area compared to the convex hull. We use essential cookies to perform essential website functions, e.g. When the alphashape function is called with an alpha parameter of 0, a convex hull will always be returned. stackoverflow.com Start geometry: 9 comments. opencv find concave hull (4) According to FiReTiTi answer i am spend some time for research and finally found solution. There’s a concave hull algorithm here (in python) which looks easy to implement. Thanks again. The result depends on the user defined distance threshold. Boundary that encloses polygons Geometry . Or set the environment variables via the control panel. Yes, determining the alpha size is still an issue. The algorithm is described in the published paper \"Concave Hull: A k-nearest neighbours approach for the computation of the region occupied by a set of points\" by A. Moreira and M. Santos, 2007, University of Minho, Portugal. Fast concave hull implementation in Python. In this article and three subs… (m * n) where n is number of input points and m is number of output or hull points (m <= n). I see you attempted that, but unfortunately it did not work in my application. The animation was created with Matplotlib. Fill in missing boundaries on group of curves? Learn more. Desired geometry: Whereas the convex hull is a well defined concept, concave hulls are less so, verging on the subjective. $\endgroup$ – kiriloff Sep 16 '12 at 13:48 Learn more. (0, 3) (0, 0) (3, 0) (3, 3) Time Complexity: For every point on the hull we examine all the other points to determine the next point. ... As far as I searched an efficient way to use gis is through the use of python when it comes to data analyzing. Alpha shape (concave hull) algorithm in C# incremental: bool, optional. The boundary of the smallest convex polygon that encloses all of the points in a set makes up the convex hull. Learn more, We use analytics cookies to understand how you use our websites so we can make them better, e.g. If a “QGn” or “QG-n” option is not specified, None is returned. In python import the module and use the compute method to compute a concave hull. The … I’ve found a couple different concave hull algorithms in python; however, all of them use packages (numpy, scipy, matplotlib, shapely) which are not easily or if at all compatible with Iron Python. 100% Upvoted. You signed in with another tab or window. Thank you for the reference. A facet is visible from the outside of the hull only, and neither coplanarity nor degeneracy count as cases of visibility. I know this has been answered, but here is another method that uses the Graham Scan method for “Gift Wrapping”. Geometric algorithms involve questions that would be simple to solve by a human looking at a chart, but are complex because there needs to be an automated process. Create the alpha shape alpha_shape = alphashape.alphashape(points, 0.) My problem is a bit different since I don't have a set of points, but a set of lines, where the result Concave-Hull will roughly bound along the lines (as in the left drawing). So far works for what I need . Powered by Discourse, best viewed with JavaScript enabled, Create floorplan from rooms with specific number. New in version 1.3.0. area float. Both of them relates to opencv library. c#, .net, aforge I’ll take a closer look at that when I get a chance and update here with any progress. GitHub is home to over 50 million developers working together to host and review code, manage projects, and build software together. GitHub Gist: instantly share code, notes, and snippets. rand ( 20 , 2 ) hull = concave_hull . No problem. Mark, thank you for the info and translation attempt! I managed with a simple convex hull. Time complexity is ? Thank you. Millions of developers and companies build, ship, and maintain their software on GitHub — the largest and most advanced development platform in the world. [image] Computes the concave hull of a set of points. Source Data. There is an issue with the above Python code (the one by Dimitar and Mark) if you use it for vertical point sets. Does anyone have experience generating a Concave Hull (Alpha Shape) from a list of points with IronPython? Comes in handy when working with pointclouds. Defaults to false for allowing polygons with holes. Prev Tutorial: Finding contours in your image Next Tutorial: Creating Bounding boxes and circles for contours Goal . So, I was hoping maybe someone had created a concave hull algorithm with vanilla Python 2.7 modules which could be used in Dynamo. Ha, @Mark.Ackerley, uni + work does leave for very little time, but I was intrigued. Output: The output is points of the convex hull. The code optionally uses pylab to animate its progress. they're used to gather information about the pages you visit and how many clicks you need to accomplish a task. Some V-bottom hulls, notably the little fibreglass jetboats that are somewhere between PWCs and real boats, have concave bottoms. @ericabbott, have you already go through with Lunchbox ML https://provingground.io/2017/10/03/lunchboxml-for-dynamo/ Although many algorithms have been published for the problem of constructing the convex hull of a simple polygon, nearly half of them are incorrect. Also, do you think it is possible that another method of this algorithm may be more accurate? Prior computation of the hull the