( \\

min = $azimuth - ($arc / 2), \\

max = $azimuth + ($arc / 2), \\

theta = atan( y( ) - $y, x( ) - $x ), \\

if( \\

((theta >= min) && (theta <= max)) || \\

((theta - 360 >= min) && (theta - 360 <= max)), \\

1, 0 ) \\

)

EOF

r.colors map=$map color=rules <<EOF

0 black

1 white

EOF

Once we have all the parameters we need, we feed them into r.mapcalc using

shell substitution in a here document. The extra clause in the r.mapcalc code

involving the

theta - 360 calculation handles the edge case where the

Plot Wireless Network Viewsheds ...