Rows in the output catalogue

Figure: Rows in paired catalogues

Figure  illustrates the result of pairing two catalogues, with a set of corresponding rows in the catalogues identified. There are a number of options for the set of rows to be included in an output catalogue generated from such a pairing. The various alternatives available in catpair are described below.

COMMON

(often called the `inner join' in relational database terminology). Only the objects common to both catalogues are retained; that is, only the paired objects are retained. This option might be used when pairing a list of target stars with a standard catalogue.

PRIMARY

(often called the `outer join' in relational database terminology). All the rows in the primary catalogue are retained. For paired objects fields corresponding to the secondary will contain actual values, for unpaired objects they will contain null values. The corresponding case of retaining all the rows in the secondary can be realised by regarding the primary as the secondary and vice versa. This option might also be used when pairing a list of target stars with a standard catalogue.

MOSAIC

The output catalogue contains a row for every paired row in the input catalogues and also a row for every unpaired row in either catalogue. This is option useful for constructing a mosaic of a larger area of sky from several slightly overlapping catalogues.

PRIMREJ

Only the unpaired objects in the primary catalogue are retained. The corresponding case of retaining all the unpaired rows in the secondary can be realised by regarding the primary as the secondary and vice versa. This option might be used in proper motion studies.

ALLREJ

The output catalogue contains a row for all the unpaired objects in either catalogue. This option might also be used in proper motion studies.