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#### 4.3.1 `skysim`

Usage: `:skysim:<nrow>`

Generates a simulated all-sky star catalogue with a specified number of rows. This is intended to provide crude test catalogues when no suitable real dataset of the required size is available. In the current implementation the row count, is the only parameter, so the specification "`:skysim:5e6`" would give a 5 million-row simulated catalogue. The row count may be given as a plain integer (`1000`), or with embedded underscores (`1_000`), or in exponential format (`1e3`).

The current implementation provides somewhat realistic position-dependent star densities and distributions of magnitudes and colours based on positionally averaged values from Gaia EDR3. The source positions do not correspond to actual stars. The columns and the statistics on which the output is based may change in future releases.

Example:

    :skysim:6
    +-----------+------------+------------+------------+-----------+-----------+------------+
    | ra        | dec        | l          | b          | gmag      | rmag      | b_r        |
    +-----------+------------+------------+------------+-----------+-----------+------------+
    | 266.7702  | -32.689117 | -3.044958  | -2.217145  | 18.168278 | 16.03555  | 1.046624   |
    | 276.83398 | 8.132022   | 37.491447  | 9.031909   | 18.331224 | 18.786451 | 1.4425725  |
    | 92.04118  | 23.79857   | -173.02219 | 1.7854756  | 16.743847 | 15.623316 | 1.690048   |
    | 271.08215 | -5.2012086 | 22.848532  | 8.022958   | 21.538874 | 17.782997 | 2.1645386  |
    | 298.83368 | 31.401922  | 67.75605   | 1.6348709  | 20.145718 | 17.728764 | 1.1521724  |
    | 204.9299  | -77.07571  | -54.29949  | -14.464215 | 19.044079 | 20.277771 | 0.92987275 |
    +-----------+------------+------------+------------+-----------+-----------+------------+

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TOPCAT - Tool for OPerations on Catalogues And Tables
Starlink User Note253
TOPCAT web page: http://www.starlink.ac.uk/topcat/
Author email: m.b.taylor@bristol.ac.uk
Mailing list: topcat-user@jiscmail.ac.uk