Questions tagged [geometry]
The geometry tag has no usage guidance.
143
questions
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Which geometry file format is the most similar to our geometry file format?
To represent a 3D geometry in our software we use this format below:
Material-1 Material-2 P1(X1,Y1,Z1) P2(X2,Y2,Z2) P3(X3,Y3,Z3)
This 11 point gives us a triangle with the description of what is ...
1
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1answer
57 views
Help understanding tangent from dot product and max distance from component wise vector multiplication
I am looking through this code and seeing two things which confuse me (well, the whole functions does) in the top functions.
First, dir * p where ...
0
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0answers
44 views
Methods to interpolate between 2 topologically identical 3D meshes
I have 2 3D surface meshes. These meshes have vertex-correspondence and have the same topology (same edges and triangles connecting the vertices). However, the vertex positions (3d coordinates) are ...
4
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1answer
218 views
What are 'mesh clusters' / hierarchical cluster culling (with LOD?) / triangle cluster culling and how do they relate?
I've seen several references to this and related concepts now but I can't find any hard details about these systems, and how they are implemented.
The earliest reference I can find is from the "...
1
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1answer
53 views
Area-light approximation in 2D
I’m trying to render a 2D image something like this:
…where an arbitrary shape has its border illuminated by a line in a relatively physically accurate way, i.e. with less illumination reaching the ...
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0answers
24 views
Convert point clouds into voxels
I have points that are obtained by sampling a mesh(which is not watertight). Now, I would like to convert that mesh into voxel?
Does anyone have any suggestions for solving this problem?
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36 views
Bottom up (as opposed to top down) text on projective geometric algebra?
I have been reading the SIGGRAPH course notes on projective geometric Algebra, and I get some of what's going on. However a lot of the knowledge needed to understand these PGA notes seems to be based ...
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1answer
37 views
Computing heat diffusion creates weird results
I am trying to model heat diffusion on the surface of a mesh. I annexed the most important bits of theory about this topic as screenshots on the question see the bottom.
The crux of the issue is we ...
1
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1answer
52 views
getting the outline of an arbitrary set of shape unions
I hope this is the right forum to ask this question.
I want to experiment with procedurally generating some buildings, and as a first step I want to generate a 2D shape to use as a foundation for the ...
2
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0answers
42 views
Divide mesh according to level of detail
Background
I need to remesh by OpenVDB, like what Blender remesh does:
Voxel
Uses an OpenVDB to generate a new manifold mesh from the current geometry while trying to preserve the mesh’s original ...
5
votes
1answer
83 views
Existing method to automatically fill in this sort of concavity in meshes?
I am working with a PWP3D-like algorithm that renders silhouettes of a mesh in order to segment a frame of video and update an object's pose. Because it is only the silhouettes of the mesh that matter,...
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41 views
Under what conditions does a mesh operation cause the mesh become non-manifold and how to avoid it?
I'm implementing some mesh operations (e.g. edge collapse, edge split, edge flip etc) and need to ensure applying such operations does not cause the mesh to become non-manifold. However, I'm not sure ...
0
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1answer
76 views
Spline interpolation library in cpp
Have been searching a lot for a good spline interpolation library in cpp, came across one, which is the famous Eigen library , having the unsupported counterpart for spline fitting.<Here>.
I ...
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1answer
30 views
Differential or intersection of islands of 2D polygons in different layers
I have a 2D layer/section containing the 2D polygons colored in shades of green.
I have another layer containing the 2D polygons colored in shades of blue.
I intend to figure out how different are ...
0
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1answer
28 views
Render Duplicate Miniature Scene Replica
Context
I am working on project for implementing and user test a World-in-Miniature (WIM) interface for VR. A WIM essentially is a replica of the scene the user is currently in, but in miniature.
...
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37 views
Changing Coordinate Frames with Affine Transformations
Stuck with this questions could I get some help.
where uA and vA are two orthonormal vectors indicating the two axes, and oA is the origin. Suppose that all three frames of reference shown in ...
0
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1answer
33 views
Moving a vertex through the cursor
There is a way to move a selected point in a mesh with a cursor(assuming a camera that doesn;t change between frames).
