Java innacurate in calulating my angle?

Question

I am having a user draw a line on the screen, there is a start point and a end point. If the user extends over a certain angle I change the position of the endpoint so the user cannot extend beyond the specified angle. However it seems that when I cacluate the angle the user is drawing and make suer it is not over MAX ANGLE, and set the angle to the MAX ANGLE, there is a difference. This can be seen by when I draw the line, once i get to a certain angle, the line jumps and locks at the MAX ANGLE, but there shouldnt be any jump, it should be smooth, like the line ran into a invisible barrier. This could just be me though, my PosX and PosY are floats.

    private void CheckAngle() {
    double adj = Math.abs(PosX - PosX2);
    double c1 = adj;
    double c2 = Math.abs(PosY - PosY2);
    double hyp = Math.hypot(c1, c2);


    double angle = Math.cos((adj/hyp));
    angle = angle * 100;


    if (angle > MAX_ANGLE) {


        double opp = (Math.tan(MAX_ANGLE) * Math.abs(PosX - PosX2));


        if (PosY > PosY2) {
            PosY2 =(float) (PosY - opp);
        } else {
            PosY2 =(float) (PosY + opp);
        }

    }
}

My answer was a combination of using radians, as well as unsing

    Math.acos() & Math.atan()

so the final code looks like this

    private void CheckAngle() {
    double adj = Math.abs(PosX - PosX2);
    double opp = Math.abs(PosY - PosY2);
    double hyp = Math.sqrt((adj*adj)+(opp*opp));


    double angle = Math.acos((adj/hyp));
    angle = angle * 100;
    angle = Math.toRadians(angle);

    if (angle > MAX_ANGLE) {


        opp = (Math.atan(MAX_ANGLE) * adj);


        if (PosY > PosY2) {
            PosY2 =(float) (PosY - opp);
        } else {
            PosY2 =(float) (PosY + opp);
        }

    }
}

@Mysticial beat me to it: is MAX_ANGLE in degrees? Remember, all the Java trig functions work in radians. — Matt Ball
– Matt Ball, Commented Aug 4, 2012 at 0:00
I am not, not familliar with radians. Ha im taking trig this semester, geez, and people told me i was wasting time taking trig — WIllJBD
– WIllJBD, Commented Aug 4, 2012 at 0:03
To convert degrees to radians, multiply the number of degrees by pi/180. — jrad
– jrad, Commented Aug 4, 2012 at 0:04
if one of you guys posts an actual answer of how to convert say "final double MAX_ANGLE = (80*(pi/180)) I'll accept it. — WIllJBD
– WIllJBD, Commented Aug 4, 2012 at 0:06

jrad · Accepted Answer · 2012-08-04 00:09:38Z

2

Here's the conversion:

final double MAX_ANGLE = Math.toRadians(80);

Note that this is identical to saying:

final double MAX_ANGLE = 80 * Math.PI / 180;

answered Aug 4, 2012 at 0:09

jrad

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5 Comments

Dennis Meng Over a year ago

And of course, there's the Math.toDegrees function just in case you need it in degrees again.

WIllJBD Over a year ago

One more quetion, the number that i get from double angle = Math.cos((adj/hyp)); is a decimal like "0.7231" do i neet to multiply this number by 100, then conver it to radians as well?

jrad Over a year ago

Cosine doesn't return an angle. It's the ratio between the adjacent side and the hypotenuse of a triangle.

WIllJBD Over a year ago

ok looks like what I was looking for was acos(), this is what happens when you wait 3 years between highschool and college, and dont use angles

jrad Over a year ago

Yup, inverse cosine gets you the angle.

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