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#### A.4.12.1 Sphere Navigation

For general comments on plot navigation, see Appendix A.4.2.1. Additional configuration options are available in the Navigation tab of the Axes control.

Navigation in three dimensions with a two-dimensional screen and mouse is a bit of a challenge. However, the actions listed below should make it fairly straightforward to navigate around points in 3d space to zoom in on the regions that you are interested in. The actions are quite like for the Cube Window, but all zooming is isotropic.

Left drag
  Rotate. Rotates the view cube about its center.
Wheel
  Zoom. Spinning the mouse wheel forwards/backwards zooms the space in the view cube in/out around the cube center. The mouse position does not affect it.
Right drag (CTRL-drag)
  Zoom. Zooming up-and-right/down-and-left does just the same as spinning the mouse wheel forwards/backwards.
Center drag (SHIFT-drag)
  2d pan. Dragging with the center button pans the 3d space in the two dimensions best alighned with the plane of the screen. There is no movement in the third (mostly perpendicular to the screen) direction.
Left click
  Select. If there are plotted points near the cursor it will identify one, plot a marker on it, and activate it.

  In 3d, it's not obvious which is the nearest point to a 2d cursor, since a screen position represents a line not a point. To break the degeneracy, the point used is the one nearest the center of mass of plotted points along the line of sight represented by the cursor position. The upshot of this is that if you click on an isolated point, you'll pick that point, and if you click on a dense cluster, you'll get a point near the center (of mass) of that cluster.

Right click (CTRL-click)
  Re-center. Right-clicking identifies a position in a similar way to the left-click Select action, and then translates the plot so that point is at the center of the view cube. This means that clicking on a cluster will put that cluster in the center of the cube. If you click on an empty region, a position half way between front and back of the cube at that X/Y position will be used.

You can also manually fix the plot bounds using the Range tab of the Axes 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