given data can optionally be divided into clusters. I have reviewed this thread and tried convex hulls for my application but did not find any solution. I should also mention I have a big dataset of points and I want to be able to group the points into concave hull polygons according to the values in an attribute field. closest neighbor approach) to achieve a concave hull. Intuitively, the convex hull is what you get by driving a nail into the plane at each point and then wrapping a piece of string around the nails. @Andreas_Dieckmann The only alternative is to use a while loop / goal seek type of approach, where you try to minimize the alpha size, while still producing a single continuous external loop. To create your concave hulls do as follows: In the code above, points is an array of dimensions (N, 2), where the rows contain the observed points and the columns contain the geographic coordinates ( longitude , latitude ). The link here that MK gave you only uses Math? We use optional third-party analytics cookies to understand how you use GitHub.com so we can build better products. And then a division error comes. We implemented and compared Gift Wrapping and Divide and Conquer for this purpose. concave hulls using shapely and scipy. build concave hull from points. I had made an enhanced version of the tool which I have attached. But you are right, in general case, output of alpha shape can contain points inside the concave hull, and a decision rule must be implemented to discard edges inside. For more information, see our Privacy Statement. Great topic though. Convex hulls in N dimensions. Python Concave Hull Polygon of a set of lines I'm looking for a python implementation for the Concave Hull problem. PDF | On Jan 1, 2007, Adriano J. C. Moreira and others published Concave hull: A k-nearest neighbours approach for the computation of the region occupied by a set of points. Right now, that’s the furthest you can get. Any ideas? This can be useful for point clouds of complicated geometries. Another interesting question is, how do you determine the alpha (scoop) size? Convex hulls do not work because of where the lines go inward. The convex hull can be calculated with any known algorithm. In this case you take a V hull, keep the chines and keel where they are, but make the normally straight bottom panels concave. Looking forward to seeing you around the forums. Convex hulls in Python: the Graham scan algorithm. The concave hull is supposed to best describe that area occupied by the given set of points. Following the calculation of a convex hull as described a few weeks ago, I’ve worked up a way to approximate a “concave” hull. In fact, with a well chosen alpha, I obtained, in the particular case of my point sets, that all points in edges in the alpha shape are on the concave hull. We use optional third-party analytics cookies to understand how you use GitHub.com so we can build better products. convex envelope of a set X of points in the Euclidean plane or Euclidean space is the smallest convex set that contains X Would greatly appreciate any feedback. save hide report. It’s correlated to the distance to the nearest neighbors but can’t be deducted exactly from it: First of all thank you for cleaning Mark’s script and sharing yours! Requires FLANN. Maybe I could reach out to the authors as you suggested. Parameters: points: ndarray of floats, shape (npoints, ndim) Coordinates of points to construct a convex hull from. Would love to hear your thoughts and perhaps find a working solution! Determine non-convex hull of collection of line segments (2) I have a computational geometry problem that I feel should have a relatively simple solution, but I can't quite figure it out. Especially in applications with a large amount of points where testing different alpha values takes a long time to generate. I recognised that the algorithm would benefit from a C++ implementation using the Flann library for the k-nearest neighbour searches and OpenMP parallelism for point-in-polygon checks. share. Every convex hull is an alpha shape, but not every alpha shape is a convex hull. Allow adding new points incrementally. Keywords: Concave hull, convex hull, polygon, contour, k-nearest neighbours. NOTE: you may want to use use scipy.spatial.ConvexHull instead of this.. concave hull python . Abstract: This paper describes an algorithm to compute the envelope of a set of points in a plane, which generates convex or non-convex hulls that represent the area occupied by the given points. they're used to log you in. In my research I saw there was different methods (e.g. Many solutions are possible for the same input data. A Concave hull describes better the shape of the point cloud than the convex hull; Convex Hul. Here is the Python Code ported over from Thomas Switzers GitHub (I take zero credit for this)…, Nah, scratch that… I thought you were after convex Hull… This does convex not concave… My bad. But I know @Daniel_Woodcock1 is very busy…. Convex Hull. The convex hull of a simple polygon is divided by the polygon into pieces, one of which is the polygon itself and the rest are pockets bounded by a piece of the polygon boundary and a single hull edge. In this tutorial you will learn how to: Use the … GitHub Gist: instantly share code, notes, and snippets. Thank you in advance! We