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query_polygon
This IDL facility provides a means to find the index of all pixels belonging to
a sperical polygon defined by its vertices
Location in HEALPix directory tree:
src/idl/toolkit/query_polygon.pro
FORMAT IDL>
query_polygon , Nside, Vlist, Listpix, [Nlist, HELP=, NESTED=, INCLUSIVE=]
QUALIFIERS
-
Nside
- HEALPix resolution parameter used to index the pixel list (scalar integer)
-
Vlist
- 3D cartesian position vector of the polygon vertices. Array of
dimension (n,3) where n is the number of vertices
-
Listpix
- on output: list of ordered index for the pixels found
in the polygon. The RING numbering scheme is used unless the keyword NESTED is set.
(=-1 if the polygon is too small and no pixel is found)
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Nlist
- on output: number of pixels in Listpix (=0 if no pixel is found).
KEYWORDS
-
HELP=
- if set, the documentation header is printed out and the
routine exits
-
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 polygon are listed, otherwise only those whose
center lies within the polygon are listed
DESCRIPTION
query_polygon finds the pixels within the given polygon in a selective way WITHOUT
scanning all the sky pixels. The polygon should be convex,
or have only one concave vertex. The edges should not intersect each other.
The numbering scheme of the output list and the
inclusiveness of the polygon can be changed
RELATED ROUTINESThis section lists the routines related to query_polygon
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idl
- version 6.1 or more is necessary to run query_polygon .
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ang2pix, pix2ang
- conversion between angles and pixel index
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vec2pix, pix2vec
- conversion between vector and pixel index
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query_disc, query_polygon,
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query_strip, query_triangle
- render the list of pixels enclosed
respectively in a given disc, polygon, latitude strip and triangle
EXAMPLE:
On return listpix contains the index of the (131191) pixels contained in the
polygon with vertices of cartesian coordinates (0,0,1), (1,0,0), (1,1,-1) and (0,1,0).
The pixel indices correspond to the RING scheme with resolution 256.
Eric Hivon
2010-06-18
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