Questions tagged [geometry]
Data structures and algorithms related to geometry.
geometry
13,125
questions
2029
votes
23
answers
250k
views
How do CSS triangles work?
There're plenty of different CSS shapes over at CSS Tricks - Shapes of CSS and I'm particularly puzzled with a triangle:
#triangle-up {
width: 0;
height: 0;
border-left: 50px solid ...
- 19.2k
515
votes
27
answers
591k
views
How do you detect where two line segments intersect? [closed]
How do I determine whether or not two lines intersect, and if they do, at what x,y point?
- 66.8k
448
votes
56
answers
352k
views
Shortest distance between a point and a line segment
I need a basic function to find the shortest distance between a point and a line segment. Feel free to write the solution in any language you want; I can translate it into what I'm using (Javascript)....
438
votes
32
answers
541k
views
Calculate distance between 2 GPS coordinates
How do I calculate distance between two GPS coordinates (using latitude and longitude)?
- 7,189
407
votes
21
answers
349k
views
Determine if two rectangles overlap each other?
I am trying to write a C++ program that takes the following inputs from the user to construct rectangles (between 2 and 5): height, width, x-pos, y-pos. All of these rectangles will exist parallel to ...
- 5,435
399
votes
17
answers
371k
views
Equation for testing if a point is inside a circle
If you have a circle with center (center_x, center_y) and radius radius, how do you test if a given point with coordinates (x, y) is inside the circle?
directedition
341
votes
25
answers
374k
views
How to determine if a point is in a 2D triangle? [closed]
What is the simplest algorithm to determine if a point is inside a 2d triangle?
- 3,493
337
votes
25
answers
200k
views
How to determine if a list of polygon points are in clockwise order?
Having a list of points, how do I find if they are in clockwise order?
For example:
point[0] = (5,0)
point[1] = (6,4)
point[2] = (4,5)
point[3] = (1,5)
point[4] = (1,0)
would say that it is anti-...
- 12.2k
308
votes
23
answers
251k
views
Generate a random point within a circle (uniformly)
I need to generate a uniformly random point within a circle of radius R.
I realize that by just picking a uniformly random angle in the interval [0 ... 2π), and uniformly random radius in the ...
- 417k
265
votes
6
answers
461k
views
How to do a scatter plot with empty circles in Python?
In Python, with Matplotlib, how can a scatter plot with empty circles be plotted? The goal is to draw empty circles around some of the colored disks already plotted by scatter(), so as to highlight ...
- 92.9k
244
votes
27
answers
268k
views
Circle-Rectangle collision detection (intersection)
How can I tell whether a circle and a rectangle intersect in 2D Euclidean space? (i.e. classic 2D geometry)
- 46.2k
243
votes
15
answers
117k
views
An algorithm for inflating/deflating (offsetting, buffering) polygons
How would I "inflate" a polygon? That is, I want to do something similar to this:
The requirement is that the new (inflated) polygon's edges/points are all at the same constant distance ...
- 18.8k
236
votes
6
answers
304k
views
Using the "animated circle" in an ImageView while loading stuff
I am currently using in my application a listview that need maybe one second to be displayed.
What I currently do is using the @id/android:empty property of the listview to create a "loading" text.
...
- 39.5k
225
votes
29
answers
188k
views
Circle line-segment collision detection algorithm?
I have a line from A to B and a circle positioned at C with the radius R.
What is a good algorithm to use to check whether the line intersects the circle? And at what coordinate along the circles ...
- 51.7k
213
votes
4
answers
259k
views
How do I calculate the normal vector of a line segment? [closed]
Suppose I have a line segment going from (x1,y1) to (x2,y2). How do I calculate the normal vector perpendicular to the line?
I can find lots of stuff about doing this for planes in 3D, but no 2D ...
- 3,576
205
votes
15
answers
467k
views
Easier way to create circle div than using an image?
I'm wondering if there's an easier way to create circular divs than what I'm doing now.
Currently, I am just making an image for each different size, but it's annoying to do this.
Is there anyway ...
- 2,303
204
votes
2
answers
7k
views
Why are my balls disappearing? [closed]
Pardon the funny title. I've created a little graphic demo of 200 balls bouncing and colliding, both against the walls and each other. You can see what I have currently here: http://www.exeneva.com/...
