Questions tagged [computational-geometry]
The study of efficient algorithms and data structures to solve various problems involving point sets, line segments, polygons, polyhedra, simplices, etc.
0
votes
1answer
51 views
Ordering points from X Y coordinates
I have series of points extracted from a regular grid, with their X/Y coordinates. A previous algorithm (that I cannot modified!) output a list of these coordinates, but the ordering of these point is ...
-1
votes
0answers
30 views
Finding the Proportions of and Programatically Representing Topological Disks
I am currently in the process of writing an internal software package that will be used for computational geometry research. I am interested in being able to programatically generate isotoxal ...
2
votes
2answers
67 views
projective reconstruction from orthogonal views
This is a problem from projective geometry. Suppose I have a vector $z \in R^k$ of unit length $\| z \| =1$ inside a $k$-dimensional hypercube. I don't know its value but do know its projection upto ...
3
votes
1answer
65 views
Smoothness regularisation of a 2D field on a triangular mesh?
I'm working on an inverse problem where the solution is the values of a 2D scalar field at the vertices of a 2D triangular mesh, such that the field can be defined continuously inside the mesh via ...
2
votes
1answer
110 views
A robust algorithm to sort a non-convex polygon vertices
Let v_{0},...,v_{N-1} be N points in a Cartesian xy plane defining the vertices of closed polygon (i.e. v_{N} = v_{0}).
Let P_{0}...
1
vote
1answer
73 views
Node renumbering in a 2D mesh
I have a 2D domain which is discretized using Q4 elements. I have the nodal positions and the element connectivity matrix. I would now like to renumber the nodes in such a way that all the interior ...
1
vote
1answer
86 views
How to generate a face list from vertices?
I have a little background in writing toy finite volume CFD codes. In 2D Cartesian scenarios, I typically take $x_{\min}$, $x_{\max}$, $y_{\min}$, $y_{\max}$, and the number of points in $x$ and $y$ ...
2
votes
0answers
103 views
Efficient root finding algorithm for monotonic function
This is my first time asking a question here, so I may not be asking this in the right place. I am trying to find the roots of a monotonic function with as few function evaluations as possible.
I ...
3
votes
0answers
30 views
Minimum axis aliged bounding box of convex polytope
I need to compute a $n-$dimensional integral with $n<10$ on a convex polytope. Since most numerical integration libraries (e.g. Cuba) expect the function to be integrated defined inside an axis ...
1
vote
0answers
101 views
Smallest circumscribed circle in spherical geometry
I work in Python 3 on astrophysics projects. I need to compute the smallest circumscribed circle of a set of points in the sky (so described by Right Ascension and Declination). I have found a code ...
3
votes
0answers
47 views
Approximate the largest simplex in N-dimensional Delaunay triangulation
I am working on determining the spatial information of a set of $M$ points in $N$-dimensional space. It is well-known that the construction of Delaunay triangulation is expensive in high dimensional ...
1
vote
0answers
43 views
Uniformly sample a point per polytope
I want to uniformly sample a point within each of $10^5$ convex polytopes in each iteration of a solver.
The polytopes in one iteration are completely different from the polytopes in another iteration....
2
votes
0answers
76 views
How to numerically optimize affine transformations?
I need to optimize affine transformations for of a set of triangles using energy function based on the connectivity.
The energy of an edge $e_j$ between triangles $T_a, T_b$ is given by
$$
E_j = \...
-1
votes
1answer
85 views
Compute outward normal and surface area for 8 noded brick element in FEA
I have a cube which is divided into 8 small cubes by bisecting each edge, I am trying to find out the surface area of each of the faces and the corresponding outward normals for them. This operation ...
-1
votes
1answer
100 views
Connectivity matrix in Finite Element Method in Triangular elements
Imagine a simple triangular base mesh in finite element method with an unknown number of elements (varying by the user). How can connectivity matrix be coded to be generated automatically?
6
votes
1answer
222 views
Putting N hard spheres randomly in given volume
I need to put $N$ spheres with given radius $R$ randomly in a Volume $[-0.5,0.5]^3$, without any overlap of spheres.
If I choose values so that all the spheres will occupy ~57% of the total volume, I ...
1
vote
0answers
158 views
Use of Morton Key to reduce number of grid points
I asked a question on Stack Overflow Performance Issue with VP Trees and Nearest Neighborsand I was not satisfied with the answer and so I thought I would reword my question for this site and post ...
