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#### A.4.5.11 Polygon Form

The Polygon () form plots filled or outlined polygons with an arbitrary number of vertices. The first vertex is given in the Position Layer Control's Position tab, and the others are given in the Coordinates box within the Form tab.

Example Polygon plot

Polygon form configuration panel

The configuration options are:

Shading mode
  See Appendix A.4.6.
Other Points
  Array of coordinates giving the polygon vertices excluding the first vertex, which is given by the main Position. These coordinates are given as an interleaved array, e.g. `(x2,y2, x3,y3, x4,y4)`. Expression language functions including `array(a,b,c,...)` from the Arrays class, and `parseDoubles(txt)` from the Conversions class, can be useful here. Although the first coordinate pair is supposed to be given in the Position tab and not in this array, if it's more convenient to repeat the first pair here it doesn't usually affect the plot's appearance.
Use Position
  Determines whether the basic positional coordinates for the plotted row are included as one of the polygon vertices or not. The polygon has N+1 vertices if this value is set, or N if it is not, where N is the number of vertices supplied by the Other Points array. If unset, the reference position is ignored for the purposes of drawing the polygon.
Polygon Mode
  Defines how the polygon is drawn. Options are
  - `outline`: draws a line round the outside of the polygon
  - `fill`: fills the interior of the polygon
  - `cross`: draws a line round the outside of the polygon and lines between all the vertices
Fast
  Determines whether speed is favoured over accuracy when drawing polygons. In some cases unchecking this will give visually better results, and in some cases checking it will speed up plotting. In other cases, the setting will make no difference to either. It may be necessary to unset it when filling polygons that may be re-entrant.

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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