vec2ang

This IDL facility convert the 3D position vectors of points into their angles on the sphere.

Location in HEALPix directory tree: src/idl/toolkit/vec2ang.pro 

FORMAT

IDL> VEC2ANG , Vector, Theta, Phi[, ASTRO=]

QUALIFIERS

Vector

input, array,
three dimensional cartesian position vector (x,y,z) (not necessarily normalised). The north pole is (0,0,1). The coordinates are ordered as follows $x(0),\ldots,x(n-1),\ y(0),\ldots,y(n-1),\ z(0),\ldots,z(n-1)$

Theta

output, vector,
vector, colatitude in radians measured southward from north pole in [0,$\pi$] (mathematical coordinates).
If ASTRO is set, Theta is the latitude in degrees measured northward from the equator, in [-90, 90] (astronomical coordinates).

Phi

output, vector,
longitude in radians measured eastward, in [0, $2\pi$] (mathematical coordinates).
If ASTRO is set, Phi is the longitude in degree measured eastward, in [0,360] (astronomical coordinates).

KEYWORDS

ASTRO=

if set Theta and Phi are the latitude and longitude in degrees (astronomical coordinates) instead of the colatitude and longitude in radians (mathematical coordinates).

DESCRIPTION

vec2ang performs the geometrical transform from the 3D position vectors (x,y,z) of points into their angles $(\theta,\phi)$ on the sphere: $x = \sin\theta\cos\phi$, $y=\sin\theta\sin\phi$, $z=\cos\theta$

RELATED ROUTINES

This section lists the routines related to vec2ang

idl

version 6.4 or more is necessary to run vec2ang .

pix2xxx, ...

conversion between vector or angles and pixel index

ang2vec

conversion from angles to position vectors

EXAMPLE:

vec2ang, [[0.,0.],[0.,0.],[1.,-10.]], lat, lon, /astro
print,lat
print,lon

will return 90.0000, -90.0000 and 0.00000, 0.00000, the latitudes and longitudes in Degrees or the North and South poles. Note that in this example the input 3D location of South pole was not normalized.