Draw a blank map of the world in polyconic projection with GMT

polyconic.sh

#!/bin/sh
ps=polyconic_coast.ps
w=2.0944c
proj=Poly/${w}
lon0=-180
lon1=`expr ${lon0} + 30`
reg=${lon0}/${lon1}/-90/90
gmt psbasemap -R${reg} -J${proj} -K -Bg10/g10 > ${ps}
gmt pscoast -R${reg} -J${proj} -O -K -W -B >> ${ps}
while [ ${lon0} -lt 120 ]; do
  lon0=${lon1}
  lon1=`expr ${lon0} + 30`
  reg=${lon0}/${lon1}/-90/90
  gmt psbasemap -X${w} -R${reg} -J${proj} -O -K -B >> ${ps}
  gmt pscoast -R${reg} -J${proj} -O -K -W -B >> ${ps}
done
lon0=${lon1}
lon1=`expr ${lon0} + 30`
reg=${lon0}/${lon1}/-90/90
gmt psbasemap -X${w} -R${reg} -J${proj} -O -K -B >> ${ps}
gmt pscoast -R${reg} -J${proj} -O -W -B >> ${ps}
ps2pdf ${ps}
pdfcrop ${ps%s}df
rm ${ps} ${ps%s}df