Table of contents
CSPICE_VCRSS computes the cross product of two 3-dimensional vectors.
Given:
v1,
v2 two 3-dimensional vectors.
help, v1
DOUBLE = Array[3]
help, v2
DOUBLE = Array[3]
Typically, these might represent the (possibly unit) vector to
a planet, Sun, or a star which defines the orientation of axes
of some reference frame.
the call:
cspice_vcrss, v1, v2, vout
returns:
vout the cross product of `v1' and `v2'.
help, vout
DOUBLE = Array[3]
None.
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.
1) Define two sets of vectors and compute the cross product of
each vector in first set and the corresponding vector in
the second set.
Example code begins here.
PRO vcrss_ex1
;;
;; Local parameters.
;;
SETSIZ = 2L
;;
;; Define the two vector sets.
;;
seta = [ [ 0.D0, 1.D0, 0.D0 ], [ 5.D0, 5.D0, 5.D0 ] ]
setb = [ [ 1.D0, 0.D0, 0.D0 ], [ -1.D0, -1.D0, -1.D0 ] ]
;;
;; Calculate the cross product of each pair of vectors
;;
for i=0L, SETSIZ-1L do begin
cspice_vcrss, seta[*,i], setb[*,i], vout
print, format='(A,3F5.1)', 'Vector A : ', seta[*,i]
print, format='(A,3F5.1)', 'Vector B : ', setb[*,i]
print, format='(A,3F5.1)', 'Cross product: ', vout
print, ' '
endfor
END
When this program was executed on a Mac/Intel/IDL8.x/64-bit
platform, the output was:
Vector A : 0.0 1.0 0.0
Vector B : 1.0 0.0 0.0
Cross product: 0.0 0.0 -1.0
Vector A : 5.0 5.0 5.0
Vector B : -1.0 -1.0 -1.0
Cross product: 0.0 0.0 0.0
cspice_vcrss calculates the three dimensional cross product of two
vectors according to the definition.
If `v1' and `v2' are large in magnitude (taken together, their
magnitude surpasses the limit allowed by the computer) then it
may be possible to generate a floating point overflow from an
intermediate computation even though the actual cross product may
be well within the range of double precision numbers. cspice_vcrss does
NOT check the magnitude of `v1' or `v2' to insure that overflow will
not occur.
Native IDL code to calculate the same vector result:
vout = crossp(v1,v2)
The native IDL function accepts arbitrary sized N vectors, but
ignores all but the first three components of the vectors. Both
vectors must consist of at least three elements.
1) If any of the input arguments, `v1' or `v2', is undefined, an
error is signaled by the IDL error handling system.
2) If any of the input arguments, `v1' or `v2', is not of the
expected type, or it does not have the expected dimensions and
size, an error is signaled by the Icy interface.
3) If the output argument `vout' is not a named variable, an
error is signaled by the Icy interface.
None.
1) No checking of `v1' or `v2' is done to prevent floating point
overflow. The user is required to determine that the
magnitude of each component of the vectors is within an
appropriate range so as not to cause floating point overflow.
In almost every case there will be no problem and no checking
actually needs to be done.
ICY.REQ
None.
J. Diaz del Rio (ODC Space)
E.D. Wright (JPL)
-Icy Version 1.0.2, 10-AUG-2021 (JDR)
Edited the header to comply with NAIF standard. Added complete
code example.
Added -Parameters, -Exceptions, -Files, -Restrictions,
-Literature_References and -Author_and_Institution sections, and
completed -Particulars section.
Removed reference to the routine's corresponding CSPICE header from
-Abstract section.
Added arguments' type and size information in the -I/O section.
-Icy Version 1.0.1, 09-DEC-2005 (EDW)
Added -Examples section.
-Icy Version 1.0.0, 16-JUN-2003 (EDW)
vector cross product
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