CSPICE_PJELPL orthogonally projects an ellipse onto a plane.
For important details concerning this module's function, please refer to
the CSPICE routine pjelpl_c.
Given:
elin a SPICE ellipse structure. The structure has the fields:
center: [3array double]
semiMajor: [3array double]
semiMinor: [3array double]
plane a SPICE plane structure. The structure has the fields:
normal: [3array double]
constant: [scalar double]
are, respectively, a SPICE ellipse and a SPICE plane. The
geometric ellipse represented by 'elin' is to be orthogonally
projected onto the geometric plane represented by 'plane'.
the call:
cspice_pjelpl, elin, plane, elout
returns:
elout the SPICE ellipse structure that represents the geometric
ellipse resulting from orthogonally projecting the ellipse
represented by 'elin' onto the plane represented by 'plane'.
The structure has the fields:
center: [3array double]
semiMajor: [3array double]
semiMinor: [3array double]
Any numerical results shown for this example may differ between
platforms as the results depend on the SPICE kernels used as input
and the machine specific arithmetic implementation.
;;
;; Assign the values for plane/ellipse definition
;; vectors.
;;
center = [ 1.d, 1.d, 1.d ]
vect1 = [ 2.d, 0.d, 0.d ]
vect2 = [ 0.d, 1.d, 1.d ]
normal = [ 0.d, 0.d, 1.d ]
;;
;; Create a plane using a constant value of 0...
;;
cspice_nvc2pl, normal, 0.d, plane
;;
;; ...and an ellipse.
;;
cspice_cgv2el, center, vect1, vect2, elin
;;
;; Project the ellipse onto the plane.
;;
cspice_pjelpl, elin, plane, elout
;;
;; Output the ellipse in the plane.
;;
print, 'Center : ', elout.center
print, 'Semiminor: ', elout.semiminor
print, 'Semimajor: ', elout.semimajor
IDL outputs for the components of 'elout':
Center : 1.0000000 1.0000000 0.0000000
Semiminor: 0.0000000 1.0000000 0.0000000
Semimajor: 2.0000000 0.0000000 0.0000000
Projecting an ellipse orthogonally onto a plane can be thought of
finding the points on the plane that are `under' or `over' the
ellipse, with the `up' direction considered to be perpendicular
to the plane. More mathematically, the orthogonal projection is
the set of points Y in the plane such that for some point X in
the ellipse, the vector Y  X is perpendicular to the plane.
The orthogonal projection of an ellipse onto a plane yields
another ellipse.
ICY.REQ
ELLIPSES.REQ
PLANES.REQ
Icy Version 1.0.1, 13JUN2011, EDW (JPL)
Edits to comply with NAIF standard for Icy headers. Particulars section
now parallels Mice version.
Icy Version 1.0.0, 16JUN2003, EDW (JPL)
project ellipse onto plane
