link.alpha Function (GPL)

Syntax

link.alpha(<algebra>, radius(<numeric>))

or 

link.alpha(<binning function>, radius(<numeric>))

or 

link.alpha(<statistic function>, radius(<numeric>))

<algebra>. Graph algebra, such as x*y. Refer to Brief Overview of GPL Algebra for an introduction to graph algebra.

<numeric>. A numeric value indicating the This is required.

<binning function>. A binning function.

<statistic function>. Another statistic function. The result of the embedded statistic is used to calculate link.alpha.

Description

Calculates the alpha shape for the values. This function is typically used with the edge graphic element. The alpha shape is a generalization of the convex hull. If the radius is sufficiently large, the result is a convex hull. For smaller radius values, the shape shrinks and becomes concave. It also may not connect or contain some data values.

Examples

Figure 1. Example: Creating an alpha shape graph
ELEMENT: edge(position(link.alpha(x*y, radius(50))))

Statistic Functions

See GPL Functions .