alpha clipping bug

alphabug.ipynb

alphabug.png

alphapoints.txt

1.029128626334328445e+01 1.365816287575282217e+01
1.195670482003673030e+01 1.471579988333618516e+01
1.897682175711089059e+01 1.382784831636707068e+01
1.113533517690262187e+01 1.601637670660973711e+01
1.462906854496425879e+01 1.375513889320493455e+01
1.100534935018026950e+01 1.907425742182736172e+01
1.884919710605745280e+01 1.251931919170242402e+01
1.045159564037694544e+01 1.884556815316026501e+01
1.158277314162118188e+01 1.621805205103852998e+01
1.660235416968842159e+01 1.519387455027133882e+01
1.756838227823502763e+01 1.380998327257449354e+01
1.723869420902103755e+01 1.023414275142773633e+01
1.698404619430929685e+01 1.205643537016283773e+01
1.204673219358900660e+01 1.956061924357363324e+01
1.499043599656454795e+01 1.145301772049807987e+01
1.708209028469097035e+01 1.402870211122390209e+01
1.589573166403873117e+01 1.465951259545013485e+01
1.582136241533121179e+01 1.050353084733463938e+01
1.147080242126983762e+01 1.457617246833424751e+01
1.758407826011995922e+01 1.616417827489364711e+01
1.717312085194632232e+01 1.270418505208493087e+01
1.332203009720132414e+01 1.425581912363055181e+01
1.946907894574708564e+01 1.314421552600851228e+01
1.704857801949855656e+01 1.035906345122783456e+01
1.339986530464298298e+01 1.939053117658754388e+01
1.504669045194645172e+01 1.661936061061076941e+01
1.287454403444879247e+01 1.808811930471991758e+01
1.959718858566854038e+01 1.439118605832049980e+01
1.264476504038637827e+01 1.545316648830846162e+01
1.834661710432902737e+01 1.052062362263327344e+01
1.161168727172857018e+01 1.042609481502864099e+01
1.005375702449195963e+01 1.378849222938711527e+01
1.977190244539414721e+01 1.168635731842035419e+01
1.689198869339618625e+01 1.553627001092079851e+01
1.293537450428770796e+01 1.094741669487824609e+01
1.011649833845572388e+01 1.463882930247080161e+01
1.959407900074536002e+01 1.578353082466281521e+01
1.298147190913113747e+01 1.565679636207205760e+01
1.659623645664111891e+01 1.614805175330319997e+01
1.486084931012926091e+01 1.014642950294869905e+01
1.190328905291297446e+01 1.891832213780040206e+01
1.450627033074235683e+01 1.269156576659019464e+01
1.598140358238145708e+01 1.550667220541790670e+01
1.946557544983048871e+01 1.954205825748656622e+01
1.592717374102223182e+01 1.170862929232374583e+01
1.260927308699297811e+01 1.031667428830976263e+01
1.438377320701443196e+01 1.123894736922024506e+01
1.648343788504370622e+01 1.002621532387114200e+01
1.318416688225100941e+01 1.381532057344131914e+01
1.302815156398435548e+01 1.306160001112482938e+01

diagnosis.py

import libpysal
from libpysal.cg import alpha_shapes

import numpy
import geopandas
points = numpy.loadtxt('alphapoints.txt')

## just pull in the algo line by line
from scipy import spatial
triangulation = spatial.Delaunay(coords)
triangles = coords[triangulation.simplices]
a_pts = triangles[:,0,:]
b_pts = triangles[:,1,:]
c_pts = triangles[:,2,:]
# the radii broadly look correct.
radii = alpha_shapes.r_circumcircle_triangle(a_pts, b_pts, c_pts)
radii[numpy.isnan(radii)] = 0
radii_sorted_i = radii.argsort()
triangles = triangulation.simplices[radii_sorted_i][::-1]
radii = radii[radii_sorted_i][::-1]
boundingbox = numpy.array([*xys.min(axis=0), xys.max(axis=0)])

# step through each geometry & see what changes:
shapes = (alpha_shapes.alpha_geoms((1/radii[i]) - numpy.finfo(float).eps, triangles, radii, xys) for i in range(50))

for i in range(50):
    this_shape = next(shapes)
    geopandas.GeoDataFrame(geometry=this_shape).plot(facecolor='cornflowerblue', edgecolor='k')
    plt.show()
    get_input = input()
    if get_input != '':
        break

mwe.py

#!/usr/bin/env python
# coding: utf-8

# In[1]:


import libpysal
import numpy
import geopandas
from shapely.geometry import Point, Polygon
get_ipython().run_line_magic('matplotlib', 'inline')


# In[2]:


points = numpy.loadtxt('alphapoints.txt')
points.shape


# In[3]:


w_test = libpysal.weights.Voronoi(points)


# In[4]:


w_test.n


# In[5]:


p_gdf = geopandas.GeoDataFrame(geometry=[Point(point) for point in points])


# In[6]:


regions, generators = libpysal.cg.voronoi.voronoi_frames(points)


# In[7]:


a_regions = libpysal.cg.voronoi.clip_voronoi_frames_to_extent(regions, generators, clip='ahull')


# In[8]:


ax = regions.plot(color='white', edgecolor='black')
a_regions.plot(ax=ax, alpha=0.2, color='green')
generators.plot(ax=ax, color='red')


# In[ ]: