Next Previous Up Contents
Next: 2d_ellipse: Cartesian Matching of Elliptical Regions
Up: Match Criteria
Previous: 2d_cuboid, ...: Cuboid Cartesian Matching

#### 7.1.9 `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(error12+error22).

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.

Next Previous Up Contents
Next: 2d_ellipse: Cartesian Matching of Elliptical Regions
Up: Match Criteria
Previous: 2d_cuboid, ...: Cuboid Cartesian Matching

STILTS - Starlink Tables Infrastructure Library Tool Set