query_polygon

Routine to find the index of all pixels enclosed in a polygon. The polygon should be convex, or have only one concave vertex. The edges should not intersect each other. The output indices can be either in the RING or NESTED scheme

Location in HEALPix directory tree: src/f90/mod/pix_tools.F90 

FORMAT

call query_polygon( nside, vlist, nv, listpix, nlist[, nest, inclusive] )

ARGUMENTS

name & dimensionality	kind	in/out	description
nside	I4B	IN	the $N_{\mathrm{side}}$ parameter of the map.
vlist(1:3,0:*)	DP	IN	cartesian vector pointing at polygon respective vertices.
nv	I4B	IN	number of vertices, should be equal to 3 or larger.
listpix(0:*)	I4B/ I8B	OUT	the index for all pixels enclosed in the triangle. Make sure that the size of the array is big enough to contain all pixels.
nlist	I4B/ I8B	OUT	The number of pixels listed in listpix.
nest (OPTIONAL)	I4B	IN	The pixel indices are in the NESTED numbering scheme if nest=1, and in RING scheme otherwise.
inclusive (OPTIONAL)	I4B	IN	If set to 1, all the pixels overlapping (even partially) with the polygon are listed, otherwise only those whose center lies within the polygon are listed.

EXAMPLE:

use healpix_modules
real(dp), dimension(1:3,0:9) :: vertices
vertices(:,0) = (/0.,0.,1./) ! +z
vertices(:,1) = (/1.,0.,0./) ! +x
vertices(:,2) = (/1.,1.,-1./) ! x+y-z
vertices(:,3) = (/0.,1.,0./) ! +y

call query_polygon(256,vertices,4,listpix,nlist,nest=0)

Returns the RING pixel index of all pixels in the polygon with vertices of cartesian coordinates (0,0,1), (1,0,0), (1,1,-1) and (0,1,0) in a $N_{\mathrm{side}}=256$ map.

MODULES & ROUTINES

This section lists the modules and routines used by query_polygon.

isort

routine to sort integer number

query_triangle

render the list of pixels enclosed in a given triangle

surface_triangle

computes the surface of a spherical triangle defined by 3 vertices

vect_prod

routine to compute the vectorial product of two 3D vectors

RELATED ROUTINES

This section lists the routines related to query_polygon

pix2ang, ang2pix

convert between angle and pixel number.

pix2vec, vec2pix

convert between a cartesian vector and pixel number.

query_disc, query_polygon,

query_strip, query_triangle

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

surface_triangle

computes the surface in steradians of a spherical triangle defined by 3 vertices