Mapping Hacks

Plot Wireless Network Viewsheds with GRASS #74

Chapter 6, Mapping on Your Desktop

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HACK

by max_dist. Really, those values should be null (i.e., no data) instead of

zero, so that they don’t interfere with the display of underlying layers when

we put everything together, so let’s use the r.null tool to reset them:

GRASS:~/hacks/viewshed > r.null los setnull=0

Writing new data for [los]... 100%

GRASS:~/hacks/viewshed > d.redraw

100%

Superimposing Line-of-Sight and Base Map Layers

Now we can put everything together on one map:

GRASS:~/hacks/viewshed > d.erase

GRASS:~/hacks/viewshed > d.rast sf_topo

100%

GRASS:~/hacks/viewshed > d.rast -o los

100%

GRASS:~/hacks/viewshed > d.vect nodes display=shape,attr attrcol=str_1

icon=basic/box color=orange lcolor=orange bgcolor=white xref=left

yref=bottom

The -o option to d.rast tells it to overlay the los layer on top of the sf_topo

layer, rather than overwriting it, leaving the underlying layer present wher-

ever there are null values in the top layer. Note that we changed the site col-

ors to orange from blue, just to make them a little easier to see over the line-

of-sight plot. Figure 6-44 shows the result.

Not bad, eh? In Potrero Hill and Bernal Heights, we should think about buy-

ing wireless equipment, but maybe our friends on the eastern side of both

hills should wait until someone closer or more advantageously located gets

connected before obtaining their ...