Hi,
This is how I do it:
/**
* @param a_Point2D
* @param b_Point2D
* @param c_Point2D
* @return The inside Angle at b_Point for a Linear Ring assuming the ring
* is clockwise and the Linear Ring Sequence is a_Point, b_Point, c_Point.
*/
public static double getInsideAngleClockwise(
Point2D a_Point2D,
Point2D b_Point2D,
Point2D c_Point2D) {
double angle_aby = (Math.PI * 2.0d) - a_Point2D.getAngle(b_Point2D);
//double angle_aby_deg = getRadToDeg(angle_aby);
double angle_bcy = Math.PI - b_Point2D.getAngle(c_Point2D);
//double angle_bcy_deg = getRadToDeg(angle_bcy);
double result = angle_bcy - angle_aby;
if (result < 0) {
result = (Math.PI * 2.0d) + result;
}
//double result_deg = getRadToDeg(result);
return result;
}
Here is the getAngle(Point2D) method in my Point2D class:
/**
* Imprecise
* @param a_Point2D
* @return Angle to the y axis clockwise. Default 0.0d.
*/
public double getAngle(Point2D a_Point2D) {
double dx = a_Point2D._x.doubleValue() - _x.doubleValue();
double dy = a_Point2D._y.doubleValue() - _y.doubleValue();
if (dy == 0.0d) {
if (dx == 0.0d) {
return 0.0d;
} else {
if (dx > 0.0d) {
return Math.PI / 2.0d;
} else {
return (3.0d * Math.PI) / 2.0d;
}
}
} else {
if (dy > 0.0d) {
if (dx == 0.0d) {
return 0.0d;
} else {
if (dx > 0.0d) {
return Math.atan(dx / dy);
} else {
return (2.0d * Math.PI) - Math.atan(Math.abs(dx) / dy);
}
}
} else {
// dy < 0.0d
if (dx == 0.0d) {
return Math.PI;
} else {
if (dx > 0.0d) {
return Math.PI - Math.atan(dx / Math.abs(dy));
} else {
return Math.PI + Math.atan(Math.abs(dx) / Math.abs(dy));
}
}
}
}
}
BTW I'm working to improving precision and provide arbitrary fixed decimal
precision for these kinds of methods in my vector code (which is all open
source). Basically I use BigDecimal for each coordinate and the methods will
return a BigDecimal. The methods will also input an integer scale value which
will specif the number of decimal places for which the returned result must be
accurate.
Best wishes,
Andy
http://www.geog.leeds.ac.uk/people/a.turner/
-----Original Message-----
From: Pyro14 [mailto:[email protected]]
Sent: 10 April 2010 17:45
To: [email protected]
Subject: [Geotools-gt2-users] Angle between 3 points
Hi all,
can anybody tell me how to calculate the angle between 3 points?
Thx Pyro
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