angdist

Returns the angular distance in radians between two vectors. The input vectors do not have to be normalised. For almost colinear or anti-colinear vectors, renders numerically more accurate results than the $\cos^{-1}$ of the scalar product.

Location in HEALPix directory tree: src/f90/mod/pix_tools.F90 

FORMAT

call angdist( v1, v2, dist )

ARGUMENTS

name & dimensionality	kind	in/out	description
v1(3)	DP	IN	cartesian vector.
v2(3)	DP	IN	cartesian vector.
dist	DP	OUT	angular distance in radians between the 2 vectors.

EXAMPLE:

use healpix_types
use pix_tools, only : angdist
real(DP) :: dist, one = 1.0_dp
call angdist((/1,2,3/)*one, (/1,2,4/)*one, dist)
print*, dist

Returns the angular distance between 2 vectors.

RELATED ROUTINES

This section lists the routines related to angdist

ang2vec

converts the position angles of a point on the sphere into its 3D position vector.

vec2ang

converts the 3D position vector of point into its position angles on the sphere.

vect_prod

computes the vector product between two 3D vectors