Polarplot: logscale r axis possible?
Christian Winkel
after plotting a lot of normal xy diagrams I now have to plot a polar
plot with a logscale r axis.
Is that possible?
I googled for hours and tried many options, but can't find a way to plot
the data in log-scale.
chris
Christian Winkel
I've go a solution on the gnuplot mailinglist.
Maybe somebody is interested in this solution from Thomas Sefzick:
apply the log10() function to your data and shift the resulting r range
to positive values (starting from zero).
an example:
# rrange goes from 10^-4 = 0.0001 to 10^0 = 1.
# so log10(rrange) goes from -4 to 0 and must be
# shifted to 0 to 4
reset
set angles radians
set grid polar pi/6.
unset label
set label 1 "0.0001" at 0, -0.2
set label 2 "0.001" at 1, -0.2
set label 3 "0.01" at 2, -0.2
set label 4 "0.1" at 3, -0.2
set label 5 "1.0" at 4, -0.2
unset arrow
set arrow 1 from 0,0 to 4,0 nohead
set polar
set samples 1000, 1000
set size square
set rrange [0:4]
set xrange [-4:4]
set yrange [-4:4]
# some function producing values in the range
# 0.0001 to (nearly) 1.0
f(t)=0.99*(sin(t+0.5*pi)**2+10**(-4))
# plot the function (multiplied by 4. to have the same range)
plot f(t)*4.
# plot log10() of the function (shifted by 4.)
replot log10(f(t))+4.
pause -1
# and now without border
unset border
set format x ""
set format y ""
set xtics scale 0
set ytics scale 0
replot