set pm3d depth lighting primary 0.75
set object rect from sc 0,0 to sc 1,1 behind fc "#003344"
set palette rgb 8,7,27
set samples 256
set isosamples 32
unset border
unset tics
unset colorbox
unset key
set xyplane 0
set view 65,30, 0.6,3
set term pngcairo size 360,360
set out "shell003.png"
set parametric
set urange[-18*pi:0]
set vrange[-7*pi/4:pi/4]

cot(x)=1/tan(x)
x(u,v)=(A*sin(b)*cos(u)+R*cos(v)*cos(u)-R*sin(m)*sin(v)*sin(u))*exp(u*cot(a))
y(u,v)=(-A*sin(b)*sin(u)-R*cos(v)*sin(u)-R*sin(m)*sin(v)*cos(u))*exp(u*cot(a))
z(u,v)=(-A*cos(b) + R*sin(v)*cos(m))*exp(u*cot(a))
D=1;a=pi/180*88.1;b=pi/45;m=pi/180;A=22.2;R=2.3
set zrange [:]
splot x(u,v), y(u,v), z(u,v) w pm3d

!display shell003.png