# Questions tagged [geometry]

A branch of mathematics concerned with questions of shape, size, relative position of figures, and the properties of space.

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### How does a 4x4 matrix represent an object in space and matrix lore?

I have been following some tutorials on how Matrix maths works, with adding, dividing, scaling, etc, but I am struggling to understand how the 4x4 matrix represents an object's position in space. ...
1answer
1k views

### Formula to measure uv-mapping distortion

Does anyone know a simple way of calculating (offline) the amount a texture is distorted when mapped to a triangle like the following? ...
1answer
77 views

### How can I detect whether a point is moving in a circle?

I want to detect if my GameObject (Vector3 Point) being dragged by the player's finger is moving in a circular fashion. I thought I could save the last 5 points ...
1answer
19 views

### Find optimal placement for label/sticker on a simple polygon with holes

I'm working on a real-time archviz renderer and I need to place a label/sticker/decal on walls, which have openings. So one way to think about this is a simple (possibly concave) polygon with holes. ...
1answer
399 views

### Overlap color between objects

I'm currently trying to build a game with Ogre3D that is basically a moving vehicle that leaves a green trail (2D manual mesh) in it's path, what i'm trying to achieve is exactly what this image shows:...
2answers
102 views

### How do I launch a ballistic projectile to hit a moving target, given: launch position & angle, target position & velocity?

This problem is in 3D space. My question is: How do you find the initial velocity of a projectile that flies under constant gravity, so that it hits a target moving with constant velocity, given the ...
1answer
217 views

### Background made with procedural shapes

I would like to know how to make a background like Super Hexagon managed to do: a hexagon in the middle and equally sized trapezoids. There's a screenshot below & the here is the effect in motion....
0answers
17 views

### Correct primitive to start with for modified cone shape

I am very new to Maya and trying to make a Nikon F camera from reference images. I can't quite wrap my head around how I would make the shape on top of the camera because it is essentially a square ...
2answers
54 views

### Detect walls in geometry

Is it possible to automatically detect walls in polygon soup? Of course it's hard to strictly define what a wall is, my slightly vague definition would be: A wall is a largest possible box (not ...
2answers
10k views

### How do I find the circumcenter of a triangle in 3D?

I want to find the circumcenter of a triangle. Wolfram only shows how to find the circumcircle of a triangle in R2. How can I find the circumcenter of a triangle in R3?
0answers
30 views

### Generation of a 3D loop the loop with minimal steering required

How would I generate a surface which resembles a loop-the-loop shape like this one described here? After triangulation of the surface, lets say I start at one end with some initial velocity which is ...
1answer
50 views

### How to know if two surface are in the same direction?

In my code I creat a Mesh that are composed by multiple tile. those tile can have edge that are shared, and I need to know if the normal of the tile that have shared edge have the same direction, ...
1answer
45 views

### Calculating approximations of contact between two meshes

I'm looking for ways to calculate the degree of contact between two objects in a scene. I was thinking that calculating the hausdorff distance would be a useful approximation if it is then normalized ...
3answers
12k views

### How to move an object along a vector

Let's say I got an object A and object B in a 2D game. I create a vector leading from A to <...
3answers
176 views

### Get closest point on box to line

Eventually this problem will be 3D, so I would like a solution that works in 3D. My player is looking forwards. There is an axis-aligned box on the screen (FOV is guaranteed to be 90, so boxes behind ...
1answer
50 views

### Push cube outside triangle face

I'm creating a 3D game, and I need to know how to push a player (axis aligned box/cube) outside a triangle. How can I get get the push direction?
1answer
243 views

### Convert 3D direction vectors to yaw/pitch/roll angles

I have the code below that takes a set of yaw, pitch, and roll rotation angles (in degrees), and populates forward, right, and up basis vectors to express this rotated orientation as a Cartesian ...
1answer
87 views

### Click on an isometric plane and obtain normal coordinates

I have photos distributed as cells. When I click, I get the corresponding row and column. console.log("Col:" + X + "Row:" + Y); When applying an isometric view conversion like this: ctx.translate(0, ...
1answer
53 views

### How can I build an array of coordinates of a truncated icosahedron's faces?

I can easily get a list of coordinates of all the vertices—the Wikipedia page has formulae and this page has a list of them, but that doesn't tell me which ones are part of which face. What I'd like ...
0answers
16 views

### Moving and rotating object with another object [duplicate]

Sorry i bad painter)) Need move and rotate 'OBJECT №2' with 'OBJECT №1' I have origin point(also rotation point) and angles of two object. (Also min and max coordinates of these objects) Vector ...
1answer
79 views

### Move and rotate one object to another C++ [3D]

I have two object, need attach 'TWO OBJECT' to 'ONE OBJECT'. I have vectors 'angle' 'origin' of ONE and TWO objects. I tried do "TWOOBJECT.origin += ONE.origin - ONE.oldorigin", this just attach ...
1answer
71 views

### How to detect least distance to line segments calculation

I'm trying to calculate the distance of the player to a few lines that intersect two points, and return the smallest distance (i.e. tell me which of the lines the player is closest to/how far the ...
2answers
286 views

### Rotate perspective camera to align screen width to procedural object's width (Unity, C#)

I give up. After much trying and searching, I have to say I was unable to achieve the following task, for which I must call for your wise advice. In my current Unity 5 application (using C#), there ...
2answers
1k views

### How to rotate a local position offset based on a direction vector?

I'm trying to fire three raycasts in the direction of movement, from offset starting points. I'm having trouble calculating the start positions of the rays based on the direction. As you can see in ...
2answers
277 views

