Table of contents
CSPICE_VUPACK unpacks three scalar components from a vector.
Given:
v a double precision 3-dimensional vector.
help, v
DOUBLE = Array[3]
the call:
cspice_vupack, v, x, y, z
returns:
x,
y,
z the double precision scalar components of the vector `v'.
help, x
DOUBLE = Scalar
help, y
DOUBLE = Scalar
help, z
DOUBLE = Scalar
The following equalities hold:
v[0] = x
v[1] = y
v[2] = z
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) Suppose that you have an instrument kernel that provides,
within a single keyword, the three frequencies used by the
instrument, and that you want to use these frequencies
independently within your code.
The following code example demonstrates how to use cspice_vupack
to get these frequencies into independent scalar variables.
Use the kernel shown below, an IK defining the three
frequencies used by an instrument with NAIF ID -999001.
KPL/IK
File name: vupack_ex1.ti
The keyword below define the three frequencies used by a
hypothetical instrument (NAIF ID -999001). They correspond
to three filters: red, green and blue. Frequencies are
given in micrometers.
\begindata
INS-999001_FREQ_RGB = ( 0.65, 0.55, 0.475 )
INS-999001_FREQ_UNITS = ( 'MICROMETERS' )
\begintext
End of IK
Example code begins here.
PRO vupack_ex1
;;
;; Local parameters.
;;
IKNAME = 'vupack_ex1.ti'
KEYWRD = 'INS-999001_FREQ_RGB'
;;
;; Load the instrument kernel.
;;
cspice_furnsh, IKNAME
;;
;; Get the frequency data from the kernel pool.
;;
cspice_gdpool, KEYWRD, 0L, 3L, ddata, found
if ( found ) then begin
cspice_vupack, ddata, red, green, blue
print, format='(A,F6.2)', 'Blue (nm): ', blue * 1000.D0
print, format='(A,F6.2)', 'Green (nm): ', green * 1000.D0
print, format='(A,F6.2)', 'Red (nm): ', red * 1000.D0
endif else begin
print, 'No data found in the kernel pool for ', KEYWRD
endelse
;;
;; It's always good form to unload kernels after use,
;; particularly in IDL due to data persistence.
;;
cspice_kclear
END
When this program was executed on a Mac/Intel/IDL8.x/64-bit
platform, the output was:
Blue (nm): 475.00
Green (nm): 550.00
Red (nm): 650.00
Basically, this is just shorthand notation for the common
sequence
x = v[0]
y = v[1]
z = v[2]
The routine is useful largely for two reasons. First, it
reduces the chance that the programmer will make a "cut and
paste" mistake, like
x = v[0]
y = v[0]
z = v[0]
Second, it makes conversions between equivalent units simpler,
and clearer. For instance, the sequence
x = v[0] * cspice_rpd()
y = v[1] * cspice_rpd()
z = v[2] * cspice_rpd()
can be replaced by the (nearly) equivalent sequence
cspice_vscl, cspice_rpd(), v, v
cspice_vupack, v, x, y, z
1) If the input argument `v' is undefined, an error is signaled
by the IDL error handling system.
2) If the input argument `v' 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 any of the output arguments, `x', `y' or `z', is not a
named variable, an error is signaled by the Icy interface.
None.
None.
ICY.REQ
None.
J. Diaz del Rio (ODC Space)
E.D. Wright (JPL)
-Icy Version 1.0.3, 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 1.0.2, 13-JUN-2011 (EDW)
Edits to comply with NAIF standard for Icy headers.
-Icy Version 1.0.1, 09-DEC-2005 (EDW)
Added -Examples section.
-Icy Version 1.0.0, 16-JUN-2003 (EDW)
unpack three scalar components from a vector
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