This IDL facility provides a means to find the index of all pixels within an
angular distance Radius from a defined center.
Location in HEALPix directory tree:
query_disc , Nside, Vector0, Radius, Listpix, [Nlist, DEG=, NESTED=, INCLUSIVE=]
- HEALPix resolution parameter used to index the pixel list (scalar integer)
- position vector of the disc center (3 elements vector)
NB : the norm of Vector0 does not have to be one, what is
consider is the intersection of the sphere with the line of
- radius of the disc (in radians, unless DEG is set), (scalar
- on output: list of ordered index for the pixels found
within a radius Radius of the position defined by vector0. The RING numbering
scheme is used unless the keyword NESTED is set.
(=-1 if the radius is too small and no pixel is found)
- on output: number of pixels in Listpix (=0 if no pixel is found).
- if set Radius is in degrees instead of radians
- if set, the output list uses the NESTED numbering scheme
instead of the default RING
- if set, all the pixels overlapping (even partially)
with the disc are listed, otherwise only those whose
center lies within the disc are listed
query_disc finds the pixels within the given disc in a selective way WITHOUT
scanning all the sky pixels. The numbering scheme of the output list and the
inclusiveness of the disc can be changed
This section lists the routines related to query_disc
- version 6.1 or more is necessary to run query_disc .
- conversion between angles and pixel index
- conversion between vector and pixel index
- render the list of pixels enclosed
respectively in a given disc, polygon, latitude strip and triangle
On return listpix contains the index of the (5982) pixels within 10 degrees from
the point on the sphere having the direction [.5,.5,0.].
The pixel indices correspond to the Nested scheme with resolution 256.