Questions tagged [geometry]
The geometry tag has no usage guidance.
1
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1answer
22 views
How to scale primitive shapes [in Blender] so that they are within a [unit] sphere?
I wonder how is it possible to scale all shapes so that they are within boundaries of a [unit] sphere? I know how to do this for a cube: if radius of the sphere is S...
4
votes
1answer
108 views
Do straight lines always remain straight when projected with a perspective camera?
If I have a straight line in 3D space and I use a camera matrix to do a perspective projection into a 2D plane/screen will the resulting line always be straight too? If I project the start point and ...
2
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0answers
51 views
Intersecting Frusta
I am trying to determine whether two frusta intersect in 3D space and to quantify this intersection as a percentage of one frustum volume (eg. 100% intersection meaning that the two frusta occupy the ...
1
vote
1answer
92 views
Texturing an “infinite” plane
I am rendering an infinite plane as described in the following answers:
https://stackoverflow.com/questions/12965161/rendering-infinitely-large-plane
https://stackoverflow.com/questions/7380250/how-...
3
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0answers
85 views
How can you avoid thin triangles in a parametric shape in a smart way?
I have created a closed 3D mesh using a parametric function. The shape is constructed by taking an arbitrary closed b-spline and scaling it based on one of the parameters (similar idea to a parametric ...
4
votes
2answers
85 views
Should you measure mesh complexity in triangles or vertices?
I have seen people using either vertices or triangles as a quick heuristic to estimate mesh memory usage and mesh rendering time.
I always thought vertices were better, because the number of vertices ...
7
votes
2answers
780 views
Why are oct trees so much more common than hash tables?
When reading papers I commonly find Oct tree implementations of geometry representations to sort the data. However whenever I think about the problem hash tables seem better overall.
Hash tables have ...
2
votes
1answer
70 views
Given a picture of a unit square at an arbitrary angle and position, how can I reconstruct the distance and orientation?
To simplify, assume faces and corners of the square are labeled and the camera lens if whatever makes this simplest (a 90 degree field of view projection?)
The application: using a known and labeled ...
3
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0answers
157 views
ray-triangle intersection precision - c++
I'm building a software renderer but I think there might be some problem with my ray-triangle intersection accuracy.
I implemented the algorithm referring to ...
2
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1answer
48 views
What is the equivalent of rotation matrix in Euler angle space for Quaternions?
I have to load a mesh in Blender (which uses Z and Y as up and forward axes), modify it and export it (with setting up and ...
1
vote
1answer
56 views
How to rotate a shape in another 3D software so that the rotation matches with the rotation in Blender?
I import a mesh in Blender, export it with setting axis_forward='-Z', axis_up='Y', import in NVIDIA's FleX, rotate it and store it on disk; I call this mesh ...
3
votes
1answer
1k views
How to convert Euler angles to Quaternions and get the same Euler angles back from Quaternions?
I am rotating n 3D shape using Euler angles in the order of XYZ meaning that the object is first rotated along the X axis, then Y...
5
votes
1answer
66 views
How to randomly draw Quaternions within a specific range of Euler angles for rotation?
I am pretty new to Quaternions so please bear with me. I want to draw random Quaternion samples so that their Euler angle equivalent would range within [-30, +30] ...
2
votes
1answer
110 views
Computing perspective directly
Assume the screen is axis aligned with origin at 0 and there is absolutely no view transformation.
in other words we will simply try to project the model onto the screen plane following perspective. ...
1
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0answers
37 views
Simulating vanishing points shader
How do I create a vertex shader that allows to choose 3 non aligned direction vectors and then allows to morph all vectors positions such that every vertex is remapped so that two vertices that are ...
1
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0answers
47 views
Sorting my geometry for alpha testing
Here is my predicament. I am trying to draw a multitude of dots that leave trails behind them real time. Heres the difficulty, that line fades. Each dot line has a defined z position and the goal ...
2
votes
1answer
40 views
Remove orphaned geometry after Constructive Solid Geometry operation
I have used a library to perform a Constructive Solid Geometry difference operation, which has left me with orphaned geometry as well as imperfections.
Is there an approach/algorithm that will allow ...