### Shrink a convex polygon

Shrinking a concave polygon is quite hard, to do well. But I expect shrinking a convex polygon would be easy. The naive approach of moving each vertex a certain distance to the centre gives me poor ...
1answer
19 views

### Get the mesh Project Plane on Click and calculate its area

Here is the excerpt of my script which is calculating the surface area and face area of a mesh on OnMouseDown Event. ...
1answer
86 views

### Get triangles after subdivision

I was able to do subdivision on a triangle mesh with midpoints but then I get polygons with too many faces. How do I convert to triangles after? Similar to this picture:
2answers
358 views

### which quarter of a triangle the point is in

I've got a world made out of squares. The square are devided in four triangles like this: The corners have their heights stored in a 2D array and the center height is the average of the corners. To ...
2answers
230 views

### Most efficient way to get the closest point to a 3d rectangle

I have a 3D rectangle, with 4 points (x,y,z) And I have a player, who can be anywere (inside the rectangle, outside, not even in the plane, in the corner...). I would like to get the closest point in ...
0answers
62 views

### algorithm to change the center of the image

I need and algorithm in Java if possible to change the center of the image when scaling.What is happening to me is represented in the first image: when I scale the image the image scale according to ...
2answers
44 views

### Unity3D - Generate a position within a circular band around the player

Given a certain condition in my game I need to generate a position around the player. It needs to be at least 8 meters away from him and within 10 meters, in a circular matter, as in the dotted green ...
0answers
10 views

### Object's plane on image

I have a segmented image. So, for example, I know 2D coordinates of pixels for road on image. Now I want to know a plane of this road. How can I do this? P.S. I think it's popular problem, so I'm ...
1answer
41 views

### Calculating surface normal numerically

Say I have a 2D surface defined with the use of bitmap. I want to use this bitmap for collision detection (white color is where object can move freely, with black I mark the walls). How can I ...
2answers
486 views

### Getting the bounding box of a sphere

I have a sphere with values center,radius and I need to convert the sphere to a bounding box with values min,max. How do I ...
1answer
72 views

### Get a Jump normal gravity based on Attractor Points, lines or Quad placed in the Level Design (in a Mario galaxy like gravity)

I have an algorithme to find. I have a player in a 3D space on a random planet. My goal is to have an oriented gravity toward my planet. And when I jump: Find the right normal direction. BUT I can't ...
0answers
60 views

### Getting the Closet Points between Polygons with the GJK Algorithm

I am trying to implement the GJK algorithm by following this lecture. For the most part, it is working, but sometimes 1 of the 2 closest points is incorrect. Here are two examples: EXAMPLE 1: The ...
0answers
126 views

### Find transformation to align two polygons at fixed points?

Problem I have a source image (arbitrary width and height c) shown here as a rectangle [X1,X2,X3,X4]. It contains two points C and D (both known coordinates within ...
1answer
78 views

### How to determine polygon based on point lists?

I have several lists of interconnected points. They are ordered so I can connect them together. Using these interconnected points I'd like to find the different points and intersection points that ...
0answers
21 views

### Is it possible to generate a 2D surface that approaches certain mesh, and then a specialised ray-tracing function for it?

As an example, suppose we are trying to ray-trace a sphere. There are two options. The first one is to build a mesh of triangles approximating the sphere and ray trace it. Unfortunately, the more ...
3answers
326 views

### exact point on a rotating sphere

I have a sphere that represents the Earth textured with real pictures. It's rotating around the x axis, and when user click down it has to show me the exact place he clicked on. For example if he ...
1answer
40 views

### Interpreting focal length in units of pixels

I am working on a renderer of sorts and I have some fundamental questions. Let's say I have a vector in a 3D virtual world space which is unitless, and I want to project it onto a 2D screen, so I need ...
2answers
968 views

### How can I mask this CanvasRenderer?

I'm creating a text box that allows for selectable text, based off of Unity's InputField. An issue I am now facing is that the selection highlight does not respond to masks (The parent has a mask, but ...
3answers
107 views

### How can you tell if you are a large player on a large map or a small player on a small map?

If everything is scaled by a constant factor, can you tell that the world is smaller or larger? I think you could look down at the ground and see that it's "closer". But how do you know what ...
1answer
52 views

### How to implement level-player collisions resolution?

I want to create simple collision response system (physical simulation is not required now). It is needed just that player can't go through walls. I consider some variants: - Just create a set of ...
1answer
1k views

### How to calculate the surface area of a mesh

I am looking for a way to calculate surface area of a 3D mesh object and found this code from a Unity forum: ...
1answer
81 views

### How can I express Logarithmic and Arithmetic spirals as segmented cubic bezier curves?

I am creating cubic bezier curves using this code from another question I asked. I would like to know how I can express Logarithmic and Arithmetic spirals as segmented cubic bezier curves.
1answer
71 views

### How to inflate geometry?

I have a shape containing vertices and triangles I want to inflate that geometry using some radius to get something like that I should move each point along ...
1answer
8k views

### How do you turn a cube into a sphere?

I'm trying to make a quad sphere based on an article, which shows results like this: I can generate a cube correctly: But when I convert all the points according to this formula (from the page ...
1answer
463 views

### Why are spherical worlds so rare?

I remember back in the 90s when X-Com came out, being really impressed by the way its world map was an actual world: a map of Earth drawn on a spherical surface. That was pretty cool, because I had ...
1answer
93 views

### Confused by scaling, units, and more

Ok, so I've already waded through a bunch of questions around this, and it's just making me even more confused. Let's say I am trying to model a card table in a 2d game. Behind (beneath) the table ...