query_strip

This IDL facility provides a means to find the index of all pixels belonging to a latitude strip defined by its bounds

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

FORMAT

IDL> query_strip , Nside, Theta1, Theta2, Listpix, [Nlist, NESTED=, INCLUSIVE=, HELP=]

QUALIFIERS

Nside

HEALPix resolution parameter used to index the pixel list (scalar integer)

Theta1

colatitude lower bound in radians measured from North Pole (between 0 and $\pi$).

Theta2

colatitude upper bound in radians measured from North Pole (between 0 and $\pi$). If theta1< theta2, the pixels lying in [theta1,theta2] are output, otherwise, the pixel lying in [0, theta2] and those lying in [theta1, $\pi$] are output.

Listpix

on output: list of ordered index for the pixels found in the strip. The RING numbering scheme is used unless the keyword NESTED is set. (=-1 if the strip is too small and no pixel is found)

Nlist

on output: number of pixels in Listpix (=0 if no pixel is found).

KEYWORDS

NESTED=

if set, the output list uses the NESTED numbering scheme instead of the default RING

INCLUSIVE=

if set, all the pixels overlapping (even partially) with the strip are listed, otherwise only those whose center lies within the strip are listed

/HELP

if set, the routine prints its documentation header and exits.

DESCRIPTION

query_strip finds the pixels within the given strip in a selective way WITHOUT scanning all the sky pixels. The numbering scheme of the output list and the inclusiveness of the strip can be changed

RELATED ROUTINES

This section lists the routines related to query_strip

idl

version 6.4 or more is necessary to run query_strip .

ang2pix, pix2ang

conversion between angles and pixel index

vec2pix, pix2vec

conversion between vector and pixel index

query_disc, query_polygon,

query_triangle

render the list of pixels enclosed respectively in a given disc, polygon and triangle

EXAMPLE:

query_strip , 256, 0.75*!PI, !PI/5, listpix, nlist, /nest

Returns the NESTED pixel index of all pixels with colatitude in [0,$\pi/5$] and those with colatitude in [$3\pi/4$,$\pi$]