# Questions tagged [projections]

Questions about the conversions of a 3D model to a 2D model.

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### Clever projection of point onto triangle?

I know of at leas tone way to project a point onto a triangle. Project onto the plane, check barycentric coordinates, if outisde triangle, project onto the 3 segments, check distance, retain closest ...
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### Why is my cube triangle glitching?

This is driving me absolutely insane, I am battered and defeated I'm following a tutorial on projection matrices and everything seems good......... except this ONE polygon. I have checked all 3 ...
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### 3D projection Axis inversion problem (Java/Processing)

Unfortunately, I always had problems with math and was never good at it. I'm currently trying to combine math with my knowledge and my passion for programming. Brief introduction: In math, we have ...
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### Screen space to texture space transformation

I've built a deferred renderer that is able to do deferred decals, now I want to be able to bake that into textures. I have a texture (so screen space) that holds a deferred screen space decal that ...
62 views

I have a projection calculation which maps points from 3D space to pixel (image) space, and I want to use it as instead of the standard MVP projections in a vertex shader. In the image below the lower ...
1 vote
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### Finding Camera projection matrix from known input and output

Lets say I have a rectangle with known coordinates in 3D scene, and I'm projecting it using pin point camera to the plane (screen). You can imagine it deforms on the screen per camera transformation ...
14 views

### Object picking for a non-scaled graphic in a scaled scene

I have a visual 2d representation of a coordinate system, and a bezier graph with control points represented using a circle graphic. I need to be able to scale the coordinate system including the ...
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1 vote
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### What projection matrix and world transformation do I need to have an isometric projection?

I'm doing my own engine in college to display a wireframe on screen with an isometric projection but I literally can't find any literature about maths behind doing it by hand just for game engines ...
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### OpenGL old-style diffuse shading producing unexpected effects

Question: What is going wrong with the shape of the contours of constant illumination in the below picture ? Detail: Although Lambertian shading might be ill-regarded because it exposes the hard edges ...
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1 vote
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### Difference between 2D and 3D pipeline

2D transformation and viewing: The camera projects the 2D world co-ordinate $(x_w, y_w)$ on its projection plane which co-ordinates $(x_v, y_v)$. 3D transformation and viewing: The camera projects the ...
178 views

### Parallel projection is special case of perspective projection

I synchronized with @David k's first and second answer regarding perspective and parallel projection. From the first question I understand that the image on the screen is typically described in ...
383 views

### Difference between transformation and projection? [closed]

We know that world coordinates $(x_w, y_w)$ transform to viewport coordinates $(x_v, y_v)$ which are the physical device coordinates. And during projection, any point $(x, y, z)$ projects to $(x, y)$ ...
1 vote
75 views

### Why shearing coefficients multiplying by y? [closed]

We know that shear is transformation that distorts the shape of the object. Shear relative to X-axis that is $y=0$ line can be written as: $x'=x+sh_x.y, y'=y$ My question is why $sh_x$ is multiplying ...
1 vote
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### Difference between perspective and parallel projection [closed]

We know that in orthographic Projection Projectors (projection vectors) are perpendicular to the projection plane. And in Perspective Projection Object positions are transformed to the view plane ...
1 vote
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### Why are vanishing point and centre of projection the same [closed]

We know that in perspective projection object positions are transformed to the view plane along lines that converge to the projection reference (center) point like this: But many websites say that COP(...
184 views

### $P^2$ vs projection plane

I want to explain what I understood of definition of the two things. Projection plane: The general processing steps for modeling and converting a world coordinate description of a scene to device ...
1 vote
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### What should be considered the origin of a ray used for object picking with perspective projection

I need to create a ray to pick objects in 3d environment using cursor. I'm not going to go into detailed math for this question. There's tons of information on that. In short terms, for orthogonal ...
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### How does 3D graphic software adjust for distortion inherent in perspective projection?

As this question and its answers point out, projecting a sphere on a flat picture plane, with perspective projection, may result in a ellipse, not a circle, and my understanding is that the only way a ...
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1 vote
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### how to change the near clipping plane of a perspective projection matrix for OpenGL

I am trying to only change the near clipping plane of a given perspective projection matrix for OpenGL. My problem is, that the near clipping plane is way too close, and the far clipping plane is very ...
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1 vote
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### What is this graphical effect called?

I was watching this trailer: https://www.youtube.com/watch?v=pWh5388AEHw and at 1:22, the player used a magic trick that created a sphere that warped the projection of the scene. Does anyone know ...
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102 views

### computing sheared perspective projection matrix

is it possible to calculate a "projection matrix" which is sheared as well? the usual perspective projection matrix forms a pyramid where the near clipping plane is rectangular. I have 4 ...
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1 vote
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### is focal length equal to the distance from the optical center to the near clipping plane- openGL

The part confusing about opengl during studying the projection was that the focal length, top, left, bottom, right, wasn't declared, and it magically did it with FOV and image aspect ration. I ...
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### Moving a vertex through the cursor

There is a way to move a selected point in a mesh with a cursor(assuming a camera that doesn;t change between frames). The way I remember the algorithm (but seems to be wrong) is: Unproject the ...
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1 vote
38 views

### Does angular diameter to FoV ratio equal object's image to total image ratio?

If we have an object at certain distance D in front of a camera. The object has a horizontal diameter d, giving us an angular diameter theta (2*arctan(d/2D)) of 50 degrees (converted from radians). ...
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### Project grid on 2d plane based on camera perspective

Unsure if this is the right network to post this, but maybe someone can help... I'm working on a personal project where, with the help of AI, I want to automatically estimate the perspective of a ...
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### What is the best way to calculate the projected size of a point

In a particle simulation, I am rendering particles as "spheres" using GL_POINTS instead of a mesh for efficiency. With glEnable(GL_PROGRAM_POINT_SIZE) I ...
1 vote
180 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 ...
41 views

### Can surface normal be used for obtaining points on a plane?

Excuse my wording. I will use the picture below to explain what I mean. I want to use the surface normals for each arrow shown like below to draw lines parallel to each plane like the image shown ...
1 vote
407 views

### How are textures projected onto 3d models in texture painting applications

In most modeling software you can texture paint onto 3d models using so called stencil textures. They basically project a texture from the viewport view onto the model as seen for instance in the ...
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### How is orthographic projection used in computer graphics technically classified as a projection?

I'm wondering why the orthographic projection we use in computer graphics is called a projection, if all it does is just scale and translate a mesh? According to wiki orthographic projection is ...
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### Perspective correct interpolation z-buffer

While I was deriving expressions for perspective-correct linear interpolation on triangles, I reached the conclusion that the interpolation may be kept linear only if view-space $Z$ is available. ...
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1 vote