Match two sky catalogs within angular radius — coord

Low-level spherical catalog matching for two `sky_coord` vectors.

Usage

coord_match(x, y, max_sep, unit = "arcsec", method = "kdtree", sort = TRUE)

coord_nearest(x, y, unit = "arcsec", method = "kdtree")

x, y: `<sky_coord>` vectors.
max_sep: Maximum separation threshold. Used in [coord_match()]. [coord_nearest()] always uses `Inf`.
unit: Separation unit: `"arcsec"`, `"arcmin"`, `"deg"`, or `"rad"`.
method: Matching backend: `"kdtree"` or `"bruteforce"`.
sort: If `TRUE` (default), sort matches by `x_id`, then `sep`, then `y_id`. Set to `FALSE` to skip sorting for better performance.

Numeric matrix with columns `x_id`, `y_id`, `sep`. `sep` is returned in the same unit as `unit`.

If frames differ, `y` is transformed to the frame of `x`.

Rows are sorted by `x_id`, then `sep`, then `y_id`.

If an `x_id` has no matches, one row is returned with `y_id = NA` and `sep = NA`.