A.4.2 Plot Window Overview

Plot window

Plot windows consist of two main parts: the Plot Panel containing the actual plotted graphics (by default, at the top), and the Control Panel (by default, at the bottom). The Control Panel is where you configure what will be plotted. For a simple scatter plot it may just be a case of selecting what columns to plot against each other, but it can get quite detailed. If you want more screen space to play with, it can be helpful to float the control panel into a separate window using the Float Controls () toolbar button; you can find this button in both the main and the control panel toolbars. To unfloat the control panel, either just close the control panel window, or click the Float Controls toolbar button again. With floating controls, the window looks like the following figure.

Plot window with floated control panel

The control panel itself has two main parts: a control stack on the left containing currently active controls (represented by names and icons), and a detail panel on the right which shows information about the currently selected control. Click on one of the control entries on the left to see its details on the right. Different controls have different detail panels, but in general each one will have multiple tabs for configuring different things. You can select these by clicking on the tab names. A good way to learn about the options is to click on the different controls and their tabs to see what's available and experiment with the various options to see what happens to the plot, but all the panels and tabs are also explained in this manual. The control panel also has a toolbar at the top, used for adding and removing controls from the stack.

The control list has two types of entry:

Fixed controls:

These control the overall plot appearance. In the above figure, the fixed controls Frame (), Legend (), Axes () and STILTS () are visible.

The different fixed controls are described in Appendix A.4.3.

Layer controls:

These determine the actual data that will be plotted and what graphical form it takes; each control contributes a layer or layers to the plot. To add a layer control, use the toolbar just above; each button with a little green "+" adds a control of the corresponding type. To remove a layer control, select it and use the Remove Current Layer () button in the toolbar. You can also use the Layers menu at the top of the main window to add and remove layers.

The checkbox beside each control determines whether it is currently active; if unchecked, any plotting instructions is contains will be ignored. You can set them active or inactive by clicking on the checkboxes.

You can also drag each control up or down by dragging with the grab handle (). Layers lower down the list are plotted later (perhaps obscuring earlier one), so you can drag them up and down until you have the layers you want on top.

The different layer controls are described in Appendix A.4.4.

In the foot of the window, there are also four other small panels:

Position Panel

When the cursor is positioned over the plot itself, this reports its position in data coordinates. In some cases, such as 3-d plots, this may not be possible, in which case it's blank.

Count Panel

Displays the number of points currently plotted and the total number of points represented by the plot. The total (the second figure) is the number of positions in all the plotted data sets, and the current number (the first figure) excludes those in subsets not currently plotted and those outside the bounds of the visible plot.

Navigation Help

Shows some reminders for what different mouse gestures do. Little icons are supposed to represent clicking and dragging different mouse buttons and the mouse wheel. Note the content changes according to where the mouse is on the plot, since that affects navigation behaviour. For more information see Appendix A.4.2.1. Clicking on the button will make this panel go away.

Progress Bar

If something slow is happening you may see a progress bar at the bottom of the screen while you wait. Unless you are plotting several million points, you may not see this at all. For slow data loads, this will always be displayed. For actions like actually drawing the plot and turning a blob into a subset selection you can choose whether progress is shown using the Show Plot Progress () button in the toolbar. It's nice to know that something's going on, but it can be distracting; displaying progress also slows the plot down a bit.

The main toolbar at the top of the window contains the following actions (repeated in the menus):

Float Controls

Puts the Control Panel into a floating window rather than at the bottom of the plot window, as described above. Once floating, the control panel can be joined back to the main window by clicking this button again.

Draw Subset Blob

Allows you to draw a region on the screen defining a new Row Subset. When you have finished drawing it, click this button again to indicate you're done. See Appendix A.4.2.3.3 for more details.

Subset From Visible

Defines a new Row Subset consisting of only the points which are currently visible on the plotting surface. See Appendix A.4.2.3.1 for more explanation.

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, or by redefining a subset, the plot is not automatically redrawn. Clicking this button redraws the plot taking account of any changes to the table data.

Rescale

Rescales the axes of the current plot so that it contains all the data points in the currently selected subsets. By default the plot will be initially scaled like this, but it it may have changed because of changes in the subset selection or from zooming in or out.

Lock Axes

Usually, when the data plotted has changed significantly, the axes are automatically rescaled so that all the points are visible. The application makes a guess about when it's a good idea to do this automatic rescaling. If you don't want it to auto-rescale, set this toggle button, and it won't rescale unless it really has to. This is not available for the Sky Plot.

Lock Aux Range

This controls when the Aux data range, sometimes used to colour data points (see the Aux Axis Control), is updated to match the currently visible data. By default, the range is updated dynamically as the plot changes, for instance when you pan or zoom it, so that the data range covered by the aux colour ramp matches the range of the currently visible data. But if this checkbox is checked, then the range is frozen to the current value. Data-sensitive updates to the aux range will then not be performed until it's unchecked again.

It also affects some other dynamic ranging calculations such as Auto-Scale sizes for plot forms Size, SizeXY, Vector, SkyVector, Ellipse, SkyEllipse, XYCorr and SkyCorr.

Sketch Frames

If selected causes intermediate "sketch" frames to be drawn when navigating around very large plots. For plots that take a long time (at least a non-negligable fraction of a second) to draw, if this option is selected then when navigating around it will paint intermediate frames based on a subsample of the data rather than painting the whole plot at every step. This can result in a somewhat flickering appearance, but it means that frame updates happen more frequently, so it's a bit more responsive.

Show Plot Progress

If selected a progress bar at the bottom of the window is active when large (slow) plots are in progress. This can be useful if you are navigating round a very large plot so that you can see something is happening rather than the application apparently just doing nothing. On the other hand a flickering progress bar can be distracting. Updating the progress bar may also slow the plot down a little.

Export Plot

Allows you to save the plot in a variety of graphics formats using the Plot Export window.

The window menus offer an alternative way to perform the actions available from the toolbar described above. They also provide some additional options:

Layers menu

This menu repeats the options available in the toolbar from the Control Panel at the bottom of the window; each one adds a new Layer Control of one of the available types to the stack, or Removes () the currently selected control.

Export menu

This menu provides some options for exporting graphics and data from the plot to external contexts:

Export Plot

Saves the visible plot in an image format; see Appendix A.4.2.5.

STILTS Command Window

Displays a command which can be executed from outside TOPCAT to reproduce the currently visible plot; see Appendix A.4.3.4.

Layer Data Import

Layer Data Save

These two sub-menus may or may not contain options. Some plotted layer types (for instance 1d or 2d histograms) generate table data as part of their calculations that can be exported separately. If one of these layers is currently plotted, then options may appear in these menus. The Import options retrieve the table and add it to the list of tables currently loaded in TOPCAT; the Save options can write the data directly to disk using one of the supported table formats.

The following subsections explain some other features common to all the plotting windows.

• A.4.2.1 Navigation
• A.4.2.2 Table Data Layer Controls
• A.4.2.3 Defining Subsets Graphically
• A.4.2.3.1 Subset from Visible
• A.4.2.3.2 Algebraic Subset From Visible
• A.4.2.3.3 Draw Blob Subset
• A.4.2.3.4 Draw Algebraic Subset
• A.4.2.4 Distance Measurement
• A.4.2.5 Plot Export Window