1
vote
2answers
160 views
Uniform dots distribution in a sphere
I'm trying to implement Barnes-Hut algorithm, with a binary tree. My initial conditions are a uniform mass distribution in a sphere with radius $R$. How can I create uniform dots distribution in a ...
2
votes
1answer
124 views
Can the Power Method be used here?
Given a set of $n$ points on which a triangulation is performed, it is possible to construct coefficients $\lambda_{ij}>0$ such that each point $x_i$ is a convex combination of the points connected ...
2
votes
0answers
67 views
Simultaneous update to barycenters
Suppose a tiling is given in 2D (an embedding of a planar triangulated graph), with all faces convex.
Now suppose one moves each point, one by one, to the barycenter of its neighbors. I think that ...
4
votes
0answers
78 views
What Derivative-free optimization method should I use when my initial guess is very good?
I am trying to minimize a function where my initial guess is quite close to the minimum.
I'm trying to minimize
$$f(q) = \text{angle}(qw_1q*, v_1) + \text{angle}(qw_2q*, v_2) + \text{angle}(qw_3q*, ...
4
votes
2answers
474 views
3D contour mesh computation
I have the value of a function in three dimensions, $f(x, y, z)$, which varies smoothly.
I would like to compute a 3D mesh where $f(x, y, z)$ has a particular value.
Are there algorithms to do this? ...
5
votes
1answer
152 views
Integrating/Implementing NURBS-related calculations
Recently, I started to develop some codes that use NURBS (general things I intend to use/already using: spline generation, interpolation, grids, isolines, closest-point find, and many others), both ...
2
votes
1answer
59 views
Polygon approximation with a circle
There is an article describing how to detect a pupil from an eye photo.
A.-H. Javadi, Z. Hakimi, M. Barati, V. Walsh, and L. Tcheang, "SET: a pupil detection method using sinusoidal approximation," ...
3
votes
0answers
74 views
Fast Algorithms for the Simplicial Decomposition of a Convex Polytope in N-Dimensions
I'm in the process of constructing an algorithm which computes the Voronoi diagram of a set of points, but I now need a method to decompose each Voronoi cell into simplices. The information we have is:...
1
vote
0answers
46 views
Efficient initial identification of solid or liquid domains for a block structured Cartesian grid generation system
INTRO
Within the last 5 days I was able to generate a block structured Cartesian grid
generation system with a combination of Fortran,C++ and Python.
I am running intersection tests of the ...
0
votes
1answer
110 views
Which free library should I use to perform cutting/clipping operation?
I have a set of points which forms a closed loop, and I want to perform cutting/clipping a 3D model using this loop. I have used VTK but in some cases, it has a "Cannot follow edges" problem.
Is ...
0
votes
1answer
58 views
Gmsh exporting wrong mesh DATA [closed]
so hopefully I'll be using gmsh to make meshes out of 2-D cross sections with o thickness. I tried to make a structured mesh with quad elements of a rectangular ...
4
votes
1answer
207 views
Expanding Winding Number algorithm to arcs
I have a problem that I have been attempting to solve for a few days now. I was wondering if I would be able to get some assistance from the community.
In order to detect if a point is in a polygon, ...
3
votes
1answer
135 views
Compute mesh of the projection of a 3D surface triangulation
Given a triangulated surface in $\Bbb{R}^3$ we can simply project it on a plane. This will result in a family of triangles which do not form a mesh of the projection for the following reasons:
each ...
7
votes
2answers
1k views
Efficiently finding all (x,y,z) points within certain distance of point P
I am using Python, and I have a Pandas dataframe with hundreds of thousands, if not millions, of $(x,y,z)$ coordinates. I am looking to find an efficient method to index the original dataframe so that ...
0
votes
1answer
53 views
Detect all “visible” points on a triangulated surface
I have a triangulated surface that I want to work with. In order to optimize certain quantities related to this surface I want to find all points which are accessible from a given direction. To be ...
2
votes
2answers
109 views
Algorithm to construct all distances of a system described by $3N-6$ distances
A non-linear molecule has $3N-6$ degrees of freedom ($N$ is the number of atoms; ignoring translation and rotation). Therefore, a set of $3N-6$ distances and/or angles is enough, to describe the whole ...
4
votes
1answer
120 views
Delaunay triangulation for datasets with four or more co-circular points
I am working on a library that requires subdivision of polygons into triangles. The polygons are divided into triangles by (more or less) random points that are inside them. In general, the approach ...
