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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Translate the camera with Pan gesture (when it is rotated )
I am new here
I am not good in math
SO what I need is I need to translate the 3D camera with Pan gesture on 2d Screen
With below code it is working
But if camera has some Euler Angle (rotated ) then I ...
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23 views
Using 2D point/polygon algorithms on polygons lying on a arbitrary plane
Is there an efficient method to apply 2D point/polygon algorithms on general planar points. For example, I need to triangulate a polygon where the input is a list of ordered points. The algorithm ...
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2answers
60 views
Why is browser-resized image crispy and manually-resized image blurry?
I've come across this problem several times now and I can't really understand what causes it; my background is in Wordpress, not really in computer graphics.
I hope this is the right place to ask, I ...
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1answer
43 views
Path tracing: How to ensure we are sampling a direction vector within the visible hemisphere of a surface?
Given a surface Normal vector of an intersection point, how can one generate a random direction vector that is guaranteed to be in the visible hemisphere? The way I ...
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1answer
91 views
Transforming a ray from camera space to world space
I am writing a Raytracer and generating rays from the camera. I have a working program but slightly confused about the linear algebra concepts involved in transforming the ray from camera space to ...
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1answer
36 views
Rotate a Bitmap with Shearing
I am rotating a bitmap using the three shear algorithm documented in these articles [1][2].
From about 0-90°, the quality is acceptable, but beyond that it gets progressively more distorted until it's ...
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1answer
29 views
rotate objects like a trackball
I know how to rotate objects around the center and there are rotation matrices for that as well, but, how do we rotate the object like a trackball, below is the example:
firstly I rotate around the y ...
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1answer
38 views
Rotating a Bitmap
I would like to rotate an bitmap image using math. I have two issues with my current implementation: the pixel-by-pixel rotation of the copied bitmap is extremely slow and it is leaving gaps between ...
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77 views
Help me understand the derivation of this tangent space to object space matrix
I was trying to follow this http://foundationsofgameenginedev.com/FGED2-sample.pdf
But had problem understanding formula 7.33.
$$p_i-p_j=(u_i-u_j)\mathrm{t}+(v_i-v_j)\mathrm{b}$$
* $p_i,p_j$ being ...
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39 views
3D Bouncing Cube
I'm trying to write a little program with a bouncing cube but I can't find the right x, y, z and angle for it. I have these lines:
...
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75 views
Model View Projection Matrix Multiplcation Order
I'm working on a simple software renderer and have a working implementation so far. I'm curious as to why it's actually working since I would expect the multiplication ordering for my world, view and ...
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41 views
Matrix transforming with translation/rotation/scale at center of screen
I'm trying to create a camera using matrix transforms, the gist as follows:
...
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1answer
52 views
THREEjs: updating an object's matrix doesnt change it's position and rotation params
I want to set a transformation matrix to an object upon creation and then control it by position, rotation and scale, but while changing the matrix does change the object in world space, it's position ...
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22 views
How to “preserve texture” when transforming vertices
Maya has a feature called preserve texture. It allows you to transform vertices of an object and basically have the texture "stay in place" in object space. Say I have a plane with unwrapped ...
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1answer
34 views
Could the Tetradic color pattern be expanded to allow /dev/random be “pretty” for cryptographic key purposes?
Is there a way to take a random value (or set of values), and cause them to create a "pretty" pattern (as a thumbprint), and that array of thumbprints might have a rendering mask on just for ...
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0answers
44 views
What's the name of the transformation that can remove horizontal convergence from a picture?
Say that you are taking pictures from a street like this one:
As you can see, the picture is taken perpendicular to the direction of the street.
The problem is that cars at the left look as if they ...
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1answer
87 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 ...
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1answer
114 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, ...
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79 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 ...
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1answer
52 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 ...
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1answer
128 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 ...
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0answers
28 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 ...
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63 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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29 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 (...
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1answer
67 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. ...
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2answers
166 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 ...
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57 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 ...
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46 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" ...
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0answers
100 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 ...
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3answers
152 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, ...
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1answer
92 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 (...
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58 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 ...
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1answer
227 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 ...
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0answers
203 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 ...
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1answer
254 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 ...
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2answers
599 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 ...
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0answers
83 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.
...
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0answers
56 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 ...
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1answer
169 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 ...
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1answer
116 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....
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1answer
3k 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 ...
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2answers
200 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
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1answer
345 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 ...
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1answer
73 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
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1answer
125 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 ...
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2answers
352 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
82 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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1answer
114 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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2answers
2k 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 ...
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1answer
99 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 ...
