Selection Commands

Presently there are no commands oriented to find a single record from a catalogue and to show it with an appropriate appearance like a mask. DIRA2 is oriented to statistical search and produces files containing data selected from original catalogues. The output can be directed on the screen, but there are not labels or titles of the values found. This allows to have tables files that can be reused in DIRA2 or that can be read from personal programs, but force the user to remember what fields he selected. The Personal Data Base is a tool that minimizes this work, the user must remember that the typical output is a file.

DIRA2 is not the best tool if the user wants to know a unique data like the Magnitude of the Polar star, but this package works well if he needs to retrieve sets of data like the galaxies with magnitude greater than 18.3 in a given sky zone. The user can set constraints on all the catalogues fields, or on functions of these. The astronomical coordinates are peculiar fields in the catalogues; some format normalization are required in the data, and the input of constraints on coordinate uses appropriate forms. DIRA2 works faster, searching objects by coordinate constraints, when the catalogues are sorted in a coordinate. The simplest search command are:

Returns all the objects in a catalogues that comply with constraints on fields and/or on sky coordinates.

Like DB_SELECT, but it search objects that are inside a sky region defined by center field and size.

Returns the number of objects that comply with the constraints

With these command the user can get data from public database, or from PDB, in a simple way. The query language used in these, and in the following commands, is explain in the section .

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