Calculate angle between two points ??

[NewOnJava]

Hello!

I have the following code to calculate the angle between two 2D points ->

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public float calcAngle ( Point p1 , Point p2 )     {         float fx = (float)(p2.getX()-p1.getX());         float fy = (float)(p2.getY()-p1.getY());         float f1 = 0f;                         if ( fx >= 0 ) if ( fy <= 0 ) f1 = (float)-Math.toDegrees(Math.atan(fx/fy));         if ( fx >= 0 ) if ( fy >= 0 ) f1 = 90-(float)Math.toDegrees(Math.atan(fx/fy))+90;         if ( fx <= 0 ) if ( fy <= 0 ) f1 = 90-(float)Math.toDegrees(Math.atan(fx/fy))+270;         if ( fx <= 0 ) if ( fy >= 0 ) f1 = 90-(float)Math.toDegrees(Math.atan(fx/fy))+90;                         return f1;     }

My code is working all right, but, still i feel that it is a bit too complicated to be shown to other coders
How with Java i can make my code shorter and faster ??

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Thanks..

[Bonbon-Chan]

"The angle between two points" doesn't mean anything.
For the angle between two vectors (dx1,dy1) and (dx2,dy2), just use :
 Math.toDegrees(Math.atan2(dy1,dx1)-Math.atan2(dy2,dx2))

No ?

[Karmington]

this is 'calculate angle of one line' in effect.

Games published by our own members! Go get 'em!

[Roquen]

I think this is what you want:

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public static final float calcAngle(Point p0, Point p1)   {     float x0 = (float)p0.getX();     float y0 = (float)p0.getY();     float x1 = (float)p1.getX();     float y1 = (float)p1.getY();         // op = m sin(theta)    // ip = m cos(theta), where m = |P0| * |P1|    float op = x1*y0-x0*y1;     float ip = x0*x1+y0*y1;       return (float)Math.toDegrees(Math.atan2(op,ip));   }

But I'm not sure.  Your code returns 45 for: (0,1) & (1,0)  and something near 90 for (0,1) & (10000,0).  So I might be not understanding the question.

[dishmoth]

If you're after the angle of the line that passes through points p1 and p2, then

1	Math.toDegrees( Math.atan2( p2.getY()-p1.getY(), p2.getX()-p1.getX() ) )

should do it.

The result will be in the range -180 to +180 degrees, measured anti-clockwise from East (see the comments here on angles in polar coordinates).

Simon

[Eli Delventhal]

Yup, that's exactly what atan2 is for. You don't have to bother with checking quadrants like you've been doing.

[NewOnJava]

If you're after the angle of the line that passes through points p1 and p2, then

1	Math.toDegrees( Math.atan2( p2.getY()-p1.getY(), p2.getX()-p1.getX() ) )

should do it.

The result will be in the range -180 to +180 degrees, measured anti-clockwise from East (see the comments here on angles in polar coordinates).

Simon

Angle!

Ok, i get this example working on my plane game, i receive East -180 to East +180 degrees, still,
im after North +0 to North +360 degrees at on my game, is there any matematical solution with Java for North 0 to North 360 angles.

or, do i do tricks, like a i did on my first post ??

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Thanks..

[Eli Delventhal]

Angle!

Ok, i get this example working on my plane game, i receive East -180 to East +180 degrees, still,
im after North +0 to North +360 degrees at on my game, is there any matematical solution with Java for North 0 to North 360 angles.

or, do i do tricks, like a i did on my first post ??

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Thanks..

The result above makes East = 0.
If you want North to be 0, East effectively becomes -90.
That means, add 90 to the value returned.

The result above gives you a value from -180 to 180 (where 0 is east).
If you want to make it 0 to 360, effectively everything is 180 more.
That means, add 180 to the value returned.

We want to do both.

Let's convert it into an equation.

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public double convertToNorth(double angle) {     return angle + 90; } public double convertTo360(double angle) {     return angle + 180; }

Doing both means you've got to convert it to 360 and then make sure 0 is considered north. That means:

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public double doBoth(double angle) {     //At this point, -180 to 180 and East is 0.     angle = convertTo360(angle);     //At this point, 0 to 360 and West is 0.         angle = convertToNorth(angle);     //Now, 0 to 360 and North is 0.     return angle; }

Make sense yet? What's the final result? That's right. Add 270.

 

[NewOnJava]

calcAngle!

Here is my final function, it is now lot shorter and maybe a lot faster ->

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public float calcAngle (Point p1, Point p2 ) {     float f1 = (float)Math.toDegrees( Math.atan2( p1.getY()-p2.getY(), p1.getX()-p2.getX() ) );     f1+=270;     while ( f1 > 360 ) f1-=360;     while ( f1 <   0 ) f1+=360;     return f1; }

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Thanks..

[Riven]

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public float calcAngle (Point p1, Point p2 ) {     float f1 = (float)Math.toDegrees( Math.atan2( p1.getY()-p2.getY(), p1.getX()-p2.getX() ) );     return (f1+270)%360; }

Games published by our own members! Go get 'em!

[Markus_Persson]

Do you need to know the angle?

I often find that it's both faster and easier to work with vectors and dot products.

[Eli Delventhal]

Do you need to know the angle?

I often find that it's both faster and easier to work with vectors and dot products.

One time I needed the angle specifically for where I was applying a rotation to Sprite (a goal compass). Otherwise I've always used vectors.

[imorio]

Make sense yet? What's the final result? That's right. Add 270.

I know I'm replying to an old post but this answer is just wrong I think.

The original results would give if:
north=90
west=180 or -180
south= -90
east= 0

adding 270 gives:

north=360
west=450 or 90
south=180
east=270

the only result I can think of that would be usefull is:

north=0 or 360
east or west=270
south=180
east or west=90

edit: This gives the right answer if the original answer was "polar":
int nonPolar= 90-((polar+180)%360)
if(nonPolar<0)
{
nonPolar=nonPolar+360;
}