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Questions tagged [alpha-shape]

Alpha shapes are a generalization of "convex hull" and also formalize hulls that are not convex.

The original paper is:

Edelsbrunner, Herbert; Kirkpatrick, David G.; Seidel, Raimund (1983), "On the shape of a set of points in the plane", IEEE Transactions on Information Theory, 29 (4): 551–559, doi:10.1109/TIT.1983.1056714.

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get coordinate of points where a line crosses a polygon

I would like to find the points where a line intersects with a polygon. I obtain this polygon using a concave outline calculation from this thread. import alphashape from shapely.geometry import LineString import matplotlib.pyplot as plt from…
Alejandro
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Is there a function in CGAL that removes the holes from a alphashape?

Im trying to remove the holes from a alphashape to get a similar function as MATLABs boundary.m. The code Im using is basically the example from CGALs documentation. Imageexample with alphashape to the left and boundary to the right:
Viktor
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Alpha Shapes in 3D - Follow Up

Problem I am trying to implement Edelsbrunner's Algorithm for the alpha shape of a 3D point cloud in python as presented in this SO post. However, I'm having trouble plotting results. Half my sphere looks good, and the other half garbled. I suspect…
adam.hendry
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Problem to diplay a 3d mesh using alphahull >0 with plotly in jupyter notebook

I tried the following example 3D Mesh example with AlphaNull to test alphahull but my jupyter notebook display just something blank. When I set alphahull=5, the display is blank: But when i set alphahull = 0, it works: and when i set alphahull =…
Absynthe
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Alphashape and PolygonPatch: basic example doesn't work. Why?

I am trying to use the package Alphashape from here. Although I correctly copied and pasted the example in the initial pages, I get the following error: File "/anaconda3/lib/python3.8/site-packages/descartes/patch.py", line 87, in PolygonPatch …
Mik Kim
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How to set varying alpha parameter in python alphashape

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…
David H. J.
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Contour detection in 2D scatter plot

I am looking for an algorithm, that is able to detect the contour of the attached scatter plot (only for the area y<4, y>4 is not relevant for me). I need that contour to filter out the points that are on it to make some measurements. Background:…
Fabian
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Efficiently Filtering Triangles within an Alpha Shape in CGAL

I am currently working on a project that involves processing a large number of points using CGAL's Constrained Delaunay Triangulation and Alpha Shape functionalities. However, I am facing performance issues when filtering triangles that lie within…
Dawid
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Why is the alpha shape calculating the same volume and the convex hull volume?

I am using the CGAL library of the C++ language to calculate the volume of the alpha shape. I have completed it, but why is its volume the same as the volume calculated by the convex hull. this convex hull's code Polyhedron…
kasi
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How to removing vertices from 2D alpha shape in CGAL when alphaShape::remove is private?

I am working with CGAL to manipulate 2D alpha shapes in C++, and my objective is to simplify an alpha shape by removing certain vertices based on specific criteria. However, I encountered a challenge when attempting to remove vertices using…
Dawid
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Alphashape produces unexpected multipolygons for big point clouds

I'm using: Alpha Shape Toolbox version 1.3.1; Python version 3.10.9; Operating System Windows 10. While making an alphashape for a group of 2D points, unexpected results with a multipolygon are obtained. I expected in each case a single…
Daiva
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how to calculate one concave-hull polygon using alphashape?

I'm using the alphashape toolbox (alphashape 1.3.1) to calculate a concave hull polygon for a set of points and I'm getting one convex polygon when alpha=6 and two polygons when alpha=7. xy_p = [(0.2, 0.1), (0.3, 0.1), (0.4, 0.1), (0.4, 0.2), (0.4,…
New programmer
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How to create Isopolygon using python?

I have a set of points of a location. I am trying to create an isoline using those points. In order to generate isolines I used convex hull and alphashape which is creating kind of box shaped or straight cut line kind of polygon structure like…
data en
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How to understand a lambda function in a library

Question Here's a function to calculate alphashape of a set of points. It's from the documentation of the library '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 =…
David H. J.
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Is there any command which will give me a alpha shape based on multipoint geometry?

Good Day Everyone, I am having the clustered geodata which has a multipoint as a geometry. I am able to create convex hulls, using geopanda's method convex_hull. But somehow I was not able to find a similar command for creating an alpha shape. Or…
Avto Abashishvili
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