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#### A.4.2.1 Navigation

All the plot windows are interactive, and you can navigate around them using the mouse buttons. For most plot types the left and right buttons and the mouse wheel do something; in 3d plots the middle button is used as well.

The details of what mouse actions do what depend on which plot window you are using, and they can also be configured to some extent using the Navigation tab in the Axes fixed control in the control stack. However, as a rule, the actions when used on the body of the plot are these:

Left drag
  Drags the plot around. Where possible, the same plot position stays under the cursor as you drag. In 2d this pans the plot left/right/up/down, and in 3d it rotates it.
Right drag
  Stretch zoom. Dragging up/down stretches/squashes the plot vertically, and dragging left/right stretches/squashes it horizontally. The zoom is centered on the position where you start the drag from, so that data position stays in the same place on the screen. In 3d, the zoom is along the two plot directions most closely aligned with the plane of the screen.
Middle drag
  Frame zoom. Dragging right-and-down or right-and-up drags out a frame; when the button is released, the plot will be zoomed in to cover area enclosed by the frame. Dragging left (and up or down) does something like the opposite, you can zoom out using a similar (though not quite the same) mechanism.
Mouse wheel
  Spinning the mouse wheel forwards/backwards will zoom in/out. In 2d the zoom is around the current position of the mouse, and in 3d it is (usually) around the center of the view cube.
Left click
  Identifies a point. If there is a plotted point near the cursor, it will plot a marker on it and activate it. If you click on an empty bit of the plot, any existing activated point will be removed, otherwise nothing will happen.

In the 2d plot types, you can pan or zoom in just one direction by using the same actions outside of the plot itself. If you do a pan/zoom action to the left of the Y axis, it will pan/zoom only vertically, and if you do it below the X axis, it will do it only horizontally.

Most of these actions give you some visual feedback on the screen, showing a rectangle or some arrows to give you a clue what you're doing. If you find that distracting, you can turn it off using the Plot|Show Navigation Graphics () menu item.

Navigation help panel at the bottom of plot windows

In each plot window there is a row at the bottom of the window giving hints on the currently available navigation actions. The little icons are each supposed to represent either a click () or a drag () with one of the three buttons pressed, or a wheel spin (), and are followed by a short description of what it will achieve. Note these hints change according to where the mouse is currently positioned on the screen. Moving the button over this panel will give you some help on the help. Clicking the button will make the line disappear, and you can bring it back with the Window|Show Navigation Help () menu item. The button will bring up a help window specific to the navigation in this window.

If you are using a mouse with fewer than three buttons or no wheel, the following subsitute gestures can usually be used:

Left button
  If you only have one button, this is it.
Right button
  If you only have one button, you can use it with the CTRL key.
Middle button
  If you only have one button, you can use it with the SHIFT key. If you have two buttons, sometimes pressing them both at once will work.
Wheel
  Often a wheel action can be simulated on a trackpad by moving two fingers together up or down.

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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