chi_shapes

     set chi_shapes fraction <value>
     unset chi_shapes

The concave hull filter creates χ-shapes defined by a characteristic length chi_length. If no chi_length variable has been set, it chooses a value equal to a fraction of the longest edge in the bounding polygon (the convex hull). The fraction defaults to 0.6 but can be changed using this command. Choosing a value of 1.0 will reduce the resulting hull to the convex hull. Smaller values will produce increasingly concave hulls. See concavehull. The unset chi_shapes command restores the fraction to 0.6 and undefines the chi_length variable.