Dear friends, Do you know how to calculate the CONCAVE hull of a set of points (2- dimensional or n-dimensional)? Success! 11 $\begingroup$ I have a list of discrete points wich I want to use as nodes for creating a 2D mesh. MeshCollider.convex. This shape is called a convex hull, and there are several algorithms you can use to find this convex hull. This defines a concave volume. For α = π, this problem converts to MAP as it is proved to be NP-complete. Here is a github repo on finding the concave hull for a set of points using python.. My recommendation to you is the following. CreateConvexHull(SetOfPoints) pointOnHull = leftmost point in SetOfPoints i = 0 repeat P[i] = pointOnHull endpoint = SetOfPoints[0] // initial endpoint for a candidate edge on the hull for j from 1 to |SetOfPoints| if (endpoint == pointOnHull) or (SetOfPoints[j] is on left of line from P[i] to endpoint) endpoint = SetOfPoints[j] // found greater left turn, update endpoint i = i+1 pointOnHull = endpoint until … Key words. The program has only two easy steps: Set a convex hull from a set of points (In the program they are the Node objects). The 2D case is discussed in some detail here. 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. The larger the threshold, the closer the resulting polygon will be to the Convex Hull. With Unity5 I have to flag the collider as "Convex" in order to select "Is Trigger"... the problem is that now I get an error: Cooking::cookConvexMesh: user-provided hull must have less than 256 vertices! And with just one click! To recap: the idea of the area trigger concept is that it exists of a height and a 2d polygon, that can be concave. In kinda sorta quasi-pseudocode. Given: n points that are strongly correlated to a 3d k-sided non-convex polygon, where n >> k, Find: the best fit concave-hull that matches the original geometry of the points. and it doesn't work anymore. In Unity 2017.3 and later you can mark the convex mesh to be inflated from the “Cooking Options” dropdown making sure “Inflate Convex Mesh” is enabled. How it works. The Voronoi regions of the points on the boundary will tend to be either infinite or much longer than the ones on the interior. The α-concave hull on a set of points in the plane is a non-convex hull with angular constraints under the minimum area condition. Hi all, I've been working on a project that needs detailed raycasting collisions for ballistics hit calculations. DelaunayMesh in a specified closed region - creating a concave hull from a set of points. I guess it was a bit poorly worded, I'll edit it now. We are here going to use the Gift wrapping algorithm, also known as a Jarvis March. 5 Thanks in advance, If your concave corners are not too sharp, I might try doing a 3d Delaunay triangulation on the point set. Here I am using the exact same technique as used before, and here is what it looks like: To run it, you first need to transform your cloud of 3D points into a volumetric dataset. Input would be simply a high density point cloud that is approximately uniformly distributed random points within the polygon plane, with a bit of noise. Step 1 is to sort all vertices to figure out which one has the smallest x coordinate, and if there are multiple points with the smallest x coordinate, we pick the point with the smallest x and z coordinate. A convex hull of a set of points is the uniquely defined shape that minimizes the area that contain all the points, without having any angle that exceed 180 degrees between two neighbouring edges, as seen in Figure 2.1a. In 2D, I implemented a Python concave hull algo using this representation: half-edge data structure. Active 4 years, 6 months ago. In 2D, I implemented a Python concave hull algo using this representation: half-edge data structure. I used DelaunayMesh and it works fine. You can find them here: Convex hull algorithms. There's always tradeoffs. Then the lower and upper tangents are named as 1 and 2 respectively, as shown in the figure. (max 2 MiB). Thank you for helping us improve the quality of Unity Documentation. Output would be the vertices of the polygon in 3d points. Also, rasterization of the points into 2d and then preforming a edge find is pretty costly. For α = 0, computing α-concave hull is equivalent to that of computing convex hull with O (n log ⁡ n) optimal algorithm. In older versions of Unity there’s simply a tickbox to “Inflate Mesh” on mesh colliders. The result depends on the user defined distance threshold. Faster algorithms tend to be more complicated if you have colinear points, while the Jarvis March algorithm will be able to deal with colinear points and other numerical difficulties without any problems. This point is always on the convex hull. Leave feedback. We found out that the convex decomposition algorithm is quite sensible to the scale of the mesh. The code in that post is obsolete in Unity 5 (as are many of my other Unity-related posts). In some cases yes. Convex Hull: Concave Hull: Many solutions are possible for the same input data. Let the left convex hull be a and the right convex hull be b. Suggest a change. It comes with a simple demo for the Unity game engine using just gizmos. Andrew's monotone chain convex hull algorithm constructs the convex hull of a set of 2-dimensional points in (⁡) time.. It should look like this in Unity if you have 200 random points: 2. I'm looking for a C# implementation of the Concave hull (alpha shapes) algorithm. To know if two points are on the convex hull, we have to check all other points and make sure none of them are to the right of a line between the two points. Here is an example using Python. C#; Scripting API. What if you have several random points and want to find the smallest shape that's enclosing these points. 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. Concave Hull Generator Standard Triplanar Toon Standard Toony Standard Standardize Bows Standard Assets Example. Language English. 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. It does so by first sorting the points lexicographically (first by x-coordinate, and in case of a tie, by y-coordinate), and then constructing upper and lower hulls of the points in () time.. An upper hull is the part of the convex hull, which is visible from the above. But in some cases this algorthm is fast if not all points are on the convex hull. It sounds like you want to compute the concave hull of a collection of points in 3-space projected onto a plane. So I've updated the code on bitbucket. To find a "concave hull" around a set of 3D points, I found that using the marching cube algorithm for volumetric data works best. Following your suggestion, I did the following: Obtained the (lat, lon) hull values using from shapely.geometry import LineString and then, with the boundary values in hand, I projected them to the Earths surface using Pyproj and finally estimated the area using from shapely.geometry import shape.I can provide a code snippet if any of you want it. First of all you are to choose a