- 2,029
199
votes
18
answers
164k
views
Evenly distributing n points on a sphere
I need an algorithm that can give me positions around a sphere for N points (less than 20, probably) that vaguely spreads them out. There's no need for "perfection", but I just need it so none of them ...
- 6,650
198
votes
11
answers
157k
views
How can I find the smallest difference between two angles around a point?
Given a 2D circle with 2 angles in the range -PI -> PI around a coordinate, what is the value of the smallest angle between them?
Taking into account that the difference between PI and -PI is not 2 ...
- 9,821
188
votes
9
answers
116k
views
Sort points in clockwise order?
Given an array of x,y points, how do I sort the points of this array in clockwise order (around their overall average center point)? My goal is to pass the points to a line-creation function to end up ...
- 9,018
185
votes
12
answers
189k
views
Circle drawing with SVG's arc path
Using SVG path, we can draw 99.99% of a circle and it shows up, but when it is 99.99999999% of a circle, then the circle won't show up. How can it be fixed?
The following SVG path can draw 99.99% of a ...
183
votes
16
answers
211k
views
How to tell whether a point is to the right or left side of a line
I have a set of points. I want to separate them into 2 distinct sets. To do this, I choose two points (a and b) and draw an imaginary line between them. Now I want to have all points that are left ...
- 4,638
171
votes
31
answers
116k
views
How do you calculate the average of a set of circular data?
I want to calculate the average of a set of circular data. For example, I might have several samples from the reading of a compass. The problem of course is how to deal with the wraparound. The same ...
- 43.6k
165
votes
26
answers
242k
views
How can I check if two segments intersect?
How can I check if 2 segments intersect?
I've the following data:
Segment1 [ {x1,y1}, {x2,y2} ]
Segment2 [ {x1,y1}, {x2,y2} ]
I need to write a small algorithm in Python to detect if the 2 lines ...
- 63.9k
152
votes
6
answers
204k
views
Simple calculations for working with lat/lon and km distance?
Is there a simple calculation I can do which will convert km into a value which I can add to a lat or lon float to calculate a bounding box for searches? It doesn't need to be completely accurate.
...
- 19.1k
148
votes
20
answers
102k
views
Algorithm to detect intersection of two rectangles?
I'm looking for an algorithm to detect if two rectangles intersect (one at an arbitrary angle, the other with only vertical/horizontal lines).
Testing if a corner of one is in the other ALMOST works. ...
- 5,764
145
votes
10
answers
108k
views
How to create circle with Bézier curves?
We have a start point (x, y) and a circle radius. There also exists an engine that can create a path from Bézier curve points.
How can I create a circle using Bézier curves?
- 65.9k
140
votes
19
answers
363k
views
How to draw circle in html page?
How do you draw a circle using HTML5 and CSS3?
Is it also possible to put text inside?
- 26k
139
votes
14
answers
132k
views
Postgis installation: type "geometry" does not exist
I am trying to create table with Postgis. I do it by this page. But when I import postgis.sql file, I get a lot of errors:
ERROR: type "geometry" does not exist
Does anybody know how can I fix it?
- 2,396
133
votes
10
answers
370k
views
Converting from longitude\latitude to Cartesian coordinates
I have some earth-centered coordinate points given as latitude and longitude (WGS-84).
How can i convert them to Cartesian coordinates (x,y,z) with the origin at the center of the earth?
- 9,460
125
votes
21
answers
171k
views
How can you determine a point is between two other points on a line segment?
Let's say you have a two dimensional plane with 2 points (called a and b) on it represented by an x integer and a y integer for each point.
How can you determine if another point c is on the line ...
- 20.3k
120
votes
16
answers
291k
views
How to calculate an angle from three points? [closed]
Lets say you have this:
P1 = (x=2, y=50)
P2 = (x=9, y=40)
P3 = (x=5, y=20)
Assume that P1 is the center point of a circle. It is always the same.
I want the angle that is made up by P2 and P3, or in ...
HelloMoon
117
votes
15
answers
32k
views
Combined area of overlapping circles
I recently came across a problem where I had four circles (midpoints and radius) and had to calculate the area of the union of these circles.
Example image:
For two circles it's quite easy,
I can ...
- 2,161
114
votes
6
answers
74k
views
Animate drawing of a circle
I'm looking for a way to animate the drawing of a circle. I have been able to create the circle, but it draws it all together.
Here is my CircleView class:
import UIKit
class CircleView: UIView {
...
