Questions tagged [transformations]
Transformations are mathematical operations that can be applied to an object to change its scale, position and orientation.
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2answers
52 views
transformation from cartesian coordinates to spherical coordinates without calculations
Given this graph in the 3d cartesian coordinates i should figure out the spherical coordinates representation but without the use of calculations .
I've been trying to solve this the whole day but i ...
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2answers
63 views
Using transformations to get from A to B image
I try to solve this,
First, I used scaling: $Scale(S_x,S_y)=S(\sqrt 5,\sqrt 5)$
So, I enlarge the bottom of the house and the sides, to the same size of B image.
Later, I used rotation: $R(\theta)=...
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0answers
44 views
Rectifying the Environment Map (How it works)
Hello everyone I am currently reading a paper of Disney research, Zurich, for my exam, and I really don't understand a thing in this paper...
The main issue of this paper is to create a ...
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1answer
33 views
Define position and orientation in a local coordinate system
Suppose we have a world coordinate system W and a 3D model m1 defined in W. ...
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1answer
48 views
How to convert from Object space into World space (exercise from 3D Math Primer book)
This is not homework. I'm self studying Computer Graphics, using the book "3D Math Primer for Graphics and Game Development" (2nd edition). So there is the exercise 6 in chapter 3 which I can't figure ...
2
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1answer
49 views
My 2D translation matrix causes the box to be off screen when it shouldnt be
Now I know this isn't the way this is normally done so please bear with me. I am doing this this way so I know I have a solid conceptual understanding of everything that goes beyond example code.
I ...
2
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0answers
29 views
Transforming arcs and perspective change
I have a SVG with group of independent arcs that move around common origin.
On user event those arcs can change both their radii and start/end angles.
On other user event the user can change view from ...
2
votes
1answer
57 views
Bump mapping with triangles and height maps
I'm trying to add bump mapping to my ray tracer, and I'm currently struggling to add bump mapping to it, as I don't seem to get the transformations from texture space to world space correctly.
I have ...
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0answers
23 views
Understanding threshold finding in the Hough space in Python
I am following a tutorial on writing a Hough algorithm in Python: to my understanding it is very well written but I am new to computer graphic algorithms (not really used to thinking in terms of ...
3
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1answer
109 views
Need help with change of basis (world to camera frame)
I'm reading up on coordinate systems and geometric transformations but the change of basis topic still confuses me. I found this exercise but, honestly, I wouldn't know how to begin:
Given a world ...
2
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1answer
40 views
Composition of decomposed transformations
Say I have a scene graph, and each node has a scale, rotation, and translation. Can I combine these into a single scale, rotation, and translation?
2
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2answers
83 views
Rotate a model or a view with mouse input to produce intuitive results
I am writing 3D graphics software in Java using the LibGDX framework (which is a front-end for OpenGL), and am baffled by a transformation problem. How do I rotate the orientation of the camera or ...
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1answer
65 views
preserving z-values during projection?
Consider this figure for projection.
There are two equations that give value for the xp and yp coordinates:
$x_p=x.\frac{(z_{vp}-z_{prp})}{h}+ x_{prp}.\frac{(z-z_{vp})}{h}$ and
$y_p=y.\frac{(z_{vp}...
2
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1answer
45 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
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1answer
52 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 ...
0
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1answer
46 views
How to compute A and B in projection matrix
I'm trying to compute a projection matrix to transform from view space to NDC with a near clip plane at -1 and far plane at +1. The general form of this matrix (disregarding aspect ratio and focal ...
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1answer
95 views
How do I derive this transformation
If I had two right handed frames where one has vectors [i, j, k] and another with corresponding vectors [u v w], how would I derive the transform M[i j k] <-- [u v w] when applied to any point P in ...
2
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0answers
25 views
How can I register an articulated model to noisy predictions?
Given point sets $Y$ and $M$, I'd like to register articulated $M$ to $Y$ without changing the edge distances of $M$. The point correspondences between $Y$ and $M$ are known and points have a fixed ...
1
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1answer
67 views
Deciphering Affine/Projective Transformation Code
I've spent about 2 days trying to understand this piece of code (from here) that applies an affine/projective transformation to an image. I will link bits of the code that I'm struggling to understand ...
2
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0answers
44 views
What is wrong with my deformation gradient calculation?
I created two ellipses,$\hspace{150px}$,where the red ellipsis is as the blue one, except translated to the right and rotated by ${30}^{\circ} .$ Using rotation matrix,
$$
\left[
\begin{array}{cc}
...
0
votes
3answers
150 views
Rotation of a random unit vector at a point in 3D space by an angle
I have a scenario where I need rotate a vector ( unit vector) at a point in space by an angle along Z-axis. Is it possible to help me to understand a procedure to achieve this. I'm using vb.net ...
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0answers
43 views
How to apply scale, translate, rotate with different origin and get new rectangle coordinates
I was reading other questions in this topic but I couldn't apply any viable solution to solve my use case.
I have a crop area described with two dimensions (cropWidth, cropHeight)
I can easly compute ...
2
votes
1answer
39 views
Correctness or otherwise of the procedure for generating an orbiting camera in WebGl
I have to create a orbiting camera. I created the model of sun (a sphere) around (0,0,0) , triangulated and Phong shaded it. I would have a camera that goes around the sun thus an orbiting camera and ...
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0answers
712 views
General fixed-point scaling
For general fixed-point scaling problem, If I want to scale twice about a fixed point (x, y), I need to first translate the object so that fixed point coincides with the origin, then do the scaling ...
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vote
1answer
72 views
Rotating scene or complex object using center of AABB
All objects have two AABB (Axis Aligned Bounding Box), one in local space and one another in world space. The box in local space is calculated while importing scene from external source, and the box ...