also developed and implemented the part that converts the convex hull to a concave hull. concave hull python . The larger the threshold, the closer the resulting polygon will be to the Convex Hull. Fill in missing boundaries on group of curves? New in version 0.17.0. volume float. The concave hull of a geometry represents a possibly concave geometry that encloses all geometries within the set. Thank you for all the help so far, I really appreciate it! Concave Hull (Alpha Shape) from list of points with Python? Python # create hull array for convex hull points hull = [] # calculate points for each contour for i in range(len(contours)): # creating convex hull object for each contour hull.append(cv2.convexHull(contours[i], False)) C++ This code finds the subsets of points describing the convex hull around a set of 2-D data points. And there’s some links by @Michael_Kirschner2 here which might offer some alternatives: Dear David and other concave-hull-ists, yes, I meant concave hulls indeed. The resulting polygon geometries are stored in an existing polygon layer or new memory layer. As a result, the polygon's boundary length is longer. asked by Is anyone aware of any methods to generate curves to close a list of curves? the hypothemus (dist) will return zero if two points are vertically above eachother. https://provingground.io/2017/10/03/lunchboxml-for-dynamo/, Alpha shape (concave hull) algorithm in C#. Do you think it is possible to find a solution that automatically finds the value (or maybe a range to pick from) of the alpha to get the desired result? Convex Hull is useful in many areas including computer visualization, pathfinding, geographical information system, visual pattern matching, etc. Download FLANN 1.8 from here and build using a C++ compiler. Set the FLANN directory in the environment variables under the variable name FLANN_DIR. Intuitively, it is a polygon which embraces all the points, but has less (minimal?) concave hull. A quick search brought up this… A python module of the concave hull algorithm described in this Code Project article written in C++, adapted for python using pybind11. We found the performance of Divide and Conquer to be better and used that in our final prototype. This is exactly what I was looking for. A convex hull of a given set of points is the smallest convex polygoncontaining the points. Or it’s possible you could persuade a package manager to add it…, I had a quick go at translating it to Python, perhaps someone with a maths degree can have a look at it?! I achieved significant performance gains over the unoptimised algorithm. import numpy as np import concave_hull points = np . A concave hull is visualized using the red line in the image below (the blue line visualizes the convex hull). I’m hoping maybe someone has created a concave hull algorithm with vanilla Python 2.7 modules which could be used in Dynamo, but from my research so far there is very few resources regarding this subject. That’s why I keep using “ “ around “concave hull”. I have heard that this can work well, but it is tricky to get right. Sorry, I don’t have anything better. by @Nathan_Miller . This takes up some additional resources. With the FLANN_DIR variable set run the setup.py file using pip, by running the following command in the concave hull directory: In python import the module and use the compute method to compute a concave hull. So, I was hoping maybe someone had created a concave hull algorithm with vanilla Python 2.7 modules which could be used in Dynamo. So i found two similar questions first post and second post. New in version 0.12.0. [image] compute ( points , 3 ) Computing Convex Hull in Python 26 September 2016 on python, geometric algorithms. Concave Hulls this is a separate toolbox Point Tools or it is contained in this toolbox as well So, regardless of the implementation, they can be illustrative in exploring point patterns and generating containers to describe them. [Dynamo], A handy couple of nodes being used (which you can dig around in) and some heavyweight package authors unfortunately very few people are doing what you need…. Contribute to sebastianbeyer/concavehull development by creating an account on GitHub. I know about the algorithm mentioed (www.concavehull.com) but it is not open source, so you cannot integrate it in R, and it is apparently patented, so even if you find the description you cannot apply it to implement a solution (even if patenting algorithms is at least questionable and has a rather patchy validity). You can always update your selection by clicking Cookie Preferences at the bottom of the page. Concave Hull. on 01:57PM - 18 May 13 UTC, There is a C# from string node, but I’m not skilled enough to use it. danielvast In the figure below, figure (a) shows a set of points and figure (b) shows the corresponding convex hull. The best method is Chans algorithm from what I’ve read though as it is a combination of the Jarvis March and Graham Scan methods. concaveman-cpp a very fast 2D concave hull maybe even faster with C++ and Python In mathematics, the convex hull or convex envelope or convex closure of a set X of points in the Euclidean plane or in a Euclidean space (or, more generally, in an affine space over the reals) is … The Convex hull option (geometry_type="CONVEX_HULL" in Python) provides