Questions tagged [projections]

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

Filter by
Sorted by
Tagged with
0 votes
0 answers
11 views

Determine horizontal FOV of a panoramic photo

Say I have a panoramic photo (less than 360) and would like to view it in a cylindrical screen in a VR headset to get an immersive experience. How to determine the optimal width and height of the ...
Jack Guo's user avatar
3 votes
1 answer
39 views

Formula for cubemap resolution for intended equirectangular resolution

Suppose I want to render out 6 cubemap cameras (90 degree FOV etc.) with the intention of combining them together in post-production into an equirectangular (latlong, 2:1) image. Suppose I also know ...
kinkersnick's user avatar
0 votes
0 answers
19 views

How to extract points corresponding to faces from cube map projection (CMP) of panorama from point cloud data

I am working with the standford2d3d dataset http://buildingparser.stanford.edu/dataset.html which contains panoramas of various scenes and a .mat file of the point cloud information of all the scenes. ...
Miguel's user avatar
  • 1
0 votes
1 answer
17 views

viewing direction vectors are not parallel in orthographic projection

I did some math with orthographic projection matrix to compute viewing direction vectors in screen space. I thought all viewing direction vectors should be parallel in orthographic projection because, ...
slyx's user avatar
  • 103
0 votes
0 answers
30 views

Object appears in unintended parts of the screen when using manual WorldToScreenPoint

Hy guys I'm new to 3d graphics and i lack some Linear algebra knowledge. I tried to recreate Unity's worldToScreenPoint method with kotlin on android. I copied some code from their forum and wrote ...
Illidan's user avatar
0 votes
0 answers
33 views

3D engine projection distortions

I'm trying to write my own 3D engine using Python and Pygame. I have successfully implemented rotation and projection matrices to display 3D models. However I am so far unable to implement translation ...
Zoler1337's user avatar
1 vote
0 answers
88 views

Is it possible to render to a octahedron texture directly?

I am considering using octahedron textures for environment mapping, opposed to sphere or cube mapping due to their low memory footprint and the quality they result in. Is there a possibility to render ...
Raildex's user avatar
  • 173
0 votes
0 answers
125 views

Normalized Device Coordinates: Why normalize the Z value?

I understand that the normalized device coordinates are the result of the perspective divide of clip space coordinates and allow for an easy mapping of the xy coordinates to a physical screen. What I ...
Sam's user avatar
  • 164
0 votes
1 answer
68 views

What are applications of 3D geometry to 2D geometry projection and occlusion handling?

As a layperson in the field of computer graphics, I rarely see practical applications of algorithms that take 3D geometry as the input (along with some camera and lighting parameters) and output the ...
Max Flow's user avatar
  • 103
0 votes
1 answer
61 views

My projection matrix for OpenGL fails on non-symmetric boundaries

Assuming my viewing volume has x coordinates varies from l to r, and y varies from top to bottom, and finally z-axis varies n to f, I derived the following projection matrix: ...
Serilena's user avatar
2 votes
2 answers
246 views

How do I evenly subdivide the projection of a circle in 3D?

I want to draw a circle in 3D from line segments. There are plenty of examples how to do this with an even number of subdivisions in 3D space, but I want the minimum number of subdivisions to produce ...
user1387's user avatar
  • 121
1 vote
2 answers
323 views

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 ...
Makogan's user avatar
  • 1,706
0 votes
1 answer
51 views

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 ...
mardari's user avatar
0 votes
0 answers
76 views

Alternate projections in shader

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 ...
Roman's user avatar
  • 3
1 vote
1 answer
331 views

Why need glClipControl-like extensions when implementing ReverseZ in opgl?

I read this article (https://developer.nvidia.com/content/depth-precision-visualized) about reverseZ and I'm confused about why is glClipControl necessary.Can't we juse modify ProjectionMatrix to make ...
Grown's user avatar
  • 11
2 votes
0 answers
157 views

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 ...
Eduard Kovalets's user avatar
1 vote
3 answers
386 views

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 ...
MiguelP's user avatar
  • 111
1 vote
2 answers
426 views

mapping of a point from a sphere into UV plane

I am reading the book An introduction to raytracing by Eric Haines and it mentions an algorithm to map a point from a sphere into a UV plane, it calls it Inverse Spherical Mapping (page 49). I googled ...
Serilena's user avatar
0 votes
1 answer
503 views

Understanding orthographic projection matrix clip coordinates

I'm confused about what orthographic projection matrix outputs. Based on what I know so far, orthographic projection matrix converts vertexes in eye coordinates into clip coordinates. But what exactly ...
Jimmy Yang's user avatar
2 votes
1 answer
248 views

Is it possible to make a projection matrix to not project in the center?

I have the following projection matrix: and I need to make a hole in the center of my matrix, something like that: (I don't want to project a custom W and H) Is that possible ? Thanks.
Cosma Eduard's user avatar
1 vote
1 answer
71 views

What fields should a camera class have?

