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//
// GENERATED FILE
//
use super::*;
use crate::SpiceContext;
use f2rust_std::*;
/// Angular separation of vectors, 3 dimensions
///
/// Find the separation angle in radians between two double
/// precision, 3-dimensional vectors. This angle is defined as zero
/// if either vector is zero.
///
/// # Brief I/O
///
/// ```text
/// VARIABLE I/O DESCRIPTION
/// -------- --- --------------------------------------------------
/// V1 I First vector.
/// V2 I Second vector.
///
/// The function returns the angle between V1 and V2 expressed in
/// radians.
/// ```
///
/// # Detailed Input
///
/// ```text
/// V1,
/// V2 are two double precision 3-dimensional vectors. 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 frame. If this is not
/// the case, the numerical result of this routine has no
/// meaning.
/// ```
///
/// # Detailed Output
///
/// ```text
/// The function returns the angle between V1 and V2 expressed in
/// radians.
///
/// VSEP is strictly non-negative. If either V1 or V2 is the zero
/// vector, then VSEP is defined to be 0 radians.
/// ```
///
/// # Exceptions
///
/// ```text
/// Error free.
/// ```
///
/// # Particulars
///
/// ```text
/// 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 ( VSEP/2.0 )
///
/// The length is given by the magnitude of the difference of the
/// two unit vectors
///
/// LENGTH = NORM ( U1 - U2 )
///
/// Once the length is found, the value of VSEP may be calculated
/// by inverting the first expression given above as
///
/// VSEP = 2.0 * ARCSIN ( LENGTH/2.0 )
///
/// This expression becomes increasingly unstable when VSEP gets
/// larger than PI/2 radians or 90 degrees. In this situation (which
/// is easily detected by determining the sign of the dot product of
/// V1 and V2) the supplementary angle is calculated first and
/// then VSEP is given by
///
/// VSEP = PI - SUPPLEMENTARY_ANGLE
/// ```
///
/// # Examples
///
/// ```text
/// The 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 3-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 VSEP_EX1
/// IMPLICIT NONE
///
/// C
/// C SPICELIB functions.
/// C
/// DOUBLE PRECISION VSEP
///
/// C
/// C Local parameters.
/// C
/// INTEGER SETSIZ
/// PARAMETER ( SETSIZ = 3 )
///
/// C
/// C Local variables.
/// C
/// DOUBLE PRECISION V1 ( 3, SETSIZ )
/// DOUBLE PRECISION V2 ( 3, SETSIZ )
///
/// INTEGER I
/// INTEGER J
///
/// C
/// C Define the two vector sets.
/// C
/// DATA V1 / 1.D0, 0.D0, 0.D0,
/// . 1.D0, 0.D0, 0.D0,
/// . 3.D0, 0.D0, 0.D0 /
///
/// DATA V2 / 1.D0, 0.D0, 0.D0,
/// . 0.D0, 1.D0, 0.D0,
/// . -5.D0, 0.D0, 0.D0 /
///
/// C
/// C Calculate the angular separation between each pair
/// C of vectors.
/// C
/// DO I=1, SETSIZ
///
/// WRITE(*,'(A,3F6.1)') 'First vector : ',
/// . ( V1(J,I), J=1,3 )
/// WRITE(*,'(A,3F6.1)') 'Second vector : ',
/// . ( V2(J,I), J=1,3 )
/// WRITE(*,'(A,F15.10)') 'Angular separation (rad): ',
/// . VSEP ( V1(1,I), V2(1,I) )
/// WRITE(*,*)
///
/// END DO
///
/// END
///
///
/// When this program was executed on a Mac/Intel/gfortran/64-bit
/// platform, the output was:
///
///
/// First vector : 1.0 0.0 0.0
/// Second vector : 1.0 0.0 0.0
/// Angular separation (rad): 0.0000000000
///
/// First vector : 1.0 0.0 0.0
/// Second vector : 0.0 1.0 0.0
/// Angular separation (rad): 1.5707963268
///
/// First vector : 3.0 0.0 0.0
/// Second vector : -5.0 0.0 0.0
/// Angular separation (rad): 3.1415926536
/// ```
///
/// # Restrictions
///
/// ```text
/// 1) 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.
