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.PS
# Orbits.m4
threeD_init
NeedDpicTools
crad = 1.0
g = 0.65
# `orbitpos(long,lat,rad,ang)'
define(`orbitpos',
`rot3Dx((`$2')*dtor_,rot3Dz((`$1')*dtor_,rot3Dy(-(`$4')*dtor_,`$3',0,0)))')
define(`PO',`B.C+(Project(orbitpos(orbitlong,orbitlat,orbitrad,`$1')))')
define vis { X: PO($1)
if (distance(X,B.C)>crad) || \
(dot3D(View3D,orbitpos(orbitlong,orbitlat,orbitrad,$1))>0) \
then {$2 = 1} else {$2 = -1} }
# `orbit(long,lat,rad)'
define(`orbit',
`[da = 3
orbitlong = `$1'
orbitlat = `$2'
orbitrad = `$3'
define(`decorated',`ifelse(`$4',,,`outlined `$4'')')
arrow from PO(0) to PO(da*3) decorated
n=0
P[n]: PO(0)
vis(0,v)
for d=da to 360 by da do {
vis(d,x)
if x*v < 0 then {
findroot(vis,d-da,d,1e-6,x)
n+=1; P[n]: PO(x)
if v < 0 then { fitcurve(P,n,dashed decorated) } \
else { fitcurve(P,n,decorated) }
P[0]: P[n]
n = 0; v = -v }
n +=1; P[n]: PO(d)
}
if v < 0 then { fitcurve(P,n,dashed decorated) } \
else { fitcurve(P,n,decorated) }
] with .c at B.C')
# ball(rad,highlight rad,highlight degrees)
define(`ball',`[
lt = linethick bp__
C: circle invis rad `$1' at (0,0)
D: C+(Rect_(`$2',`$3'))
rm = `$1'+distance(C,D)
a = 1 # fade rate parameter
for r=lt to rm by lt do {
u = 1-(r/rm*(a*r/rm+(1-a)))
if r < (1-g)*`$1' then { circle outlined rgbstring(u,u,u) rad r at D } \
else { arc cw outlined rgbstring(u,u,u) from Cintersect(D,r,C,`$1') \
to Cintersect(D,r,C,`$1',R) with .c at D
}
}
circle rad C.rad at C
]')
linethick = 0.8
B: ball(crad,crad*g,110)
azimuth = 0
elevation = 0
setview(azimuth,elevation)
orbit(10, 30,crad*1.3,"red")
orbit(10,-30,crad*1.3,"blue")
orbit(10,-90,crad*1.3,"cyan")
.PE
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