CODEWITHSUNDEEP
javaandroidcanvastrigonometry
HB.
HB.

Reputation: 4226

Calculate angle between two lines

After looking at the answers provided in this question, I created the following method:

private int angleOf(float x1, float x2, float y1, float y2) {
    final double deltaY = (y1 - y2);
    final double deltaX = (x2 - x1);
    final double result = Math.toDegrees(Math.atan2(deltaY, deltaX));
    return (int) ((result < 0) ? (360d + result) : result);
}

by using the above I will get the angle of each line , then I draw the text to my canvas, as shown below:

int topLine = angleOf(this.mPoints[5].x, this.mPoints[4].x, this.mPoints[5].y, this.mPoints[4].y);
int bottomLine = angleOf(this.mPoints[5].x, this.mPoints[6].x, this.mPoints[5].y, this.mPoints[6].y);

canvas.drawText(String.valueOf(360 - bottomLine + topLine)+"°", this.mPoints[5].x - 80.0f, this.mPoints[5].y, this.mTextPaint);


The above works fine, here is a example of my result:

exampleImage1

The problem I have is that the angle is measured from the x-axis and increasing anti-clockwise, as shown below:

image2

When the bottom line or the top line "crosses" the 0° (parallel to the x-axis), I would then get an incorrect angle.

Here is another image to demonstrate this issue:

image3

The angle between the blue lines are 90°, but instead I get 450°. This happens because of the calculation I used 360 - bottomLine + topLine.

Can someone please suggest a solution to this issue.

Thank you.

Upvotes: 4

Views: 1854

Answers (2)

user987339
user987339

Reputation: 10707

Use this method to calculate it properly:

private double angleOfDegrees(float x0, float y0, float x1, float y1) {
    double angle2 = Math.atan2(y1,x1);
    double angle1 = Math.atan2(y0,x0);

   return Math.toDegrees(angle2 - angle1) + 360) % 360;
}

Upvotes: 0

Madhuka Dilhan
Madhuka Dilhan

Reputation: 1416

You can use like this,out put value is radian coordinate point (0,0) other points (x1,y1) ,(x2,y2)

atan() = tan invers

private double angleOfRadian(float x1, float x2, float y1, float y2) {
     return java.lang.Math.atan(y2/x2)-java.lang.Math.atan(y1/x1);
}

Upvotes: 1

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