2
votes
2answers
112 views
Find connected circles
I have a problem as follows:
We have a set of circles (we know the radius r and the center point c in Rd of each circle)
We ...
7
votes
2answers
139 views
Generating set of points on a surface defined by constraint
I'm writing a differential geometry library, and one minor convenience I'd like to offer is to generate a set of points on a surface given by a constraint. For example, for a sphere,
$$x^2+y^2+z^2-r^...
0
votes
1answer
119 views
Linear Least-Squares Point-to-Plane ICP degenerative case
I'm trying to implement Linear Least-Squares Optimization for Point-to-Plane ICP Surface Registration
Paper describes linear approximation for point to plane distance for rigid ICP. This approach is ...
0
votes
3answers
67 views
Is it valid to assume the center of a bounding sphere to be also the center of the bounding box?
Computing an axis aligned bounding box of a point set is trivial. Computing a bounding sphere of a point set is also trivial when the center is known. Computing the center of the bounding sphere is ...
3
votes
4answers
343 views
find grid points inside the parallelogram defined by an origin and two vectors
I hope someone knows an efficient computational approach to the following 2D problem:
Given two vectors $\mathbf{A}$ and $\mathbf{B}$, find all grid points that lie within the parallelogram spanned ...
6
votes
4answers
1k views
Generate a set of orthogonal vectors to a given vector
I am looking for an alternative and robust alternative to Gram-Schmidt orthogonalization, but with one constraint:
I have a unit vector $\mathbf{v}_1 \in \mathbb{R}^d \,\text{s.t.} \,\|\mathbf{v}_1^T\...
1
vote
2answers
142 views
Sign of integer determinant 4 by 4
I'm in the context of this publication: http://www.gilbertbernstein.com/resources/booleans2009.pdf
I applied quantization to my point coordinates: All coordinates are integer lying in [0, 2 power 20]....
1
vote
1answer
61 views
Sources for verified Voronoi and power diagrams
In the course of trying to implement algorithms for Voronoi and Laguerre diagrams, I realized I needed to verify if my implementation is working correctly using a point (or circle) configuration with ...
0
votes
1answer
331 views
Algorithms to extract trajectory lines out of 3D point clouds
I am looking for different approaches to extract 3D polylines out of Point Clouds.
We are able to create these point clouds out of different data sources of real world surveys (LIDAR, RADAR, etc...) ...
0
votes
1answer
75 views
What is the expected value of area of intersection of a circle and a rectangle
$r$: cicle C1's radius
$w$,$h$: rectangle R1's edges: $x=w$, $y=h$, $x=0$, $y=0$
$(w>2r, h>2r)$
$S(x,y)$: area of ...
1
vote
0answers
35 views
Algorithms for computing winding numbers of 2-sphere maps
I have a question concerning computational geometry which arises in the simulation of fields with topological defects, and I'd like to know whether there's an efficient algorithm (or any algorithm) to ...
1
vote
1answer
62 views
Optimally “morph” one set of points into another
Given two sets of (two-dimensional) points, say, $A=\{a_1,a_2,\ldots,a_{n_a}\}$ and (you guessed it) $B=\{b_1,b_2,\ldots,b_{n_b}\}$, and $d^2_{i,j}=\mid a_i-b_j\mid^{\ 2}$ the "matrix" (not ...
0
votes
1answer
53 views
Efficient search strategy in a monotonic boolean function wherein the probability of solution location is known apriori
A boolean-valued monotonic function is defined in the set of positive integers, $\mathcal Z$.
$$f(n) = \begin{cases} 0, &n_{min}\le n < n\ast\\1, &n\ast\le n\le n_{max} \end{cases} ; n \in ...
1
vote
1answer
67 views
Distirbution of Points along a Line
I am facing the following problem:
Given is a line of length $L$ which I want to split into $N$ segments. The lengths of the first $(s_1)$ and last segment $(s_N)$ are given.
You can assume that the ...
1
vote
0answers
25 views
Use custom defined metric(not matrix) in Javaplex
I'm about to get started trying to use Javaplex for the first time for some application in topological data analysis (TDA) and I want to use a custom defined metric. From looking over the documents, I ...
0
votes
1answer
109 views
From edge-vertex connectivty to face-vertex connectivity?
I am working on mesh generation and optimization and encountered this problem. For example, in the figure below, we have the edge-vertex connectivity:
0-1
1-4
4-5
2-5
3-2
0-3
1-2
1-6
7-6
4-7
...
