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#### 7.1.7 `2d_anisotropic`, ...: Anisotropic Cartesian Matching

    matcher=2d_anisotropic values*='<x> <y>'
                           params='<error-in-x> <error-in-y>'
                           tuning='<bin-factor>'

> `values*`:
>   - `x`: Cartesian co-ordinate #1
>   - `y`: Cartesian co-ordinate #2
> `params`:
>   - `error-in-x`: Axis length of error ellipse in Cartesian co-ordinate #1 direction
>   - `error-in-y`: Axis length of error ellipse in Cartesian co-ordinate #2 direction
> `tuning`:
>   - `bin-factor`: Scaling factor to adjust bin size; larger values mean larger bins

The `2d_anisotropic` matcher compares positions in 2-dimensional Cartesian space using an anisotropic metric. Rows are considered to match if their (`x`,`y`) positions fall within an error ellipse with axis lengths `error-in-x`, `error-in-y` of each other. This kind of match will typically be used for non-'spatial' spaces, for instance (magnitude,redshift) space, in which the metrics along different axes are not related to each other.

Matching in any number of dimensions of Cartesian space using an anisotropic metric can be done by extending this syntax in the obvious way.

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STILTS - Starlink Tables Infrastructure Library Tool Set
Starlink User Note256
STILTS web page: http://www.starlink.ac.uk/stilts/
Author email: m.b.taylor@bristol.ac.uk
Mailing list: topcat-user@jiscmail.ac.uk