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#### A.4.6.6 Aux Mode

Example Aux shading mode plot

Aux mode selection

The Aux shading mode () colours each point according to the value of an additional data coordinate. The point colours then represent an additional dimension of the plot. There is an additional option to draw the points with a fixed transparency.

The shading is done using the shared colour map. This colour map is used by all currently visible Aux, Weighted, Grid and SkyDensity layers. When at least one such layer is being plotted, the Aux Axis control is visible in the control panel, which allows you to configure the colour map, range, ramp display etc.

The options are:

Aux
  The auxiliary coordinate data values. Fill this in with a column name or expression from the table just like for a positional coordinate.
Opaque Limit
  Determines transparency of the points. By default, they are fully opaque, but if you slide the slider to the right, they will become progressively more transparent.

Exporting: Transparent points are rendered in PDF output, though the transparency levels may not be exactly the same as on the screen. This can be fixed by using the Force Bitmap option in the Plot Export dialogue. For PostScript, transparent points are rendered as opaque. You can use Force Bitmap with PostScript which will get transparency right for this layer, but then any earlier layers will be completely obscured.

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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