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Questions tagged [geometry]

The tag has no usage guidance.

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44 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. ...
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0answers
34 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 ...
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0answers
38 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
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1answer
37 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 ...
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0answers
31 views

Dragging an object on a plane with respect to the camera

this is a long description but I hope the solution is simple: I have a 3D pointCloud with a vtk box (displayed at 0,0,0) and I want to drag the box on the XY plane with my mouse cursor (Zero movement ...
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0answers
42 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 ...
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1answer
35 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, ...
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0answers
8 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 ...
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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 ...
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0answers
21 views

Expressing dot density in a scene in terms of visual angle versus cm

When rendering random dot scenes, I sometimes see the literature express density as $n\ dots/degree^2$ of visual angle. Is there a way to convert this density to $dots/cm^2$? Or when I read that a ...
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0answers
26 views

How difficult would it be to customise Google Maps

How difficult would it be to customise Google Maps to display roads like they were biological veins? Vein appearance (width)/promotion would be exaggerated according to road classification. Where ...
1
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1answer
49 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 ...
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1answer
75 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-...
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0answers
33 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
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1answer
78 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
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1answer
132 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
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1answer
100 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{...
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0answers
45 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 ...
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1answer
97 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
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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 ...
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2answers
198 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 ...
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0answers
36 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
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1answer
97 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 ...
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0answers
27 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, ...
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1answer
94 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 ...
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0answers
33 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 ...
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1answer
57 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 ...
6
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1answer
192 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
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1answer
303 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 ...
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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
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1answer
130 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
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0answers
100 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
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1answer
434 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 ...
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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 ...
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0answers
79 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 ...
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1answer
54 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
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1answer
121 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 ...
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0answers
39 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
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1answer
128 views

Convex non simple polygon?

Existence question: Can there exist a convex polygon witch is not a simple polygon?
2
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2answers
387 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 ...
5
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1answer
202 views

What is the name of toroidal 2D space

I have a 2D space of dimensions (X,Y) with toroidal properties : In this space, when a point A(x,y) change it's position such as x is getting > X or < 0, then x becomes (x % X). So when the point ...
5
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1answer
87 views

Best way to group 3d points into planes, if any

If I have some 3d points, how can I discover parallel planes within them (not just arbitrary planes). I want to know how many "levels" or "floors" something can travel within, after it has done so, ...
4
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1answer
112 views

The constructor of hyperboloid in pbrt-v3

The book omitted the explanation of the constructor of hyperboloid. Could someone give some explanations about: Why the arguments are two points? What are the meanings of ah and ch? Why is there a ...
4
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1answer
121 views

Calculate a rotation around an arbitrary axis

Suppose I have two 3D triangles before & after a single rotation around an unknown axis. How would I go about finding this axis?
5
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1answer
134 views

Calculate Transformation between two point sets - but with constrained Degrees of Freedom

How can I calculate the rigid transformation [R|t] between two 3d triangles, but restricted to a given N degrees of freedom (for N = 1..6) ? I know for N=6 I can get a least-squares solution via SVD ...
4
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1answer
458 views

Bevel/Chamfer algorithm for arbitrary 3D mesh

I can't find any paper about a bevel/chamfer algorithm for 3D mesh. Bevel has a lot of special cases (corners, different bevel profile, bevel larger than a face). I am looking for robustness. Do you ...
1
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1answer
151 views

Test if polygon edge is facing another polygon

How do I test to see if a polygon edge is facing another polygon? For the edge being tested to return true, the edge needs to be facing a polygon which has a different attribute than itself. In this ...
7
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2answers
177 views

Sampling against geometry normals

I am writing a basic raytracer and have implemented normal maps. However, when using normal maps, sometimes the rays generated are opposite to the surface's geometry normal, so that the rays are ...
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1answer
79 views

Mirroring avatar

I have a skeleton (in asf/amc format), from CMU's mocap database. I'm using python, no libraries yet. (Blender in python mode doesn't work properly for this, as far as I know.) I want to mirror the ...
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0answers
122 views

Transform a centered isosceles trapezoid in a rectangle in 2-D

I must convert a isosceles trapezoid to a rectangle in 2-D with a shearing transformation (or with 2 shearing transformations). The isosceles trapezoid is centered in the origin of axes. It is right ...