# angDist

Compute angular distance between pixel centers or points on the sphere

## Contents

- Syntax
- Input Arguments
- Return Arguments
- Description
- v0 or v1 specified as numeric arrays
- pix0 or pix1 specified as cell arrays
- Example
- See also
- Requires

## Syntax

     rad = angDist(v0,v1,'Param1',Value1,'Param2',Value2,...)

## Input Arguments

    v0, v1      (numerical or cell) array of points on sphere

    Param       Value
    'nSide'     HEALPix resolution parameter (integer power 2)
    'nest'      nested indexing (true | {false})

## Return Arguments

     rad     array of angular distances (radians)

## Description

angDist computes the angular distances between points on the sphere. Points may be specified as MEALPix pixel numbers, spherical coordinate location vectors, or cartesian coordinate vectors. Cartesian coordinate input vectors need not be normalized.

Either or both of v0, v1 may be a scalar; otherwise they must both be the same size. When one is a scalar than the distance is computed between that point and all the points specified in the complementary argument. When pix0 and pix1 are arrays then the distances are returned between the corresponding points in the two arrays.

If any location is specified as a pixel number than nSide must be specified. The indexing scheme for pixels center locations defaults to ring; to specify nested indexing set the 'nest' parameter to true.

## v0 or v1 specified as numeric arrays

If all points in v0 are pixel numbers then v0 may be specified as a numeric array (similarly v1, mutatis mundis). then nSide must be specified. Pixels numbers may be specified in ring indexing or nested indexing. For nested indexing the nest flag must be specified as true.

## pix0 or pix1 specified as cell arrays

Either or both pix0 or pix1 may be specified as a cell array, in which case each cell specifies a location on the sphere as either a pixel number, a two-component ([theta; phi]) spherical coordinate vector, or a three component ([x;y;z]) cartesian vector. nSide must be specified if any location is identified as a pixel center.

## Example

     % angular distance from pole to equator:
     v0 = {[0;0;1]}; % north pole
     v1 = {[1;0;0]}; % point on equator
     rad = angDist(v0, v1);

     % angular distance from pole to pixels 1, 17, 33 for nSide = 4:
     v0 = {[0;0;1]};
     rad = angDist([1, 17, 33], v0, 'nSide', 4)

     % angular distance from pixels 1 to 4, 2 to 5, and 3 to 6 for nSide = 8:
     rad = angDist([1, 2, 3], [4, 5, 6],'nSide',8)

    rad =

        0.2045    0.6224    0.8411

    rad =

        0.1443    0.2609    0.3013

## See also

queryDisc

## Requires

pix2vec, ang2vec

Copyright 2010-2011 Lee Samuel Finn. Terms of Use.