How can I calculate the angle between two 2D vectors?

Posted by Error 454 on Game Development See other posts from Game Development or by Error 454
Published on 2011-01-07T02:58:06Z Indexed on 2012/11/25 23:24 UTC
Read the original article Hit count: 172

Filed under:

2d

|

vector

I am working on some movement AI where there are no obstacles and movement is restricted to the XY plane. I am calculating two vectors, v, the facing direction of ship 1, and w, the vector pointing from the position of ship 1 to ship 2.

I am then calculating the angle between these two vectors using the formula

arccos((v · w) / (|v| · |w|))

The problem I'm having is that arccos only returns values between 0° and 180°. This makes it impossible to determine whether I should turn left or right to face the other ship.

Is there a better way to do this?

© Game Development or respective owner

Related posts about 2d

Are high powered 3D game engines better at 2D games than engines made for 2D

as seen on Game Development - Search for 'Game Development'
I'm a software engineer that's new to game programming so forgive me if this is a dumb question as I don't know that much about game engines. If I was building a 2D game am I better off going with an engine like Torque that looks like it's built for 2D, or would higher powered engines like Unreal… >>> More
2D Array of 2D Arrays (C# / XNA) [on hold]

as seen on Game Development - Search for 'Game Development'
I want to create a 2D array that contains many other 2D arrays. The problem is I'm not quite sure what I'm doing but this is the initialization code I have: int[,][,] chunk = new int[64, 64][32, 32]; For some reason Visual Studio doesn't like this and says that it's and 'invalid rank specifier'… >>> More
Need to know the origin and coordinates for 2d texture and 2d/3d vertices in webgl

as seen on Game Development - Search for 'Game Development'
Long story short, I know my coordinates are off and I believe my indices might be off. I'm trying to render a simple 2d rectangle with a texture in webgl here's the code I have for the vbo/ibo: rectVertices.vertices = new Float32Array( [ -0.5, -0.5, // Vertice 1, bottom / left 0.0, … >>> More
USB packets - receive wrong data

as seen on Ask Ubuntu - Search for 'Ask Ubuntu'
i have a little python script which shows me the packets of an enocean device and does some events depending on the packet type. unfortunately it doesn't work because i'm getting wrong packets. Parts of the python script (used pySerial): Blockquote ser = serial.Serial('/dev/ttyUSB1',57600… >>> More
Php 2d array as C# 2d array/struct

as seen on Stack Overflow - Search for 'Stack Overflow'
I'm using MailChimp's API to subscribe email to a list. Function listsubscribe() is used for email subscription: public static listSubscribe(string apikey, string id, string email_address, array merge_vars, string email_type, boolean double_optin, boolean update_existing, boolean replace_interests… >>> More

Related posts about vector

vector iterator not dereferencable at runtime on a vector<vector<vector<A*>*>*>

as seen on Stack Overflow - Search for 'Stack Overflow'
Hi, I have this destructor that create error at runtime "vector iterator not dereferencable". The gridMatrix is a std::vector<std::vector<std::vector<AtomsCell< Atom<T> * > * > * > * > I added the typename and also the typedef but I still have the error. I will move… >>> More
Adding Functions to an Implementation of Vector

as seen on Stack Overflow - Search for 'Stack Overflow'
I have this implementation of vector that I've been working on for a few days using examples from a textbook: #include <iostream> #include <string> #include <cassert> #include <algorithm> #include <cstring> // Vector.h using namespace std; template <class T> class… >>> More
Making only the outer vector in vector<vector<int>> fixed

as seen on Stack Overflow - Search for 'Stack Overflow'
I want to create a vector<vector<int>> where the outer vector is fixed (always containing the same vectors), but the inner vectors can be changed. For example: int n = 2; //decided at runtime assert(n>0); vector<vector<int>> outer(n); //outer vector contains n empty vectors outer… >>> More
(R) How can I get the complement of vector y in vector x

as seen on Stack Overflow - Search for 'Stack Overflow'
That's x \ y using mathematical notation. Suppose x <- c(0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,1,1,2,1,1,1,3) y <- c(0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,1,1,1) How can I get a vector with ALL the values in x that are not in y. i.e the result should be: 2,1,1,3 There is a similar question here… >>> More
C++: Appending a vector to a vector

as seen on Stack Overflow - Search for 'Stack Overflow'
Assuming I have 2 STL vectors: vector<int> a; vector<int> b; Let's also say the both have around 30 elements. How do I add the vector b to the end of vector a? The dirty way would be iterating through b and adding each element via push_back, though I wouldn't like to do that! >>> More