Mapping Hacks

356

|

Chapter 6, Mapping on Your Desktop

#74 Plot Wireless Network Viewsheds with GRASS

HACK

HACK

#74

Plot Wireless Network Viewsheds with

GRASS Hack #74

With a little GRASS scripting, you can build sophisticated models of radio-

frequency reception for wireless network planning—and find out where the

black holes are.

If your local terrain is hilly, planning wireless community networks can be a

big hassle, as 802.11 depends on line-of-sight between nodes. “Planning” is

somewhat of a misnomer; networks grow organically according to move-

ments of people. When you move to a new town, the question “Can I get on

your free network?” is most often answered with “We don’t know!” Before

we start hanging out of the window waving an antenna about, we can start

answering this question with viewshed maps, which display the area visible

from a given point on an elevation model. Knowing where you can’t get

directly connected from is a good start.

In “Why You Can’t Watch Broadcast TV”

[Hack #18], we used a tool called

SPLAT! for mapping radio viewsheds. Although SPLAT! is easy to use, it

also has several shortcomings. In this hack, we’ll look at doing much more

sophisticated modeling with GRASS. Using GRASS, we can map wireless

viewsheds over any arbitrary base map, taking terrain effects and antenna

height, angle, and beam width into account.

Being geeks, when we moved to San Francisco, the first thing we wanted to

do ...