vpack_c |
Table of contents
Procedurevpack_c ( Pack three scalar components into a vector ) void vpack_c ( SpiceDouble x, SpiceDouble y, SpiceDouble z, SpiceDouble v[3] ) AbstractPack three scalar components into a vector. Required_ReadingNone. KeywordsVECTOR Brief_I/OVARIABLE I/O DESCRIPTION -------- --- -------------------------------------------------- x, y, z I Scalar components of a vector. v O Equivalent vector. Detailed_Inputx, y, z are the scalar components of a 3-dimensional vector. Detailed_Outputv is the equivalent vector, such that v[0] = x v[1] = y v[2] = z ParametersNone. ExceptionsError free. FilesNone. ParticularsBasically, this is just shorthand notation for the common sequence v[0] = x; v[1] = y; v[2] = z; The routine is useful largely for two reasons. First, it reduces the chance that the programmer will make a "cut and paste" mistake, like v[0] = x; v[0] = y; v[0] = z; Second, it makes conversions between equivalent units simpler, and clearer. For instance, the sequence v[0] = x * rpd_c(); v[1] = y * rpd_c(); v[2] = z * rpd_c(); can be replaced by the (nearly) equivalent sequence vpack_c ( x, y, z, v ); vscl_c ( rpd_c(), v, v ); ExamplesThe numerical results shown for this example may differ across platforms. The results depend on the SPICE kernels used as input (if any), the compiler and supporting libraries, and the machine specific arithmetic implementation. 1) Compute an upward normal of an equilateral triangle lying in the x-y plane and centered at the origin. Example code begins here. /. Program vpack_ex1 ./ #include <math.h> #include <stdio.h> #include "SpiceUsr.h" int main( ) { /. Local variables ./ SpiceDouble normal [3]; SpiceDouble s; SpiceDouble v1 [3]; SpiceDouble v2 [3]; SpiceDouble v3 [3]; s = sqrt(3.0)/2; /. Define the three corners of the triangle. ./ vpack_c ( s, -0.5, 0.0, v1 ); vpack_c ( 0.0, 1.0, 0.0, v2 ); vpack_c ( -s, -0.5, 0.0, v3 ); /. Compute an upward normal of the triangle. ./ pltnrm_c ( v1, v2, v3, normal ); printf( "NORMAL = %16.13f %16.13f %16.13f\n", normal[0], normal[1], normal[2] ); return ( 0 ); } When this program was executed on a Mac/Intel/cc/64-bit platform, the output was: NORMAL = 0.0000000000000 0.0000000000000 2.5980762113533 RestrictionsNone. Literature_ReferencesNone. Author_and_InstitutionN.J. Bachman (JPL) J. Diaz del Rio (ODC Space) I.M. Underwood (JPL) Version-CSPICE Version 1.0.1, 16-JUL-2020 (JDR) Edited the header to comply with NAIF standard. Added complete code example. -CSPICE Version 1.0.0, 24-MAY-1999 (IMU) (NJB) Index_Entriespack three scalar components into a vector |
Fri Dec 31 18:41:15 2021