Questions tagged [transformations]
Transformations are mathematical operations that can be applied to an object to change its scale, position and orientation.
167
questions
3
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1answer
54 views
Interpolate vertex attributes with $z$ AFTER homogeneous divide
Usually, if we want to interpolate some vertex attributes, say $A_1$, $A_2$ and $A_3$, we have to first divide them by their corresponding $z$ in view space, then we interpolate them using barycentric ...
2
votes
1answer
92 views
Transformations and change of basis in CG
Sometimes in CG literature a transformation is equated to a coordinate system change. This is fine as long as the transformation includes only a rotation and a translation. When scaling is involved, ...
1
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0answers
78 views
Why does my self-written rendering engine make further away objects look larger?
I am writing a very simple rendering engine. I have already made a few tests, but somehow the images it creates look wrong. Objects that are further away from the camera look larger than objects ...
0
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1answer
47 views
Converting Vertex and Index buffers to a File Format
I have many sets of vertex and index buffers that I’d like to render on to the screen. Ideally each model in different locations with-in world space. I’m actually doing a statistical study on spatial ...
3
votes
1answer
64 views
How to keep an object constant in screen space?
If you open the modern Blender UI and select for example scaling, and then you use the scroll wheel to "zoom" (move the camera along the radial axis). You will notice that the size of the 3D
widget ...
0
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0answers
23 views
How to transform x-y-z red-green-blue arrows and draw them on 2D screen?
I'm making a raytracer and want to print debug arrows
Blender example:
Old version of 3d max:
How do I do the same having camera forward, up and right vector?
I think I need some kind of matrix ...
0
votes
0answers
53 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 ...
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0answers
24 views
Does rotating object inside unit cube [-1,1] by homogenous matrix move it outside unit cube
I am just trying to rotate my pointcloud object which is inside the unit cube ([-1,1] in all x,y,z axis). What I did is use the basic rotation matrix from wiki and extend it to homogenuous 4x4 matrix (...
0
votes
1answer
59 views
Apply Projective Transformation 2D Rectangle
I want to write code from scratch about Projective Transformation in order to apply this transformation to 2d rectangular. I searched about this transformation, but I could not figure out completely. ...
0
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0answers
46 views
Rotation around local axis
I am trying to understand rotation and I come across the scenario of rotation with respect to the object itself.
One strategy that makes sense to me is that I would translate and rotate one of the ...
0
votes
2answers
72 views
What kind of transformation when the aspect is changed for a rotated shape?
I have a geometric shape (assuming that is a rectangle). I want to rotate it about it geometric center by an angle of 45° and plot the result using matplotlib with an equal aspect ratio, I get ...
0
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0answers
47 views
Estimate 3D cube pose after camera rotation
I have some photos of 3D cube. I also know the 3D pose of the cube in each photo (yaw, pitch, roll).
I want to estimate the new pose (yaw, pitch, roll) of the cube after performing 2D rotation to the ...
0
votes
0answers
38 views
Transformation for aligning 3D object with reference frame of 3D turtle graphics
The problem
I'm using a 3D extension of the well-known "Turtle graphics" to draw plants. My system works by maintaining a position $\vec{p}$ and three vectors:
The heading $\vec{H}$
The "up" ...
1
vote
0answers
56 views
Apply transformation to single vertices in OpenGL in order to deform mesh
I'm making a 2D cell simulation game.
The mesh for my cell is basically just a manually-generated triangle fan that looks like this.
I would like to reproduce the wobbling/vibration effect on the ...
4
votes
3answers
101 views
Visualize the interpolated unit quaternion on the surface of the unit sphere
My major is mechanical, please forgive me for asking questions that may seem trivial to you.
First, I'm reading the following paper:
Dam, Erik B., Martin Koch, and Martin Lillholm. Quaternions, ...
0
votes
1answer
80 views
Compute Speed of Spheres in 3D animation
I have created two animations:
One where a "camera" moves towards the spheres creating an optic flow (1st GIF).The code can be found here.