0
votes
0answers
45 views
How to ensure that the raytrcing coordinate system is teh same as the projection one?
I have 2 shading models right now, one is using voxels the other one is the standard projection absed renderization method.
Putting them side by side I have noticed that no matter what I do one is ...
0
votes
1answer
41 views
Pathtracing line and point primitives?
So I'm in the midst of implementing a path-tracer. I have chosen to use Assimp library to load models and scene information.
According to it, it will provide mesh data and meshes may contain point, ...
0
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0answers
11 views
Where on the .obj or .mtl files is the information needed to find the texture associated with a wavefront file?
I've downloaded the sponza scene, and I will use it to develop multi object rendeirng on my engine.
I can load the mesh just fine. But the mesh is currently monochromatic (looks 3D thanks to blinn ...
1
vote
0answers
26 views
How are non-triangular wavefront meshes handled?
I have a wavefront loader, however it only works with triangular meshes.
I have been trying to think how to handle faces with arbitrarily many vertices but I have no idea how they are to be handled ...
1
vote
1answer
62 views
how to draw mesh equal distance from irregular shape geometry bounding box
I am given an irregular geometry shape with its vertices, bounding box information.
How to draw a smooth mesh equal distance from that irregular geometry shape's bounding box?
Please refer to the ...
3
votes
1answer
79 views
Path Tracer - Model loading Libraries?
so I am in the process of making my own GPU path tracer based on OpenCL as part of my bachelor thesis. I have already made a CPU and a GPU ray tracer based on OpenGL compute shaders but all I have ray-...
1
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0answers
38 views
Transform a cube in a truncated pyramid
I have to calculate the modeling transformation that transforms a cube of side=1 centered in (0,0,0) in a rectangular truncated pyramid of height=2,sides of basic rectangle equals to 3 and 2, sides of ...
4
votes
1answer
84 views
Subdivide a triangle along its UVs
I'm looking into a problem that first occured very trivial to me, but i got stuck and it's becoming a major issue right now. I'd like to subdivide a triangle by its given UVs, e.g. if the UVs are ...
3
votes
1answer
278 views
Delta angle of two vectors about positive x axis
How do I calculate angle C?
I can only know what angle between vector and x positive vector {1, 0}
Angle between green and red is 60 degrees.
Angle between blue ...
4
votes
1answer
125 views
Triangulation of vertices of an ellipsoid
I have the parametric model of an ellipsoid like this:
\begin{cases}
x=a_1\,cos \,\eta \:cos\,\omega & -\pi\leq\omega\leq\pi \\𝑦 = 𝑎_2\,cos\,\eta\:sin\,\omega \\ z=a_3\,sin \,\eta & -\frac{...
1
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0answers
46 views
Tanget plane of an image
My problem is about tangent plane. I have an image (m by n). I obtain surface normal vector using machine learning methods. Then i would like to obtain tangent plane for this surface normal.
To ...
1
vote
1answer
131 views
What's wrong with my computation of the intersection of a ray with a sphere
I am learning GLSL and trying to raytrace a sphere.
Here is a fragment shader. It correctly discards fragments which are not on the sphere, but when I try to calculate the point of intersection (and ...
3
votes
1answer
51 views
calculating size of rectangle which fully obscures a sphere
I am learning GLSL and want to raytrace a sphere. I am rendering rectangles which sit between the camera and sphere, and do a ray-sphere intersection test in the fragment shader. It almost works:
As ...
1
vote
2answers
336 views
Euler Angles - Gimbal lock, why non-orthogonal axes
Already asked this question on mathexchange but didn't got any promising answers so posting it here Since I'm from a CG background.
I really can't understand how and why gimbal lock occurs using ...
1
vote
0answers
37 views
Which vertices to use to create side of model
I hope I'm asking on the right StackExchange site. Apologies if I'm not.
I want to generate 3D triangulated models of optical lenses, circular in shape. I can create the meshes for the front and back ...
3
votes
1answer
101 views
Heirarchy in Euler rotations
Why is there necessarily a hierarchy in Euler rotations?
For example I need to decide that I want
x to affect y and z
z to affect y
y to affect nothing.
What if ...
