cdshealpix.ring.vertices_skycoord

cdshealpix.ring.vertices_skycoord(ipix, nside, step=1)

Get the sky coordinates of the vertices of some HEALPix cells at a given nside.

This method returns the 4 vertices of each cell in ipix. This method is wrapped around the vertices method from the cdshealpix Rust crate.

Parameters:

ipixnumpy.ndarray

The HEALPix cell indexes given as a np.uint64 numpy array.

nsideint

The nside of the HEALPix cells.

stepint, optional

The number of vertices returned per HEALPix side. By default it is set to 1 meaning that it will only return the vertices of the cell. 2 means that it will returns the vertices of the cell plus one more vertex per edge (the middle of it). More generally, the number of vertices returned is 4 * step.

Returns:

verticesastropy.coordinates.SkyCoord

The sky coordinates of the 4 vertices of the HEALPix cells. vertices is a SkyCoord object containing a \(N\) x \(4\) numpy array where N is the number of HEALPix cells given in ipix.

Raises:

ValueError

When the HEALPix cell indexes given have values out of \([0, 12\) x \(N_{side} ^ 2[\).

Examples

>>> from cdshealpix.ring import vertices_skycoord
>>> import numpy as np
>>> ipix = np.array([42, 6, 10])
>>> depth = 12
>>> vertices = vertices_skycoord(ipix, 1 << depth)