How to set varying alpha parameter in python alphashape

Question

Environment

• Alpha Shape Toolbox version: 1.3.1
• Python version: 3.9.12
• Operating System: windows 10 19044.1826

Questions

I tried to understand how to set a varying Alpha parameter from this tutorial but with no vail.

Here's the code

import os
import sys
import pandas as pd
import numpy as np
from descartes import PolygonPatch
import matplotlib.pyplot as plt
sys.path.insert(0, os.path.dirname(os.getcwd()))
import alphashape

points_2d = [(0., 0.), (0., 1.), (1., 1.), (1., 0.),(0.5, 0.25), (0.5, 0.75), (0.25, 0.5), (0.75, 0.5)]

alpha_shape = alphashape.alphashape(
    points_2d,
    lambda ind, r: 1.0 + any(np.array(points_2d)[ind][:,0] == 0.0))
alpha_shape

My questions lie in this line of code:

lambda ind, r: 1.0 + any(np.array(points_2d)[ind][:,0] == 0.0)

• Is ind the iterator that loops through the points array?
• From the source file, it seems that r is circumradius of the simplex. How is this value obtained and used?
• What does [:,0] mean?

Also, more examples on setting varying alpha parameter would be highly appreciated, e.g. based on point density, or by passing in an alpha parameter list.