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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 in the interior of the sphere, at a distance from the centre given by the value of the radial coordinate.

The following buttons are available on the toolbar:

Split Window
Allows the dataset selector to be resized by dragging a separator between it and the plot area. Good for small screens.
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.
Configure Axes
Pops up a dialogue to allow manual configuration of axis ranges and labels - see Appendix A.4.1.2. The only configurable axis range is the upper limit of the radial axis.
Export as EPS
Pops up a dialogue which will write the current plot as an EPS file. In general this is a faithful and high quality rendering of what is displayed in the plot window. However, if plotting is being done using the transparent markers, it won't come out right since transparency cannot be represented in PostScript; the markers will be rendered as if they were opaque. Currently, if there are many points being plotted, this can result in a rather large output 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 of the current plot so that it contains all the data points in the currently selected subsets. By default the plot will be scaled like this, but it it may have changed because of changes in the subset selection.
Reorient
Reorients the axes of the current plot to their default position. This can be useful if you've lost track of where you've rotated the plot to with the mouse. This also resets the zoom level to normal if you've changed it.
Stay Upright
Toggle button which when selected ensures that the north pole (latitude = +90 degrees) is oriented vertically on the screen at all times. By default this is on.
Grid
Toggles whether the spherical wire frame bounding the plot is drawn or not.
Draw Subset Region
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. The subset will include points at all depths in the viewing direction which fall in the region you have drawn. See Appendix A.4.1.5 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.4.1.5 for more explanation.

The following additional item is available as a menu item only:

Antialias
Toggles whether the axes and their annotations are drawn antialiased. Antialiased lines are smoother and generally look more pleasing, especially for text at a sharp angle, but it can slow the rendering down a bit.

The Dataset Toolbar contains the following options:

/ Add/Remove dataset
See Appendix A.4.1.1.
/ Add/Remove auxiliary axis
See Appendix A.4.1.4.
Toggle tangential error bars
When activated, an additional column selector appears in the dataset panel to the right of the Longitude and Latitude selectors, along with its own unit selector. You can fill this in with an isotropic error value representing the radius of a small circle associated with the selected points, in units of arcsec, arcmin, degrees or radians. This will cause 2-d error bars to be plotted. You can configure their appearance (e.g. crosshairs, ellipses, rectangles, ...) using the style editor in the usual way. See Appendix A.4.1.3 for more information.
Toggle radial error bars
Switches radial error bars on and off. See Appendix A.4.1.3.

You have considerable freedom to configure how points are plotted including the shape, colour and transparency of symbols and the representation of errors if used. This works exactly as for the Cartesian 3D plot as described in Appendix A.4.5.1.


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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