Calculating the angle between two lines without having to calculate the slope? (Java)?
I have two Lines: L1 and L2. I want to calculate the angle between the two lines. L1 has points: `{(x1, y1), (x2, y2)}` and L2 has points: `{(x3, y3), (x4, y4)}`.
How can I calculate the angle formed between these two lines, without having to calculate the slopes? The problem I am currently having is that sometimes I have horizontal lines (lines along the x-axis) and the following formula fails (divide by zero exception):
arctan((m1 - m2) / (1 - (m1 * m2)))
where `m1` and `m2` are the slopes of line 1 and line 2 respectively. Is there a formula/algorithm that can calculate the angles between the two lines without ever getting divide-by-zero exceptions? Any help would be highly appreciated.
This is my code snippet:
// Calculates the angle formed between two lines
public static double angleBetween2Lines(Line2D line1, Line2D line2)
{
double slope1 = line1.getY1() - line1.getY2() / line1.getX1() - line1.getX2();
double slope2 = line2.getY1() - line2.getY2() / line2.getX1() - line2.getX2();
double angle = Math.atan((slope1 - slope2) / (1 - (slope1 * slope2)));
return angle;
}
Thanks.
the zero denominator occurs when the slopes are reciprocals. When the slopes are reciprocal the angle between the lines is pi/2 - 2*arctan(m1) if m1>0 and pi/2+2*arctan(m1) if m1<0.