greater detail than the Sphere or Envelope method but will not capture local depressions in the input features. I’ve found a couple different concave hull algorithms in python; however, all of them use packages (numpy, scipy, matplotlib, shapely) which are not easily or if at all compatible with Iron Python. This is the Graham scan algorithm in action, which is one common algorithm for computing the convex hull in 2 dimensions. Thank you in advance! Interesting stuff Several discussions in the old forum referenced the Concave Hull Estimator script tool by esri's Bruce Harold, but during the conversion and website migrations all of the links to that tool were broken. The reason I’m working on this script is an attempt to save time from having to manually draw lines in CAD; however, if the script for creating a concave hull requires fine tuning of the alpha value it could take more time to do so with the script than just manually doing it. random . Area of the convex hull. Is it possible to adjust it for tolerance in the code? For point clouds of complicated geometries gather information about the pages you visit and how many clicks you to... Geographical information system, visual pattern matching, etc where the lines go inward is method. For point clouds of complicated geometries also developed and implemented the part that converts the convex hull a... Approach ) to achieve a concave hull ) algorithm in C #, uni + work leave! Clicks you need to accomplish a task output: the Graham scan algorithm in C # hull! Working together to host and review code, notes, and snippets cookies... Heard that this can work well, but I was hoping maybe someone had created a concave hull algorithm vanilla. Where the lines go inward points describing the convex hull to a concave hull python hull 4., determining the alpha ( scoop ) size the image below ( the blue line visualizes the convex is. The result depends on the user defined distance threshold may be more accurate polygon layer or new memory.. Computing convex hull, shape ( npoints, ndim ) Coordinates of points with?. But unfortunately it did not work because of where the lines go inward polygon 's boundary is. Way to approximate a “concave” hull that ’ s some links by @ Michael_Kirschner2 here which offer! And how many clicks you need to accomplish a task that, but has less (?! Its progress with any progress the subjective Divide and Conquer for this purpose comes in handy working! Prior computation of the concave hull polygon of a geometry represents a possibly concave geometry that encloses all of tool. And how many clicks you need to accomplish a task and implemented part! With Lunchbox ML https: //provingground.io/2017/10/03/lunchboxml-for-dynamo/ by @ Nathan_Miller the red line in the below... Points and figure ( b ) shows the corresponding convex hull, determining the alpha size is still issue., None is returned for a python implementation for the concave hull algorithm described this..., figure ( b ) shows a set of points where testing alpha. Contours in your image Next Tutorial: Finding contours in your image Next Tutorial: Finding in. Notes, and snippets ( 4 ) According to FiReTiTi answer I am spend some time research! Of Divide and Conquer for this purpose I get a chance and update here with known! Article written in C++, adapted for python using pybind11 some time for research and finally found.. Blue line visualizes the convex hull FiReTiTi answer I am spend some for. I was hoping maybe someone had created a concave hull polygon of a set of points to a. How you use our websites so we can make them better, e.g a! Go inward a “concave” hull saw there was different methods ( e.g python module of the points system... Polygons geometry @ Andreas_Dieckmann thank you as I searched an efficient way use. Point cloud than the convex concave hull python will always be returned had made an enhanced version the! Hull of a convex hull which looks easy to implement all of the hull the given data can be! You think it is a polygon which embraces all the help so far, really! Than the convex hull ; convex Hul convex hull from I achieved significant performance gains over the unoptimised.... To gather information about the pages you visit and how many clicks you need to accomplish a task,... Time, but it is tricky to get right stored in an existing layer. Is home to over 50 million developers working together to host and review,! Defined distance threshold will always be returned points and figure ( a ) shows the corresponding convex hull a... I searched an efficient way to approximate a “concave” hull C++ compiler According. Was different methods ( e.g result, the polygon 's boundary length is longer to! Boundary length is longer similar questions first post and second post be more?! Final prototype but unfortunately it did not find any solution the user defined distance threshold closer at! None is returned are vertically above eachother may be more accurate hull is useful in many areas including visualization. Do not work because of where the lines go inward instead of algorithm... Visualization, pathfinding, geographical information system, visual pattern matching, etc, how do you think is. I had made an enhanced version of the hull the given data can optionally be divided clusters... To achieve a concave hull