The way I remember the algorithm (but seems to be wrong) is:
Unproject the ...
2
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0answers
76 views
How to compute a bounding tetrahedron
I'm wondering how to compute a bounding tetrahedron from a set of points so i can initialize a delaunay triangulation
My first approach was to find the bounding box to my set of points and then ...
1
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1answer
35 views
Subdivision scheme where the faces and edges have weights (not necessarily scalar weights)
Subdivision schemes work by considering the vertices and their connectivity information to calculate averaging weights.
However, other than specifying which vertices are connected, and perhaps which ...
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0answers
45 views
Algorithm to select regions based on curvature on a mesh
I'm trying to understand how to implement an algorithm similar to the one used by Magics' mark surface tool, you can see such behaviour on this video.
Quoting the video: "Basically with this tool ...
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2answers
130 views
Is there a tool capable of drawing a triangular linear gradient fill?
I need to draw some shapes filled with linear gradients starting from every point and blending smoothly between points, like an OpenGL standard shading (I guess it is called ...
0
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1answer
326 views
Vertices, Vertex Normals and Face Normals
Using Open 3D Model Viewer, I have converted an OBJ file to an STL file.
In the source file, the Vertex Normals are specified and in the destination, the face normal of the triangles are present which ...
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2answers
90 views
Rounding a 3D corner with Subdivisions
Following the instructions from this post on Stack Overflow, I have been able to find points A, B, and C from points V1, V2, and V3 and a radius value (code below). I would like to be able to find a ...
0
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1answer
35 views
In place sorting of a half edge DS?
Cross posting from SO because I didn;t know where to put this question.
I have an implementation of the half edge and I am trying to sort the edges such that edge n+1 is the pair of edge n.
Setup
I ...
3
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1answer
67 views
Why is the valence of regular vertices 6?
So I recently learnt that supposedly for any mesh, and pretty much any scheme, the valence of regular vertices must be 6. It seems to be related to the Euler-Poincare formula but I have not been able ...
2
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1answer
56 views
Sort half-edges around common vertex in 3d [closed]
I'm trying to figure out this problem for very long time and am no getting nowhere. I'm working on a simple 3d modeler that uses half-edge data structure.
Say I have non-manifold geometry where two ...
2
votes
1answer
95 views
Improve accuracy of mesh gradient?
So to make it simple. I currently use a method I found online to compute the gradient of a scalar field of a mesh.
To test how accurate this is, I made a sphere and followed the gradient direction of ...
3
votes
1answer
52 views
Mis understanding of the Heat Method
I have been trying to understand a paper in CG for a while, called the Heat Method by Ken
Many things have clicked but I don't fully understand it yet. In particular.
In the following $u$ is a vector ...
4
votes
1answer
75 views
Gradient descent (Not ML) on arbitrary meshes
So I am doing a gradient descent like algorithm on the surface of a mesh and I just noticed something:
The above is the geodesic gradient (the distance to a single vertex)
Look at where the ear ...
2
votes
2answers
119 views
Smart half edge iteration?
In my HE implementation, half edges are stored in an array. When I iterate over the edges, I color all the HE black, and when I do an operation on an edge (e.g edge splitting) I mark both the current ...
1
vote
2answers
105 views
Discrete Gradient?
I am trying to understand how to get the discrete gradient of a mesh that is being used as the input of some function $f$. In other words for every vertex $v$ there is a scalar quantity $s$ associated ...
1
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2answers
74 views
Heat Method (Crane et Al) How do we pick u?
The heat method is a very interesting paper for distance computation:
https://www.cs.cmu.edu/~kmcrane/Projects/HeatMethod/paperCACM.pdf
The idea behind the paper is that, heat travels along the ...
0
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1answer
57 views
Is the laplacian operator for meshes just the sum of the differences of neighbouring vertices?
I am starting to learn about the laplacian operator $\Delta = \nabla \cdot \nabla\phi(p)$
Which can be described as the divergence of the gradient of a scalar function $\phi$. This is equivalent to ...
1
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1answer
78 views
Approximating Geodesics in a half edge DS, how can I refine my mesh to get good approximations
I implemented Djikstra's shortest path algorithm to approximate Geodesics on arbitrary meshes. Djikstra's works, but I noticed a problem inherent to the discretization of my meshes.