3
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0answers
86 views
Linear bending of a mesh
I am trying to implement linear bending of a mesh by following what Alan H. Barr explained in his Global and local deformations of solid primitives paper (ACM link, Direct Link hosted on a faculty ...
4
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1answer
191 views
Canonical Space to Screen Space: Why do we have the strange -0.5?
When we convert from canonical space to screen space,
To map x from -1 to 1 to 0 to width,
...
1
vote
1answer
161 views
Curve rotation in GLSL fragment shader
I'm trying to figure out the correct math to rotate and translate a curve displayed in a fragment shader.
What I try to accomplish is to define a curve, for example a sine curve, in a local ...
1
vote
1answer
161 views
How do I build my tangent space matrix?
I'd like to understand how the process of building the "tangent space" matrix for normal mapping works. I'm following several tutorials, and other stackexchange questions, but I'm unfamiliar with the ...
1
vote
0answers
36 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 ...
3
votes
1answer
477 views
Ray tracing: transforming ray to object's local space for intersection test
Im writting a raytracer, for which I want to be able to test intersections with implicit surfaces (in my case spheres). Without applying any transformation it works great, but I would like to upgrade ...
1
vote
1answer
108 views
What is the algorithm used in pbrt-v3 for triangle intersection?
Where's this algorithm come from? Any references?
And a specific question, when the authors compute the transformation from world space to ray-triangle intersection coordinate space, what's the ...
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vote
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 ...
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vote
1answer
70 views
Back and forth rotation on Y-axis
I want to write code for a cube rotating 10 degrees back and forth on its y-axis in an OpenGL application. Right now I have this written in my display method, however it depends on processor speed, ...
2
votes
1answer
59 views
Do normals in obj files have to be changed into eye coordinate before being used?
Obj files give pre-calculated normals which are in model coordinates. So I wonder if they have to be transformed into eye coordinate (where I use them to calculate lighting)? I'm thinking yes because ...
2
votes
1answer
432 views
Why does this gl_FragDepth calculation work?
I am raytracing in GLSL. My gl_FragDepth calculation wasn't right, so I did some hunting and found this solution (P is the world-...
1
vote
2answers
109 views
Is there something wrong with a column camera matrix?
I am writing a simple ray tracer. I was working on my camera matrix when I encountered a problem. When I changed the look vector, so that it headed down, the image, which was supposed to go up, ...
1
vote
1answer
101 views
What technique would I use to create fake 3d walls as seen in Realm of the Mad God
I wanted to make a little demo for a console with Realm of the Mad God esc graphics to brush up my C and SDL skills.
One problem I'm running in to is creating the 3D walls.
The console I'm ...
1
vote
1answer
63 views
Image warping using pixel normals
I want to insert a logo into an RGB image with proper 3D transformations. I can get the estimated pixel normals of this image using the code here: https://github.com/yindaz/surface_normal. Pixel ...
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0answers
147 views
Octahedral mapping for Spherical functions
I guess most of you are familiar with environment maps, they represent distant lighting distribution, and are used to render objects given their BRDF or SVBRDF distribution. Many papers map the ...
5
votes
1answer
242 views
why is translating in 3D space the same as shearing in 4D space?
I was reading "3D Math Primer for Computer Graphics and Game Development" and there was something the author had said that I thought was particularly interesting, he stated
It is important to ...
4
votes
1answer
127 views
How to obtain generalized barycentric coordinates for n-sided polygon?
Quadrilateral linear basis functions(generalized barycentric coordinates) are defined as:
What are the steps to calculate the above functions?
Is it possible to obtain basis functions for a 5 sided ...
1
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0answers
114 views
Composition of an .obj file
Using an iPhone X, I can get a mesh of the face (using ARFaceGeometry), which I can output as an .obj file using ...
3
votes
1answer
107 views
How to calculate camera distance so that after projective transformation a quad is filling the whole screen
First of all, I'm using OpenGL and GLM.
Now, I have a square perpendicular to the z-axis and centered around it. Let's say that it has Z-value (offset along the Z-axis) X. Now, I want to set up a ...
2
votes
2answers
328 views
OpenGL : How to rotate an object around viewing space x-axis
I have an object(cow).
This cow was translated and rotated(with arbitrary axis) in the modeling space for several times.
And I can't know how much cow is translated or rotated.
Only I can obtain is ...
3
votes
2answers
39 views
How to get the length of paths in an given font/character
I wan't create some LED-rope text, using some script font, like the following:
For this I need somewhat estimate the needed length of the LED-rope for the given letter (or combinations of letters).
...
4
votes
2answers
74 views
Supporting multiple camera types in a deferred renderer without specializing the shaders or in the shaders
Perspective Camera
A (row-major) perspective transformation matrix has the following format:
$$\begin{align} \mathrm{T}
&= \begin{bmatrix}
\mathrm{T}_{00} &0 &0 &0 \\
0 &\...
3
votes
1answer
1k views
OpenGL : How to translate an object with it's own axis
I'm working with OpenGL to try to rotate / translate my 3d object : a cow.
The requirement is simple :
If I toggle key 'r'. The cow spinning around and random axis.
If I drag the cow with mouse, it ...
3
votes
1answer
102 views
How can I implement GIMP's “Colorize” function?
I have an RGB pixel that I'd like to colorize in my program (I'm using GLSL) very similar to how the GIMP "Colors > Colorize" function works.
In my program, I can easily convert between RGB and HSV. ...
1
vote
1answer
46 views
How to rotate an object around any axis if i have just local x and y?
I have just two local axis to rotate a 3D object: X (horizontal) and Y (vertical). How to make from this 2 local axises for example a global Y rotation or a Local Z rotation? What math magic do the ...
