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#### A.4.4.8 XYArray Layer Control

The XYArray layer control () can be used to plot points, lines and error bars, but unlike the Position Layer Control it works with table cells whose values are arrays giving multiple coordinates, rather than single values. It is typically used where the value stored in each cell of a column is an array representing a whole spectrum or time series, or some related quantity (such as errors, frequencies, epochs etc). Each row of the table therefore corresponds to a full spectrum, timeseries, or other array of coordinate pairs.

Use the Layers menu item or corresponding toolbar button to add an instance to the control stack. This control is only available for the Plane plot. you can add one of these controls to the stack by using the Add XYArray Control () button in the control panel toolbar, or the corresponding item in the Layers menu.

Plane Plot window with an XYArray layer

This control is a Table Data control as described in Appendix A.4.2.2. That section explains the Subsets tab; the Position and Form tabs are described in more detail below.

Position tab of XYArray layer control

In the Position tab you have to fill in array values for the X Values and Y Values plot coordinates. The contents can be array-valued column names or expressions. For each row, the X and Y coordinates must be arrays of the same length (if they are not, nothing will be plotted for that row), though different rows may have different array lengths. To manipulate array values, some of the expression language functions in the Arrays class may be useful; for instance the expression "`sequence(512)`" produces a 512-element array with values `(0, 1, 2,..., 511)`.

TOPCAT will try to fill in the X and Y coordinates with suitable array values from the table, if it can find some. As well as array-valued columns, array-valued table parameters can be used, and are often suitable for the X axis; these can be referred to using the syntax "`param$<name>`", as explained in Section 7.3. It helps if columns are declared with fixed array sizes, where applicable.

Form tab of XYArray layer control

The Form tab lets you define how the specified data set is plotted. The list on the left gives a list of forms currently being plotted, and the panel on the right shows the detailed configuration for the currently selected form.

The available forms for an XYArray plot (select them using the Forms button) are currently

- Lines: draws a line between the X,Y positions
- Marks: draws a marker for each X,Y position
- YErrors: draws a vertical error bar at each X,Y position
- XYErrors: draws horizontal and/or vertical error bars at each X,Y position
- StatLine: draws a single line giving per-element combinations (e.g. mean) of the input array values
- StatMark: draws a marker for each per-element combination (e.g. mean) of the input array values

You can have zero or more of each form and configure them separately. The detail panel for these forms is dependent on the form itself and are described in more detail in Appendix A.4.5, but the detail panels are divided into these parts:

Shading
  The shading mode controls how points are shaded based on their chosen colour. The various options are described in Appendix A.4.6. Depending on the mode there may be more settings to fill in here.
Global/Subset Styles
  Controls the style details for the chosen form; see Appendix A.4.2.2.

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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