Finding bearing from two points.

Posted on 2001-07-03
Last Modified: 2012-06-21

 Assume I have two points:

 p1 = x1, y1
 p2 = x2, y2

 I need to determine the DIRECTION/bearing (in degrees) of point p2 from point p1.  (The answer will of course be between 0 and 360).

 for example, if p1 = 0,0 and p2 = 5,5, it would be 45 degrees (Er, I think hehe).

Anyway, help is appreciated.  Psuedocode (java or c) would be helpful rather than just a bunch of theory.


Question by:Eltmon
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Accepted Solution

HDE226868 earned 300 total points
ID: 6251344
To calculate direction:

Starting point is p1
Ending point is p2
Angle is measured anticlockwise
0 degrees is straight right

Pseudocode example:

// First You calculate distances (must be in signed variables)


// If x part is 0 You could get into division by zero problems, but in that case result can only be 90 or 270:

if dx=0 {
   if dy > 0
     result = 90
     result = 270
else {

// otherwise angle is determined as inverse tangent of coordinates

   result = (atan(dy / dx)) * 180 / pi

// the *180 / pi part is because results are usualy in radians, but You wanted it in degrees

// this is only valid for two quadrants (for right side of the coordinate system) so modify result:

if dx < 0 {
   result = result + 180

// looks better if all numberes are positive (0 to 360 range)

if result < 0 {
   result = result + 360

Expert Comment

ID: 6251349
In c/c++ You can also use atan2 function, which should give it all without all that if sentences. But to understand, just go through the whole process as described before.

Author Comment

ID: 6251376
THANKS that worked PERFECTLY.... I was actually close but I had some misunderstandings that you cleared up.

Excellent job, THANKS!
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Author Comment

ID: 6251381
THANKS that worked PERFECTLY.... I was actually close but I had some misunderstandings that you cleared up.

Excellent job, THANKS!

Author Comment

ID: 6251382
How can I modify to use atan2 function?  

Expert Comment

ID: 6251408
double atan2( double y, double x );

I never used it before, but it seems it handles all that zero and quadrant handling. Should work like this:

result = (atan2(dy , dx)) * 180 / pi

if result < 0 {
  result = result + 360

From msdn:

atan returns the arctangent of x. atan2 returns the arctangent of y/x. If x is 0, atan returns 0. If both parameters of atan2 are 0, the function returns 0. You can modify error handling by using the _matherr routine. atan returns a value in the range ??/2 to ?/2 radians; atan2 returns a value in the range ?? to ? radians, using the signs of both parameters to determine the quadrant of the return value.

The atan function calculates the arctangent of x. atan2 calculates the arctangent of y/x. atan2 is well defined for every point other than the origin, even if x equals 0 and y does not equal 0.


Author Comment

ID: 6251422
Thanks once again!  I noticed in your bio that you work on game 3d stuff on the side.  I've been working on the same game for 5 years, and even have a Java3D client that is semi-working for it. It supports multiple types of play simultaneously, you can telnet to it like a mud, use a 3d client or 2d client, and its basically an MMRPG like asherons call or everquest.  Email me at if you are interested in learning more.

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Id love to hear from you,and thanks again!

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