representation for your mesh. Convex Hull: A 'convex hull' is as if you wrapped the object in paper, all the holes and concave parts will not be represented, just the outer most features (see the teapot example below). The AR-Toolkit is a Unity toolkit created by Stefan Volkers to create Augmented Reality Projection Games. If you still wan… Project the points onto a plane (This is pretty much what you have been doing) then compute the 2d Delaunay triangulation to find the edge points and continue as above. The other implementation are quite complicated and will take a lot of time to convert so I'm looking for a C# version which is already working. To find the convex hull of a set of points is a well-known problem studied in detail and there are many existing algorithms. unity.com; Version: 2019.4. If you are confused, you should look at this YouTube video. And I do mean polygon, because I am looking for a 2-D shape projected into 3-D, https://stackoverflow.com/questions/3444001/simplified-concave-hulls/3453790#3453790, https://stackoverflow.com/questions/3444001/simplified-concave-hulls/3445440#3445440, It seems that the 2D case you linked to is more of the sparse point variety. The solution is to add some padding to these skinny clusters. One question that gets raised relatively frequently over at the MSDN Spatial forums is how to create a concave hull around a set of points. Any pointers would be great. My question is, is there a better way to approach this problem? Then, algorithm in 2D (you should adapt to 3D) can be close to alpha shape algorithm, by Edelbrunner. (With a "smoothing" parameter of course). Click here to upload your image How do you know if you have passed a waypoint? I achieved significant performance gains over the unoptimised algorithm. The above approach works, but it is probably best to do it in two steps. Unite all dots under the smallest possible area. You also need an algorithm to figure out if a point is to the left, to the right, or on the same line as 2 other points. This parameter forces the convex decomposition computation to be done using the mesh rescaled to fit a sphere with radius = Internal Scale. Ask Question Asked 5 years, 2 months ago. A Concave hull describes better the shape of the point cloud than the convex hull. Language English. A hull that's very easy to propel … Check out my 3000 subs Special Video: https://youtu.be/Xm84wdUOE4MThanks for watching! Similary, cells on the boundary that are associated with a single face of the polyhedron will tend to be aligned in a direction nearly normal to the face that they are associated with, in that they will all be long and thin and their long axes will be nearly parallel and pointing out of the polygon. First find the plane in which the polygon lies, doing a least squares fit of a small sample of the points is probably good enough. Turn left or right to reach a waypoint? To demonstrate how the proposed concave hull generating procedure works, a case study has been performed, and using the information of the concave hull generated, a physical model of the fractal has been produced with the aid of additive manufacturing (3D printer). Concave hull generator. So the algortihm is sometimes slow, but robust. Loop to generate the convex hull Vertex currentPoint = convexHull[0]; //Store colinear points here - better to create this list once than each loop List colinearPoints = new List(); int counter = 0; while (true) { //After 2 iterations we have to add the start position again so we can terminate the algorithm //Cant use convexhull.count because of colinear points, so we need a counter if (counter == 2) { … We can then add a mesh trigger and flag it as convex. The Concave Collider helps overcoming this limitation by providing a way to automatically compute a set of colliders that can fit any shape; convex or not. Then use the linked to code to generate a concave hull for these points, with some guess for the value of alpha. Perhaps you need to define 'best'. By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy, 2020 Stack Exchange, Inc. user contributions under cc by-sa. Dear dwyerk. Share. Then, algorithm in 2D (you should adapt to 3D) can be close to alpha shape algorithm, by Edelbrunner. The problem with the above solution is that the points can be noisy. By using our site, you acknowledge that you have read and understand our Cookie Policy, Privacy Policy, and our Terms of Service. Show all projects by intrepion. 4. ...and follow me on Twitter: @eriknordeus. The coordinate where a ray intersects with a plane, algorithm to figure out if a point is to the left, to the right, or on the same line as 2 other points. Version: 2019.4. First of all you are to choose a representation for your mesh. Create a set of points using the endpoints of each line. In this case you take a V hull, keep the chines and keel where they are, but make the normally straight bottom panels concave. It is very important that they all have an unique id value. Collision detection algorithms for something you know is convex is much faster than concave… Calculating the concave hull was really expensive, and since I could now distinguish multiple objects, the concave algorithm became a bit unnecessary. Step 2 is to loop through all other points to identify which points are on the convex hull. Also did you mean 3D k-sided polyhedron instead of polygon? 3. Playing with this value can improve the final results. I already found several Java, Python and C++ implementation but no C# version. You can also provide a link from the web. Then the red outline shows the final convex hull. Use Unity to build high-quality 3D and 2D games, deploy them across mobile, desktop, VR/AR, consoles or the Web, and connect with loyal and enthusiastic players and customers. To make all this work in Unity you need random points in x-z-space and they should be stored as a Vertex in a list (Create a new Vertex object with a Vector3 as its position and where y = 0). Example Project that comes with Unity 5. Viewed 2k times 19. More Unity Games & Projects. So I switched back to using the convex hull. The concave hull polygons generated by this algorithm still need some further processing, because they will only discriminate points inside of the hull, but not close to it. In my case, for a simple 9 sided concave polygon, there may be around 40000 points. I have heard that this can work well, but it is tricky to get right. Our concave collider component enables complex mesh to mesh collisions. Includes 5 different sample scenes. Now the problem remains, how to find the convex hull for the left and right half. Unity is the ultimate game development platform. Edit Now I see that you just want a polygon. In Unity, mesh to mesh collisions only work if at least one of the meshes is convex. If I used the same algorithm, it seems that it would be wildly inefficient, https://stackoverflow.com/questions/3444001/simplified-concave-hulls/16412653#16412653. 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