- 5,816
114
votes
8
answers
84k
views
Good geometry library in python? [closed]
I am looking for a good and well developed library for geometrical manipulations and evaluations in python, like:
evaluate the intersection between two lines in 2D and 3D (if present)
evaluate the ...
- 141k
106
votes
15
answers
93k
views
How do I calculate the area of a 2d polygon? [duplicate]
Assuming a series of points in 2d space that do not self-intersect, what is an efficient method of determining the area of the resulting polygon?
As a side note, this is not homework and I am not ...
- 13.3k
105
votes
9
answers
106k
views
Find the point on a circle with given center point, radius, and degree
It's been 10 years since I did any math like this... I am programming a game in 2D and moving a player around. As I move the player around I am trying to calculate the point on a circle 200 pixels ...
- 1,860
104
votes
13
answers
143k
views
Calculating the position of points in a circle
I'm having a bit of a mind blank on this at the moment.
I've got a problem where I need to calculate the position of points around a central point, assuming they're all equidistant from the center and ...
- 1,051
101
votes
11
answers
113k
views
Transparent circle with border
I am trying to create a circle with only a border using XML in android:
<?xml version="1.0" encoding="utf-8"?>
<shape xmlns:android="http://schemas.android.com/apk/res/android"
android:shape=...
- 2,080
99
votes
3
answers
170k
views
Plotting a 3d cube, a sphere and a vector
I search how to plot something with less instruction as possible with Matplotlib but I don't find any help for this in the documentation.
I want to plot the following things:
a wireframe cube ...
- 58.9k
99
votes
10
answers
166k
views
Finding whether a point lies inside a rectangle or not
I want to find whether a point lies inside a rectangle or not. The rectangle can be oriented in any way, and need not be axis aligned.
One method I could think of was to rotate the rectangle and ...
- 14.2k
98
votes
6
answers
283k
views
Draw radius around a point in Google map
I'm using the Google Maps API and have added markers. Now I want to add a 10 mile radius around each marker, meaning a circle that behaves appropriately while zooming. I have no idea how to do that ...
- 6,971
96
votes
11
answers
62k
views
How do I combine complex polygons?
Given two polygons:
POLYGON((1 0, 1 8, 6 4, 1 0))
POLYGON((4 1, 3 5, 4 9, 9 5, 4 1),(4 5, 5 7, 6 7, 4 4, 4 5))
How can I calculate the union (combined polygon)?
Dave's example uses SQL server to ...
- 31.8k
91
votes
11
answers
237k
views
How do I compute the intersection point of two lines?
I have two lines that intersect at a point. I know the endpoints of the two lines. How do I compute the intersection point in Python?
# Given these endpoints
#line 1
A = [X, Y]
B = [X, Y]
#line 2
...
- 2,023
88
votes
6
answers
27k
views
Position of the sun given time of day, latitude and longitude
This question has been asked before a little over three years ago. There was an answer given, however I've found a glitch in the solution.
Code below is in R. I've ported it to another language, ...
- 3,789
87
votes
10
answers
168k
views
Using atan2 to find angle between two vectors
I understand that:
atan2(vector.y, vector.x) = the angle between the vector and the X axis.
But I wanted to know how to get the angle between two vectors using atan2. So I came across this solution:
...
- 1,931
85
votes
10
answers
116k
views
Drawing Sphere in OpenGL without using gluSphere()?
Are there any tutorials out there that explain how I can draw a sphere in OpenGL without having to use gluSphere()?
Many of the 3D tutorials for OpenGL are just on cubes. I have searched but most of ...
- 15.3k
84
votes
2
answers
27k
views
Algorithm for finding the fewest rectangles to cover a set of rectangles without overlapping
I have a set of rectangles and I would like to "reduce" the set so I have the fewest number of rectangles to describe the same area as the original set. If possible, I would like it to also be fast, ...
- 3,666
83
votes
10
answers
102k
views
Signed angle between two 3D vectors with same origin within the same plane
What I need is a signed angle of rotation between two vectors Va and Vb lying within the same 3D plane and having the same origin knowing that:
The plane contatining both vectors is an arbitrary and ...
83
votes
12
answers
94k
views
Calculate Bounding box coordinates from a rotated rectangle
I have the coordinates of the top left point of a rectangle as well as its width, height and rotation from 0 to 180 and -0 to -180.
I am trying to get the bounding coordinates of the actual box ...
- 3,338