Thursday, 22 December 2016

Polar plot in Gnuplot

I was recently playing with microphone array polar diversity responses and did a search for suitable Gnuplot solutions. There are a number that turned up but none of them really matched my requirement so here it is :

set polar
set angle degree
set size ratio 1
set tmargin 3
set bmargin 3
set title "Microphone Polar Diversity Response : Mic Spacing 0.1 (meters)"
set key out vert nobox

set style line 1 lc rgb 'gray80' lt -1
set grid polar ls 1

unset border
unset xtics
unset ytics

f_maxGain=0.                                    # Maximum gain - MUST BE FLOATING POINT
minGain=-80                                     # Minimum gain - MUST BE INTEGER
tickstep = 10                                   # Ticks every 10 dB
numticks = 8                                    # numticks = r / tickstep :: Don't use divide because numticks is used in for loop and doesn't work
f_numticks = 8.                                 # Floating point numticks


set rrange [minGain:0]
set rtics tickstep format '' scale 0

set label '0°' center at first 0, first -minGain*1.05
set label '90°' right at first -minGain*1.05, 0
set label '180°' center at first 0, first minGain*1.05
set label '270°' left at first minGain*1.05, 0

set for [i=.1:numticks] label at first minGain*0.001, first minGain*((i/f_numticks) + 0.007) sprintf("%d dB", minGain+(i*10))
unset raxis

plot "250.dat" u (-$1+90.):($2-f_maxGain) t "250 Hz" w lines lc rgb "magenta", \
      "500.dat" u (-$1+90.):($2-f_maxGain) t "500 Hz" w lines lc rgb "red", \
      "1000.dat" u (-$1+90.):($2-f_maxGain) t "1000 Hz" w lines lc rgb "blue", \
      "2000.dat" u (-$1+90.):($2-f_maxGain) t "2000 Hz" w lines lc rgb "cyan", \
      "4000.dat" u (-$1+90.):($2-f_maxGain) t "4000 Hz" w lines lc rgb "orange"

print "Hit <CR> to continue ..."
pause -1

The data was generated in a C program. The files look like this (i.e. two columns angle and gain) :

# Antenna Beam Pattern
# Angle Gain
-9.00e+01 -1.17e+00
-8.90e+01 -1.17e+00
-8.80e+01 -1.17e+00
.
.

Here is the plot for 100 mm mic spacing :


The gnuplot script allows the min and max gain values to be changed.

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