/// ```
///
/// # Author and Institution
///
/// ```text
/// J. Diaz del Rio (ODC Space)
/// K.R. Gehringer (JPL)
/// W.M. Owen (JPL)
/// W.L. Taber (JPL)
/// E.D. Wright (JPL)
/// ```
///
/// # Version
///
/// ```text
/// - SPICELIB Version 1.2.0, 05-JUL-2021 (JDR)
///
/// Added IMPLICIT NONE statement.
///
/// Edited the header to comply with NAIF standard. Removed
/// unnecessary $Revisions section.
///
/// Added complete code example based on existing example.
///
/// - SPICELIB Version 1.1.1, 17-APR-2006 (EDW)
///
/// Typo correction to the value of PI/2 in the $Examples
/// section, 1.571 instead of 1.71.
///
/// - SPICELIB Version 1.1.0, 29-FEB-1996 (KRG)
///
/// The declaration for the SPICELIB function PI is now
/// preceded by an EXTERNAL statement declaring PI to be an
/// external function. This removes a conflict with any
/// compilers that have a PI intrinsic function.
///
/// - SPICELIB Version 1.0.1, 10-MAR-1992 (WLT)
///
/// Comment section for permuted index source lines was added
/// following the header.
///
/// - SPICELIB Version 1.0.0, 31-JAN-1990 (WMO) (WLT)
/// ```
pub fn vsep(ctx: &mut SpiceContext, v1: &[f64; 3], v2: &[f64; 3]) -> f64 {
let ret = VSEP(v1, v2, ctx.raw_context());
ret
}
//$Procedure VSEP ( Angular separation of vectors, 3 dimensions )
pub fn VSEP(V1: &[f64], V2: &[f64], ctx: &mut Context) -> f64 {
let V1 = DummyArray::new(V1, 1..=3);
let V2 = DummyArray::new(V2, 1..=3);
let mut VSEP: f64 = 0.0;
let mut DMAG1: f64 = 0.0;
let mut DMAG2: f64 = 0.0;
let mut VTEMP = StackArray::<f64, 3>::new(1..=3);
let mut U1 = StackArray::<f64, 3>::new(1..=3);
let mut U2 = StackArray::<f64, 3>::new(1..=3);
//
// SPICELIB functions
//
//
// Local Variables
//
// The following declarations represent, respectively:
// Magnitudes of V1, V2
// Either of the difference vectors: V1-V2 or V1-(-V2)
// Unit vectors parallel to V1 and V2
//
//
// Calculate the magnitudes of V1 and V2; if either is 0, VSEP = 0
//
UNORM(V1.as_slice(), U1.as_slice_mut(), &mut DMAG1);
if (DMAG1 == 0.0) {
VSEP = 0.0;
return VSEP;
}
UNORM(V2.as_slice(), U2.as_slice_mut(), &mut DMAG2);
if (DMAG2 == 0.0) {
VSEP = 0.0;
return VSEP;
}
if (VDOT(U1.as_slice(), U2.as_slice()) > 0 as f64) {
VTEMP[1] = (U1[1] - U2[1]);
VTEMP[2] = (U1[2] - U2[2]);
VTEMP[3] = (U1[3] - U2[3]);
VSEP = (2.0 * f64::asin((0.5 * VNORM(VTEMP.as_slice()))));
} else if (VDOT(U1.as_slice(), U2.as_slice()) < 0 as f64) {
VTEMP[1] = (U1[1] + U2[1]);
VTEMP[2] = (U1[2] + U2[2]);
VTEMP[3] = (U1[3] + U2[3]);
VSEP = (PI(ctx) - (2.0 * f64::asin((0.5 * VNORM(VTEMP.as_slice())))));
} else {
VSEP = (PI(ctx) / 2.0);
}
VSEP
}