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Questions tagged [concave-hull]

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Concave Hull of subset 2D Points of fixed area that maximizes contained points

I have a set of 2D points, and I'd like to find a subset of those points from which the concave hull (or alpha-shape of a specific alpha) is below a specific threshold, but maximizes the number of points contained in the subset. Any ideas? Thanks
Adrien Nivaggioli
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ahull_track issue: 'could not find function "psp"'

I've been working with the R library alphahull for a few days now. As I'm trying to get the results as sf polygons, I'm following the recommandation here to use ahull_track, as that returns geom_path objects. However, when I try it, I run into this…
Laurent
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lwpoly_from_lwlines error on PostGIS ST_ConcaveHull function call

I'm getting this error on the ST_ConcaveHull function call and I don't know how to solve it. This is the content of my example table (inte1: text, geom_pol:…
AGL
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Is there a concave-hull algorithm where points to be excluded can be specifed?

So I have a list of points (2d) that should be inside a polygon, and a second list of points that should be outside the polygon. I want to find the polygon that encloses the "inside" points while excluding the "outside" points. The resulting polygon…
Clumsy cat
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3D concave hull algorithm (alpha shapes 3), cannot use CGAL

does anyone know of GPL (preffrably MIT) code for computing a concave hull of a 3D point set. I know there are functions in CGAL for doing this but I cannot use CGAL atm. If possible a MIT implementation would be nice or even GPL for a proof of…
lfgtm
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How to use triangulate from the library triangle in python

I want to detect the boundary of my set of points. I tried Delaunay triangulation from scipy spatial, but I get this: And when I perform alpha shape from those triangles, I can't get the boundary of the set of points. So I think that I should use…
mee
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make polygons from points extracted by concave hull

I would like to make a file including polygon or lines from boundary points extracted from point cloud by concave hull method as shown in below page. http://ait-survey.com/wp-content/uploads/2015/08/concave_hull_polygon1.png Boundary points are 3D…
LenItsuki
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Get concave hull in mapKit

Using Swift and apple mapKit I would like to calculate the concave hull from gps coordinates. I have an array of CLLocation (latitude, longitude) defining a Polyline. For a route geofencing I calculated for each 2d point in the polyline all possible…
masterWN
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Creating 3D Alpha Shapes in CGAL and the visualization

I am a new CGAL user with basic C++ experience, trying to find the 3D Alpha shapes of a set of points. I am using the ex_alpha_shapes_3 example code, and then using the instructions in saving CGAL alpha shape surface mesh for visualization of the…
Vahid
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Detecting "concave hull" on map image

I'm developing the open-source JavaScript plugin for Waze -- well-known free GPS navigator -- specifically for online editor. The idea of this userscript is to make it possible to quickly select large uniform colored map areas to convert them to…
WASD42
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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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Seg Fault raised by Shapely Concave Hull

When I attempt to create a concave hull using the below 8 points I get a seg fault. Excluding the second last point allows it to work however, and that point works by itself. It seems to be some kind of collinearity issue. from shapely import…
Eye4got
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How to compute a continuous border of concave hull (boolean matrix)?

This is an example boolean matrix I'm talking about. I have already compute a concave hull shown below: [[0,0,0,0,0,0,0,0,0,0], [0,0,0,0,1,0,0,0,0,0], [0,0,0,0,0,0,0,0,0,0], [0,0,1,0,0,0,0,0,0,0], [0,0,0,0,0,0,0,1,0,0], [0,0,0,0,0,0,0,0,0,0], …
Carl
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Python equivalent of JTS ConcaveHullOfPolygons

The latest version of JTS implements an algorithm that computes a concave hull of the input polygons, which guarantees the input polygons are contained in the result hull. All of the pythonic concave hull implementations i've seen work with points…
krezno
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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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