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A.4.2 Histogram

Histogram Window

Histogram Window

The histogram window lets you plot histograms of one or more columns or derived quantities. You can display it using the Histogram () button in the Control Window's toolbar.

You select the quantity or quantities to plot using the dataset selector at the bottom of the window. You can configure the axes, including zooming in and out, with the mouse or manually as described in Appendix A.4.1.2.

The Bin Placement box below the main plot controls where the bars are drawn. Select the horizontal range of each bar using the Width entry box - either type in the value you want or use the tiny up/down arrows at the right to increase/decrease the bin size. The Offset checkbox on the left determines where the zero point on the horizontal axis falls in relation to the bins; if the box is checked then zero is in the centre of a bin, and if it's unchecked then zero is on a bin boundary.

The following buttons are available on the toolbar:

Export as EPS
Pops up a dialogue which will write the current plot as an EPS file.
Export as GIF
Pops up a dialogue which will output the current plot to a GIF file. The output file is just the same as the plotted image that you see. Resize the plotting window before the export to control the size of the output GIF.
Rescale
Rescales the axes so that the width and height are sufficient to accommodate all the non-zero bars in the histogram for all the currently selected datasets. By default the plot will be scaled like this, but it it may have changed because of changes in the subset selection or from zooming in or out.
Rescale X
Rescales the horizontal axis to accommodate all the currently plotted bars. The vertical axis scaling is not changed.
Rescale Y
Rescales the vertical axis to accommodate all the currently plotted bars. The horizontal axis scaling is not changed.
Configure Axes
Pops up a dialogue to allow manual configuration of axis ranges and labels - see Appendix A.4.1.2.
Grid
Toggles whether a grid is drawn over the plotting surface or not.
Cumulative Plot
Toggles whether the histogram should be normal or cumulative. Normally the height of each bar is determined by counting the number of points which fall into the range on the X axis that it covers. For a cumulative plot, the height is determined by counting all the points between negative infinity and the upper bound of the range on the X axis that it covers.
Log Y Axis
Toggles whether the Y axis is scaled logarithmically or not.
Replot
Redraws the current plot. It is usually not necessary to use this button, since if you change any of the plot characteristics with the controls in this window the plot will be redrawn automatically. However if you have changed the data, e.g. by editing cells in the Data Window, the plot is not automatically redrawn (since this is potentially an expensive operation and you may not require it). Clicking this button redraws the plot taking account of any changes to the table data.
Subset From Visible
Defines a new Row Subset consisting of only the data in the bars which are visible in the current plot. See Appendix A.4.1.3 for more explanation.

You have considerable freedom to configure how the bars are drawn; controlling this is described in the following subsection.


Next Previous Up Contents
Next: Histogram Style Editor
Up: Graphics Windows
Previous: Exporting Graphics

TOPCAT - Tool for OPerations on Catalogues And Tables
Starlink User Note 253
TOPCAT web page: http://www.starlink.ac.uk/topcat/
Author email: m.b.taylor@bristol.ac.uk