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`1d_err`

, `2d_err`

, ...:
Cartesian Matching with Per-Object Errors

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

`values*`

:

`x`

: Cartesian co-ordinate #1`y`

: Cartesian co-ordinate #2`error`

: Per-object error radius`params`

:

`scale`

: Rough average of per-object error distance; just used for tuning in conjunction with bin factor`tuning`

:

`bin-factor`

: Scaling factor to adjust bin size; larger values mean larger bins

The `1d_err`

, `2d_err`

, ... matchers compare
positions in N-dimensional Cartesian space like the
`1d`

, `2d`

matchers described in
Section 7.1.6,
except that the match radius can be different for each row.
Rows are considered to match when the separation reckoned by
Pythagoras between the `x`

, `y`

, ... positions
is no larger than the sum of the two per-row `error`

values.
Matching in any number of Cartesian dimensions can be done by extending
this syntax in the obvious way.

A variant form `1d_err_q`

, `2d_err_q`

, ...
does the same thing but combines the two per-row `error`

values
in quadrature rather than by summation.
In that case the separation beween the two positions
must be no larger than *sqrt(error1 ^{2}+error2^{2})*.

The `scale`

parameter must be supplied, and should be
approximately the characteristic size of the per-object error values.
In conjunction with the `bin-factor`

tuning parameter
its value affects the performance of the match, but not the result.

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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