vsepg_c |

Table of contents## Procedurevsepg_c ( Angular separation of vectors, general dimension ) SpiceDouble vsepg_c ( ConstSpiceDouble * v1, ConstSpiceDouble * v2, SpiceInt ndim ) ## AbstractFind the separation angle in radians between two double precision vectors of arbitrary dimension. This angle is defined as zero if either vector is zero. ## Required_ReadingNone. ## KeywordsANGLE VECTOR ## Brief_I/OVARIABLE I/O DESCRIPTION -------- --- -------------------------------------------------- v1 I First vector. v2 I Second vector. ndim I The number of elements in `v1' and `v2'. The function returns the angle between `v1' and `v2' expressed in radians. ## Detailed_Inputv1, v2 are two double precision vectors of arbitrary dimension. Either `v1' or `v2', or both, may be the zero vector. An implicit assumption exists that `v1' and `v2' are specified in the same reference space. If this is not the case, the numerical result of this routine has no meaning. ndim is the dimension of both `v1' and `v2'. ## Detailed_OutputThe function returns the angle between `v1' and `v2' expressed in radians. ## ParametersNone. ## ExceptionsError free. ## FilesNone. ## ParticularsIn four or more dimensions this angle does not have a physically realizable interpretation. However, the angle is defined as the generalization of the following definition which is valid in three or two dimensions: In the plane, it is a simple matter to calculate the angle between two vectors once the two vectors have been made to be unit length. Then, since the two vectors form the two equal sides of an isosceles triangle, the length of the third side is given by the expression length = 2.0 * sin ( ## ExamplesThe numerical results shown for this example may differ across platforms. The results depend on the SPICE kernels used as input, the compiler and supporting libraries, and the machine specific arithmetic implementation. 1) Define two sets of n-dimensional vectors and compute the angular separation between each vector in first set and the corresponding vector in the second set. Example code begins here. /. Program vsepg_ex1 ./ #include <stdio.h> #include "SpiceUsr.h" int main( ) { /. Local parameters. ./ #define NDIM 4 #define SETSIZ 3 /. Local variables. ./ SpiceInt i; /. Define the two vector sets. ./ SpiceDouble v1 [SETSIZ][NDIM] = { {1.0, 0.0, 0.0, 0.0}, {1.0, 0.0, 0.0, 0.0}, {3.0, 0.0, 0.0, 0.0} }; SpiceDouble v2 [SETSIZ][NDIM] = { { 1.0, 0.0, 0.0, 0.0}, { 0.0, 1.0, 0.0, 0.0}, {-5.0, 0.0, 0.0, 0.0} }; /. Calculate the angular separation between each pair of vectors. ./ for ( i = 0; i < SETSIZ; i++ ) { printf( "First vector : %5.1f %5.1f %5.1f %5.1f\n", v1[i][0], v1[i][1], v1[i][2], v1[i][3] ); printf( "Second vector : %5.1f %5.1f %5.1f %5.1f\n", v2[i][0], v2[i][1], v2[i][2], v2[i][3] ); printf( "Angular separation (rad): %14.10f\n", ## Restrictions1) The user is required to insure that the input vectors will not cause floating point overflow upon calculation of the vector dot product since no error detection or correction code is implemented. In practice, this is not a significant restriction. ## Literature_ReferencesNone. ## Author_and_InstitutionC.A. Curzon (JPL) J. Diaz del Rio (ODC Space) K.R. Gehringer (JPL) H.A. Neilan (JPL) W.L. Taber (JPL) E.D. Wright (JPL) ## Version-CSPICE Version 1.0.1, 31-JUL-2020 (JDR) Edited the header to comply with NAIF standard. Added complete code example based on existing example. -CSPICE Version 1.0.0, 29-JUN-1999 (EDW) (WLT) (HAN) (KRG) (CAC) ## Index_Entriesangular separation of n-dimensional vectors |

Fri Dec 31 18:41:15 2021