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#### A.4.4.5 Healpix Layer Control

The Healpix layer control () is available from the Sky Plot Window for plotting tables that represent HEALPix maps on the celestial sphere. You can add one of these controls to the stack by using the Add HEALPix Control () button in the control panel toolbar, or the corresponding item in the Layers menu.

Each row in the table must represent a single healpix tile, and a value from that row is used to colour the corresponding region of the sky plot. The resolution (healpix order) of the input table is supplied or may be guessed in order to do the plot, but the plot may be drawn at a degraded order (bigger pixels) if required.

Note this is different from the SkyDensity form, which takes a table containing sky positions, and represents that as a density map on the healpix grid by gathering the rows up into bins. The control described here works on a table for which that binning has already been done, for instance as a prepared sky map data product, by exporting from a SkyDensity layer, or by executing a suitable (GROUP BY healpix_index) database query.

Sky Plot Window with a Healpix layer

This control has two tabs, Data and Style.

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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