1
vote
1answer
65 views
How to obtain a parametric equation out of a part designed in Autodesk Inventor?
Whenever you make a part in inventor, the software calculates de properties of the whole body given a constant density. Then, automatically, it shows the inertial tensor. As you can recall from math, ...
3
votes
1answer
119 views
Rounding a corner formed by Arc and Line
Given shapes like these, which contain just Arcs and lines, I want to round all its corners with certain radius. I know the vertices of the lines & arcs these shapes.
I can round the corners of a ...
1
vote
0answers
37 views
3D reconstruction using 2D matched points
I have 2 images, called left and right images. I have some matched points $[c_l,r_l]$ and $[c_r,r_r]$ in both of them (these points are in pixel coordinates).
For a 3D point in the real world, they ...
1
vote
1answer
62 views
Are there LOD Algorithms that work through removing objects?
I want to implement a LOD algorithm that reduces the number of objects rather than the number of vertices of the objects.
Imagine a forest, then close up I want to see all the trees but moving away ...
7
votes
1answer
227 views
Visualizing the Lane-Riesenfeld Algorithm
Ok so, I keep reading papers about this and non of them have pictures. The lane Riesenfeld algorithm provides a way to subdivide set of points with B-spline conversion.
The quesiton is simple HOW? If ...
5
votes
1answer
539 views
Rounding the edges in a mitered line segment inside of a fragment shader
As some of you may know drawing line segments between sets of points is really difficult especially when you want wide lines or variable widths.
Because I am looking to draw a few hundred of these ...
1
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0answers
33 views
Program to visualize geodesics and linear projection of an ellipsoid simultaneously
I am trying to solve a problem in computer graphics but to do it I need to be able to see a comparison of geodesic lines and straigth line projections on the ellipsoid.
I have not been able to ...
6
votes
1answer
182 views
Logarithmic spiral with equal vertex spacing, what equations?
I need to draw a logarithmic spiral (or close approximation) whose vertices are equally spaced, such that the lines between any two consecutive vertices are of equal length.
(Actually, that spiral is ...
2
votes
0answers
103 views
How is it possible to generate geometries using space folding?
There is a TED presentation, where we see really good looking geometries, which are generated using space folding.
I get the general idea, that we start from a basic geometry like a cube, and then ...
4
votes
1answer
616 views
What's the difference between geometric surface normal and shading surface normal?
In my opinion, geometric surface normal is the cross product of triangle edge vectors, and shading surface normal is the interpolation of the predefined normals at the three vertexes.
I used Mitsuba ...
1
vote
1answer
52 views
Is it possible to draw the intersection of two squares of known dimension using only x,y coordinates and without an if statement?
Say I have two squares, both 10x10, with some small, unknown overlap.
Is there a way to draw the intersection of these two squares using the width, height and x,y coordinates of each square, while ...
1
vote
0answers
100 views
Algorithm for clipping convex quadrilaterals
I'm dealing with hardware that uses quads as its polygonal primitive. Not triangles. A triangle can be expressed by setting 2 of the 4 vertices equal to each other for a degenerate quad.
For the 3D ...
-3
votes
1answer
57 views
constrain based dynamic geometry generation [closed]
I have a bounding box of 1000m x 1000m. I randomly generate 10000 points (sites) inside it. Now, how can I create 'n' polygons (geometries) within the bounding box based on a given constrain.
The ...
7
votes
1answer
178 views
List of triangles to minimum amount of convex polygons
I'm in search for an algorithm that takes the left side of the following graphic as an input and outputs a minimal amount of convex polygons as seen on the right side of the graphic.
The input mesh ...
1
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0answers
41 views
Rectangle bounds of isometric object to isometric bounds
This might sound confusing, but this is what I'm trying to achieve:
project to:
I already have an algorithm in my mind, where we simply detect the corners touching the Cartesian rectangle and ...
4
votes
1answer
157 views
Convex non simple polygon?
Existence question: Can there exist a convex polygon witch is not a simple polygon?
2
votes
2answers
621 views
Extract visible vertices from a 3D geometry model
Let's assume we have a 3D model consisted of XYZ-formatted vertices (such as point cloud model). My problem is given the position and normal of camera or camera ...