For a good and scalable project structure, what fields would you add to a camera class, apart from its position and orientation? Should I add the near and far planes? Or should that be global, what ...
Karlos's user avatar
  • 113
0 votes
1 answer
426 views

Where exactly is the image plane / plane of projection

Perspective projection matrices we use map 3D coords onto some imaginary image plane in front of the cameras pinhole position by casting a ray directly from the eye position to that 3d coordinate and ...
cg_guy420's user avatar
  • 115
4 votes
1 answer
856 views

How to derive Field of View (FOV) angles from a 2D projection

I'm looking for some guidance. I'm not sure if this is possible, and I'm not sure where to start. I need to measure the FOV angles of a first-person, 3D game using only gameplay screenshots. I'm bound ...
Brovidio's user avatar
0 votes
1 answer
338 views

Unity - custom shadow from sun

due to some features in materials I need to create my own directional shadow map. Everything seems to work ok, until the moment where I compare depths. First I add camera component to directional ...
Derag's user avatar
  • 596
2 votes
1 answer
79 views

When fitting 3d cuboids into a box, how to find the order of drawing (in a 2D projection) so that the cuboids don't appear to overlap?

I am working on a 3D packing algorithm (MIT-licensed). The box and the cuboids it contains are displayed as a 2D projection. The order of drawing the cuboids (now represented as polygons) is important:...
developer1405's user avatar
-1 votes
1 answer
168 views

Why we calculate z buffer value from plane equation $AX+BY+CZ+D=0$?

Suppose in perspective projection $(x, y, z)$ coordinate projects to point $(x_p, y_p, z_{vp})$ in projection plane $AX+BY+CZ+D=0$ where projection plane kept at $z_{vp}$ position. And the plane $AX+...
S. M.'s user avatar
  • 211
0 votes
1 answer
195 views

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 ...
Simon's user avatar
  • 183
2 votes
1 answer
384 views

3D homogenous coordinates versus 4D homogenous coordinates

We know that any 2D point $(x, y) $which represents as 3D homogeneous coordinates is of the form $(x, y, 1)$ which is the points of projective plane $P^2.$ If I use the same concepts for 3D points $(...
S. M.'s user avatar
  • 211
3 votes
2 answers
263 views

$(x, y, 1)$ is 2D homogenous coordinates or 3D homogenous coordinates?

We know that $(x, y, 1)$ are the homogenous coordinates of a 2D point $(x, y)$. $(x, y, 1)$ has 2 degrees of freedom. That's why we should call it 2D homogenous coordinates. But many websites say it's ...
S. M.'s user avatar
  • 211
2 votes
1 answer
106 views

Finding a texture pixel (X,Y) on a Sphere

I'm using three.js combined with face recognition, I want to rotate a sphere that displays my input video according to the detected eye location, the face recognition gives me a X,Y on the texture ...
nirhere's user avatar
  • 23
0 votes
1 answer
330 views

Perspective transformation is perspective projection? [duplicate]

I know that ( Reference )in transformation source and destination has same coordinates dimensions. But in projection destination coordinate system has fewer dimensions than the source coordinate ...
user avatar
1 vote
5 answers
2k views

Existence of vanishing point

Consider the following example of perspective projection: I have one railway track with two parallel lines meeting at the point $X$ at infinity which is the theoretical approach. This X is called the ...
user avatar
1 vote
0 answers
64 views

3D shearing w. r. t $x$-axis [closed]

Shearing in $X$ axis is achieved by using the following shearing equations- $X_{new} = X_{old}, Y_{new} = Y_{old} + Sh_y × X_{old}, Z_{new} = Z_{old} + Sh_z × X_{old}.$ My question is during $Y_{new}...
user avatar
3 votes
1 answer
785 views

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 ...
user avatar
2 votes
2 answers
281 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 ...
user avatar
3 votes
1 answer
874 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 $(x, y)$ ...
user avatar
1 vote
1 answer
84 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 ...
user avatar
1 vote
2 answers
269 views

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 ...
user avatar
1 vote
1 answer
1k views

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(...
user avatar
2 votes
1 answer
216 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 ...
user avatar
1 vote
0 answers
70 views

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 ...
Lenny White's user avatar
0 votes
1 answer
317 views

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 ...
Vun-Hugh Vaw's user avatar
1 vote
1 answer
591 views

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 ...
Thomas's user avatar
  • 1,265
1 vote
2 answers
163 views

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 ...
user1584421's user avatar
0 votes
0 answers
131 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 ...
Thomas's user avatar
  • 1,265
1 vote
1 answer
2k views

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 ...
juztcode's user avatar
  • 117
0 votes
1 answer
66 views

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 ...
Makogan's user avatar
  • 1,706
1 vote
1 answer
63 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). ...
Physician's user avatar
  • 115
4 votes
0 answers
168 views

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 ...
Chris's user avatar
  • 41
2 votes
0 answers
256 views

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 ...
user avatar