
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_{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 
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 
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:
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+yz
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_{side}=256 map.
MODULES & ROUTINESThis 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 ROUTINESThis 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
Eric Hivon
20100618

