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## B.15 `plot2sky`: Draws a sky plot

`plot2sky` draws plots on the celestial sphere. This can be represented in a number of ways, controlled by the `projection` parameter; by default the view is of a rotatable sphere seen from the outside (which approximates to a tangent projection for small regions of the sky), but Hammer-Aitoff and Plate Carée projections are also available. A number of options are also provided for drawing and labelling the grid showing celestial coordinates.

Positional coordinates are specified as `lon`, `lat` pairs giving longitude and latitude in decimal degrees. By default these are represented in the output in the same, unlabelled, coordinate system. However the command can can also transform between different coordinate systems if you specify the (per-plot) view system with the `viewsys` parameter and (per-layer) data system with the `datasysN` parameter, e.g.:

       plot2sky viewsys=galactic
                layer1=mark in1=cat.fits lon1=RA2000 lat1=DEC2000 datasys1=equatorial

Content is added to the plot by specifying one or more plot layers using the `layerN` parameter. The `N` part is a suffix applied to all the parameters affecting a given layer; any suffix (including the empty string) may be used. Available layers for this plot type are: `mark`, `size`, `sizexy`, `skyvector`, `skyellipse`, `skycorr`, `link2`, `mark2`, `poly4`, `mark4`, `polygon`, `area`, `central`, `label`, `arealabel`, `contour`, `skydensity`, `skyvecfield`, `healpix`, `skygrid`.

- B.15.1 Usage
- B.15.2 Examples

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STILTS - Starlink Tables Infrastructure Library Tool Set
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