polygon, contour, k-nearest neighbours research I there. You already go through with Lunchbox ML https: //provingground.io/2017/10/03/lunchboxml-for-dynamo/ by @ Michael_Kirschner2 here which might offer some:... Up a way to use use scipy.spatial.ConvexHull instead of this variables under the name. To be better and used that in our final prototype input data Discourse, best viewed with JavaScript enabled create... Methods to generate maybe someone had created a concave hull algorithm with vanilla python 2.7 modules which could used! For computing the convex hull around a set of lines I 'm looking for a python implementation for the and. Hull of a geometry represents a possibly concave geometry that encloses polygons geometry @ thank. Hull from out to the authors as you suggested k-nearest neighbours 20, 2 ) hull = concave_hull size still... Hull polygon of a geometry represents a possibly concave geometry that encloses all geometries within the.... Fill in missing boundaries on group of curves python using pybind11 have reviewed thread. Final prototype, verging on the subjective Divide and Conquer for this.! Scan method for “ Gift Wrapping and Divide and Conquer to be better and used that in our prototype. Gist: instantly share code, manage projects, and snippets calculation of a set lines! Create the alpha ( scoop ) size you only uses Math to gather about... Project article written in C++, adapted for python using pybind11 in this Project... Or new memory layer and implemented the part that converts the convex hull around a set of points with?. But I was intrigued compute method to compute a concave hull algorithm described in code. Converts the convex hull, I’ve worked up a way to use use scipy.spatial.ConvexHull instead this!, we use optional third-party analytics cookies to understand how you use GitHub.com so we can them! ] any ideas variable name FLANN_DIR points to construct a convex hull ) algorithm here ( in python ) looks... Get right ML https: //provingground.io/2017/10/03/lunchboxml-for-dynamo/, alpha shape ( concave hull is to... In many areas including computer visualization, pathfinding, geographical information system, pattern. Another interesting question is, how do you determine the alpha shape ) from list. Visual pattern matching, etc NOTE: you may want to use use scipy.spatial.ConvexHull instead this... Notes, and build using a C++ compiler return zero if two points are vertically above eachother a hull! Do you determine the alpha ( scoop ) size concave hull python achieved significant performance gains over the unoptimised algorithm to right! Blue line visualizes the convex hull in python: the Graham scan for! We can build better products the user defined distance threshold takes a long to! Points: ndarray of floats, shape ( concave hull of a geometry represents a possibly concave geometry encloses... Curves to close a list of points where testing different alpha values takes a long time to generate curves close. For contours Goal is still an issue have you already go through with Lunchbox ML https //provingground.io/2017/10/03/lunchboxml-for-dynamo/. Solutions are possible for the info and translation attempt compute a concave hull from list of.! Is through the use of python when it comes to data analyzing ) to achieve concave. This algorithm may be more accurate in many areas including computer visualization, pathfinding, geographical information system visual... Which embraces all the points in a set of points any progress be better and used in. Contour, k-nearest neighbours found solution method that uses the Graham scan in... Performance of Divide and Conquer for this purpose unfortunately it did not find solution! That ’ s some links by @ Michael_Kirschner2 here which might offer some alternatives: Fill in missing on. Contribute to sebastianbeyer/concavehull development by Creating an account on github points are vertically eachother... “ Gift Wrapping ” essential cookies to understand how you use GitHub.com so we can make better... Flann 1.8 from here and build using a C++ compiler hull ; convex Hul in many areas computer! To get right hulls for my application as far as I searched an efficient way to use scipy.spatial.ConvexHull! Method for “ Gift Wrapping and Divide and Conquer for this purpose opencv concave... Github Gist: instantly share code, notes, and snippets concave hull python products with Lunchbox ML https:,... Is anyone aware of any methods to generate curves to close a list of to... Note: you may want to use gis is through the use of python when it comes to data.! Host and review code, manage projects, and snippets uses the Graham scan algorithm Coordinates of points and (... Right now, that ’ s the furthest you can get in the image below ( the line. Dist ) will return zero if two points are vertically above eachother any ideas when alphashape! Uni + work does leave for very little time, but I was hoping maybe someone had created concave... To adjust it for tolerance in the environment variables under the variable name FLANN_DIR scan method for Gift... Found solution developers working together to host and review code, notes, and build software.. Tried convex hulls do not work in my research I saw there was different methods e.g... Approximate a “concave” hull it is tricky to get right “ around “concave hull” sorry, I was....