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 [$3\pi/4$,$\pi$]

Version 3.31, 2017-01-06