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#### A.4.4.10 Function Layer Control

The Function layer control () is only available for the Plane, Histogram and Time plots. You can add one of these controls to the stack by using the Add Function Control () button in the control panel toolbar, or the corresponding item in the Layers menu.

Plane plot with two function layers plotted, one as a function of Horizontal axis value, and one as a function of Vertical axis value

This control has three tabs, Function, Style and Label, described below.

Function Tab

Function control Function tab

The Function tab defines the function to be plotted and has the following fields:

Independent Axis
  Which axis the independent variable varies along; options are currently Horizontal and Vertical.
Independent Variable Name
  Name of the independent variable. This is typically `x` for a horizontal independent variable and `y` for a vertical independent variable, but any string that is a legal expression language identifier (starts with a letter, continues with letters, numbers, underscores) can be used.
Function Expression
  An expression using TOPCAT's expression language in terms of the independent variable that defines the function. This expression must be standalone, it cannot reference any tables. It can however reference Global Variables.

Style Tab

Function control Style tab

The Style tab configures the plotting style. Options are:

Colour
  Colour of the line.
Thickness
  Thickness of the line in pixels.
Dash
  Dash pattern of the line - solid is the default, but various options are available.
Antialiasing
  If true, lines are antialiased, which makes them look smoother on the screen or bitmapped export images. Has no effect on vector export images (PDF, SVG, EPS).

Label Tab

Function control Label tab

The Label tab allows you to choose the text that appears in the legend. Options are:

Label
  Gives the label that will appear in the legend. By default the function expression is used, but if you want to override this you can deselect the associated Auto checkbox and enter your own value.
In Legend
  If true, an entry for this function appears in the legend, if false it does not. Note the setting of this value does not affect whether the legend itself appears, which is controlled by the Legend control.

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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