A.4.6 Spherical Plot

Spherical plot window

Spherical plot window

The spherical plot window draws 3-dimensional scatter plots of datasets from one or more tables on spherical polar axes, so it's suitable for displaying the position of coordinates on the sky or some other spherical coordinate system, such as the surface of a planet or the sun. You can display it using the Sphere () button in the Control Window's toolbar.

In most respects this window works like the 3D Plot window, but it uses spherical polar axes rather than Cartesian ones, You have to fill in the dataset selector at the bottom with longitude- and latitude-type coordinates from the table. Selectors are included to indicate the units of those coordinates. If TOPCAT can locate columns in the table which appear to represent Right Ascension and Declination, these will be filled in automatically. If only these two are filled in, then the points will be plotted on the surface of the unit sphere - this is suitable if you just want to inspect the positions of a set of objects in the sky. You can optionally fill in the Radius selector as well. If you do this, then points will be plotted on the interior of the sphere, at a distance from the centre given by the value of the radial coordinate.

Rotation, subset creation, fogging, marker customisation and toolbar actions are all as for the Cartesian 3D plot window - see Appendix A.4.5.

Zooming is also possible. You can zoom in around the centre of the plot so that the viewing window only covers the middle. This resembles the Axis Zoom in some of the 2-d plots, but in this case the active region is to the right of the plot where the legends appear. Drag the mouse down to zoom in or up to zoom out on this part of the window. When zoomed you can use the Subset From Visible () toolbar button to define a new Row Subset consisting only of the points which are currently visible. See Appendix A.4.1.3 for more explanation.