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A.4.5.5 SkyVector Form

The SkyVector form () plots directed lines from the data position given relative offsets to longitude.cos(latitude) and latitude on the celestial sphere. The plotted markers are typically little arrows, but there are other options.

In some cases such delta values may be the actual magnitude required for the plot, but often the vector data represents a value which has a different magnitude or is in different units to the positional data (for instance proper motions). As a convenience for this case, the plotter can optionally scale the magnitudes of all the vectors to make them a sensible size (so the largest ones are a few tens of pixels long). This scaling can be adjusted or turned off using the Scale and Auto Scale options below.

Example SkyVector plot

Example SkyVector plot

SkyVector form configuration panel

SkyVector form configuration panel

The configuration options are:

Shading Mode
See Appendix A.4.6.
Delta Longitude
Change in the longitude coordinate represented by the plotted vector. The supplied value is (if not auto-scaled) an angle in degrees, and is considered to be premultiplied by cos(Latitude).
Delta Latitude
Change in the latitude coordinate represented by the plotted vector. The supplied value is (if not auto-scaled) an angle in degrees.
Arrow
Arrow shape selected from a range of options.
Scale
Changes the factor by which all vector sizes are scaled. If the arrows are too small, slide it right, if they are too big, slide it left. The slider scale is logarithmic. Alternatively, enter a fixed value in the text field.
Auto Scale
If selected, this option will determine the default arrow scale size from the data - it will fix it so that the largest arrows are a few tens of pixels long by default. That scaling can then be adjusted using the Scale slider. If unselected, then the default position of the Scale slider corresponds to the actual values in degrees given by the submitted Delta Lon/Lat coordinates.


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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