One where spheres move randomly in a 3D coordinates space (...
0
votes
0answers
32 views
What quad will fill the screen, which can be inverse-projection-view transformed to map to the near frustum plane?
I've been experimenting with raytracing using GLSL. I had success rendering a cube which encloses the object.
Now I want to do a full-screen raytrace, and I want to construct a quad which covers the ...
0
votes
1answer
93 views
Can pixels on the image plane be mapped to world space coordinates?
I'm trying to learn the fundamentals of 3d computer graphics by writing a toy framework in WebGL.
I'm currently working on mouse based camera controls. There are plenty of good resources in the ACM ...
1
vote
0answers
160 views
Help with understanding the look-at function (the view matrix)
I've been reading this article about the look-at function. I don't understand the part when they're trying to inverse the matrix N.
They say that R is orthogonal because all its row and column ...
2
votes
1answer
159 views
Use glTranslatef and shaders?
In newer OpenGL it's encouraged to use shaders and pass the model-view-projection as parameters. But what if I drew a complex object, and wanted to translate/rotate it and draw many copies?
For ...
0
votes
2answers
518 views
How can i wrap the earth image around a 3D Sphere using OpenGL, GLFW, GLAD, GLM?
Please help me out with this thing and currently i am a little more than a beginner so please tell me in that context. i don't need any obsolete methods for creating this like using GLUT or GLEW.can ...
0
votes
0answers
63 views
Moving a sphere in a basic ray tracer
I have written a really basic ray tracer. It generates primary rays and sets the colour of the pixel to the colour of the object that I have set myself. The code for which can be seen below.
...
0
votes
0answers
34 views
How to find matrix that projects 3d points into 2d plane centered in the origin?
I have a list of 3D points defined by Cartesian coordinates, i.e. [(x1,y1,z1), (x2,y2,z2), ..., (xn,yn,zn)]. I want to project them to a 2D plane which has origin in the center (0,0,0) but which is ...
4
votes
1answer
110 views
What are affine covariant regions
I am trying to understand this seminal paper. I read this post on what affine transformations and my understanding is that affine transformations are transformations that preserve parallelism of lines ...
0
votes
1answer
93 views
Inflate 3D mesh into sphere
I am after a simple (not necessarily efficient) algorithm to "continuously" transform a closed surface mesh into a sphere.
It seems that Blender is able to do this quite well: https://docs.blender....
1
vote
1answer
2k views
What is the difference between world coordinate, viewing coordinate and device coordinate in computer graphics?
The 2D pipeline involves with the construction of world coordinate scene followed by converting world coordinate to viewing coordinate, then transforming viewing coordinate to normalized coordinate ...
1
vote
2answers
157 views
How to calculate interpolation between multiple skeleton poses?
I found out that I should use spherical linear interpolation to blend two poses of a joint. I cannot find what to do if I have hundreds of poses to blend except applying the SLERP iteratively.
What ...
4
votes
1answer
217 views
Camera Model View transformation in Ray Tracing
I am implementing my own simple ray tracing and I came across some sort of confusion. When defining the verticies in the world I multiply them by the modelView transformation system (the matrix ...
0
votes
1answer
59 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...
0
votes
1answer
113 views
Ray tracing the next week: understanding Instances
My question is not about the code, but it's about the approach used by the author Peter Shirley (and apparently common practice in ray tracers) of handling Instances. To understand the question it's ...
0
votes
2answers
237 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 ...
0
votes
2answers
77 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)=...
0
votes
1answer
60 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. ...
1
vote
2answers
810 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
votes
1answer
81 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
votes
0answers
34 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
393 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 ...
3
votes
1answer
480 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
votes
1answer
123 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
votes
2answers
374 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 ...
1
vote
1answer
215 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
votes
1answer
177 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 ...
0
votes
1answer
72 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
votes
1answer
115 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 ...
0
votes
1answer
99 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
votes
0answers
27 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 ...
2
votes
1answer
171 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
votes
0answers
47 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
371 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 ...
1
vote
0answers
283 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 ...
