Angle difference between two bearings

How do I find the minimum angle difference between two angles A & B, for example:

if A = -175, B = 175 -> difference would be 10

if A = 355, B = 5 -> difference would be 10

if A = 720, B = 360 -> difference would be 0

etc.

All I know is that I have to use the absolute and modulus functions somewhere

Would appreciate any help.

Answer 1

[Basil C.]

Read about principal angles...

For the 1st case:

A=-175 whose principal angle is 185 degree

A - B = 185 - 175 = 10 degrees

You can similarly solve the for the remaining cases

[Shikhar Singh]

Here is how they've done it in java:

public static double getDifference(double b1, double b2) {

double r = (b2 - b1) % 360.0;

if (r < -180.0)

r += 360.0;

if (r >= 180.0)

r -= 360.0;

return r;

}

System.out.println("Input in -180 to +180 range");

System.out.println(getDifference(20.0, 45.0));

I was wondering if something similar could be done on matlab

[Basil C.]

The problem with your code is that it A and B must be in the principal form for the code to work.

To solve your question, A and B need to be converted to the principal angle and then just subtract them

[Shikhar Singh]

How would this work for an angle like 1060 then?

Answer 2

[Basil C.]

To convert any angle to its principal angle

function y = prin_angle(x)
    y=rem(x,360); % returns the remainder when dividing by 360
    if y<0
        y=y+360;
    end
end

Just pass both angles to above function individually to obtain the principal angle, then subtract the two outputs

OR

Just use the following code and pass both A and B directly:

function y = get_difference(A,B)
    y=rem(B-A,360); % returns the remainder when dividing by 360
    if y<-180
        y=y+360;
    elseif y>180
        y=y-360;
    end
end

P.S.: I have just converted the java code from above into matlab code

[Shikhar Singh]

Hey,

Thanks for converting the java code to matlab above, it works great, however there's one error that's coming up, when I input:

get_difference(-175,175) it returns -10

but when I input

get_difference(175,-175) it returns 10

I'd like for it to return 10 in both cases, how can i fix that, so that this problem doesn't occur in other cases?

[Basil C.]

function y = get_difference(A,B)
    y=rem(B-A,360); % returns the remainder when dividing by 360
    if y<-180
        y=y+360;
    elseif y>180
        y=y-360;
    end
    y=abs(y)
end

[Shikhar Singh]

That works perfectly now, thanks a lot!

[darova]

[cem polat]

Use anglediff function in Communications or Robotics toolbox. Since anglediff uses radians, you can use a function like below for the angle diff in degrees:

function result = angdiffdeg(from, to)

result = rad2deg(angdiff(deg2rad(from),deg2rad(to)));

end