Graphics Programs Reference

In-Depth Information

16 Polar Plots

When displaying information which varies as a function of angle, it is

often beneficial to use a polar diagram in which conventional (
x, y
) values

are interpreted as angle and radius. Compare the following two displays.

First the conventional (
x, y
) plot:

clf

t = linspace(-pi,pi,201);

g = sinc(2.8*sin(t));

plot(t*180/pi,g)

zeroaxes

(The command
zeroaxes
is part of the companion software to this

topic.) Then the polar diagram indicating the directional variation in

the quantity
g
:

clf

polar(t,g)

Plots such as these are sometimes displayed in decibel units:

gdb = 10*log10(abs(g));

plot(t*180/pi,gdb)

zeroaxes

But the polar diagram in this case gives rubbish because it is interpreting

the negative decibel values as negative radii: