7.1.1 sky: Sky Matching

matcher=sky values*='<ra/degrees> <dec/degrees>'
            params='<max-error/arcsec>'
            tuning='<healpix-k>'

values*:

• ra/degrees: Right Ascension
• dec/degrees: Declination

params:

• max-error/arcsec: Maximum separation along a great circle

tuning:

• healpix-k: Controls sky pixel size. Legal range 0 - 29. 0 is 60deg, 20 is 0.2".

The sky matcher compares positions on the celestial sphere with a fixed error radius. Rows are considered to match when the two (ra, dec) positions are within max-error arcseconds of each other along a great circle.

In fact this matching is not restricted to equatorial coordinates - the ra and dec parameters may represent any longitude-like and latitude-like coordinates in degrees, since the spherical geometry for the matching is unchanged under such transformations.