Consider the ...
1
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0answers
54 views
The ploygon width parallel to the x axis as a function of the y ordonate?
Considering a polygon with n vertices as input.
I need to calculate the integral of the form
\[\int_A p(y) dA \] where $p(y)$ is a piecewise polynomial function of $y$.
May be if I could find the ...
0
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1answer
42 views
Fast and exact Geodesics on meshes, Backtracking confusion
The following is an excerpt from a 2005 paper on geodesics on triangular meshes, taken from section 3.5
In this case $p$ is a point on some arbitrary face in a mesh, $p'$ is a point on one of the 3 ...
0
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0answers
28 views
MMP Geodesic algorithm I need clarification
I am reading the 1987 paper on Geodesics on polyhedra and I am confused on something.
The paper states:
If $I1==NIL$, the channel is simply that part of $f’$ to the left of $\beta_2c_2$; and if
$I2==...
1
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1answer
54 views
Finding geodesics on a mesh?
What are some state of the art methods/algorithms to find geodesics on arbitrary manifold meshes?
3
votes
1answer
106 views
Are some 3D objects "solid"? Do they have internal density? If so, when, and in which file formats?
I am more or less a complete novice in the field of 3D modeling. I understand the basics of a polygon mesh and a texture; however, it was always my understanding that 3D models were, effectively, &...
3
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2answers
221 views
Why are texture coordinates often called UVs?
Is there some historical reason texture coordinates are often called UVs? I get that vertex positions are x, y, z but even OpenGL has TEXTURE_WRAP_S and ...
5
votes
1answer
850 views
How does UV unwrapping work?
I would like to project the triangles of my mesh to a 2D surface. I would like to minimalize the distorion, avoid breaking connected polygons if possible, and also maximalize the used space on the 2D ...
0
votes
0answers
65 views
How does on the fly LOD work?
In the Unreal Engine 5 tech demo, they mention, that there is no need to manually generate LOD levels for each model, because the on the fly LOD system will generate polygons from the original mesh, ...
1
vote
1answer
82 views
Has anyone found an analytic solution to the product of spherical gaussians from Xu et al?
In section 4.2 of this paper:
http://cseweb.ucsd.edu/~ravir/274/15/papers/a209-xu.pdf
Xu et al approximate the product of 2 anisotropic Gaussian distributions. I want to know if someone has found not ...
1
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0answers
69 views
Why does processing dense geometry consume less power than simple geometry?
In The Road to PS5, Mark Cerny states:
It's counter-intuitive, but processing dense geometry typically consumes less power than processing simple geometry.
Why is this the case?
0
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0answers
70 views
Consistent Video Depth Estimation from Monocular Lens to approximate LiDAR?
If the iPhone had LiDAR sensors, it would be possible to generate a 3D point cloud that you could theoretically use to furnish a 3D AR reconstruction of your surroundings. E.g. you could create an AR ...
2
votes
1answer
71 views
Off by one error when creating face indices
I seem to have an off by one error when creating the indices for the faces of a sphere and I can't understand where.
The exact problem is that when I try to calculate the normals of each face a dark ...
1
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2answers
518 views
Calculate normals from vertices
Assume you have a list of vertices and their connectivity information. (I.e you can find all the adjacent edges and faces to each vertex).
What is a good approach to calculate a normal from this ...
0
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1answer
67 views
How do you compute the winding number of a closed poly curve?
Pretty much the title, given a closed curve in 2D, defined by a set of points, and a point. What's the algorithm to calculate the winding number of that curve, point pair?
0
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2answers
407 views
Looking for a cylinder / axis-aligned box volume intersection test
Given:
An arbitrary circular cylinder (defined by startpoint, endpoint, and radius). An Infinite cylinder is acceptable as well, as long as it passes through those points and has the same radius.
An ...
0
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1answer
55 views
Determining shortest vector between a ray and an axis-aligned 3D bounding box (correcting a near-miss)
I have a situation where (due to floating point error) a ray that is known to hit a bounding box fails due to floating point error. (1e-8 or so)
Expanding the box is not an acceptable solution in my ...