/**
* Computes the center of the circumscribed circle of the three input points.
*
* @throws ColinearPoints2DException if the 3 points are colinear
*/
public static Point2D circumCenter(Point2D p1, Point2D p2, Point2D p3) {
if (Point2D.isColinear(p1, p2, p3)) throw new ColinearPoints2DException(p1, p2, p3);
// create two median lines
StraightLine2D line12 = StraightLine2D.createMedian(p1, p2);
StraightLine2D line23 = StraightLine2D.createMedian(p2, p3);
// check medians are not parallel
assert !AbstractLine2D.isParallel(line12, line23)
: "If points are not colinear, medians should not be parallel";
// Compute intersection of the medians, and circle radius
Point2D center = AbstractLine2D.getIntersection(line12, line23);
// return the center
return center;
}
/**
* Computes intersections of a circle with a line. Returns an array of Point2D, of size 0, 1 or 2
* depending on the distance between circle and line. If there are 2 intersections points, the
* first one in the array is the first one on the line.
*
* @return a collection of intersection points
* @since 0.11.1
*/
public static Collection<Point2D> lineCircleIntersections(
LinearShape2D line, CircularShape2D circle) {
// initialize array of points (maximum 2 intersections)
ArrayList<Point2D> intersections = new ArrayList<Point2D>(2);
// extract parameters of the circle
Circle2D parent = circle.supportingCircle();
Point2D center = parent.center();
double radius = parent.radius();
// Compute line perpendicular to the test line, and going through the
// circle center
StraightLine2D perp = StraightLine2D.createPerpendicular(line, center);
// Compute distance between line and circle center
Point2D inter = perp.intersection(new StraightLine2D(line));
if (inter == null) {
throw new RuntimeException(
"Could not compute intersection point when computing line-cicle intersection");
}
double dist = inter.distance(center);
// if the distance is the radius of the circle, return the
// intersection point
if (abs(dist - radius) < Shape2D.ACCURACY) {
if (line.contains(inter) && circle.contains(inter)) intersections.add(inter);
return intersections;
}
// compute angle of the line, and distance between 'inter' point and
// each intersection point
double angle = line.horizontalAngle();
double d2 = sqrt(radius * radius - dist * dist);
// Compute position and angle of intersection points
Point2D p1 = Point2D.createPolar(inter, d2, angle + Math.PI);
Point2D p2 = Point2D.createPolar(inter, d2, angle);
// add points to the array only if they belong to the line
if (line.contains(p1) && circle.contains(p1)) intersections.add(p1);
if (line.contains(p2) && circle.contains(p2)) intersections.add(p2);
// return the result
return intersections;
}
/* (non-Javadoc)
* @see math.geom2d.circulinear.CirculinearCurve2D#transform(math.geom2d.transform.CircleInversion2D)
*/
public CircleLine2D transform(CircleInversion2D inv) {
// Extract inversion parameters
Point2D center = inv.center();
Point2D c1 = this.center();
// If circles are concentric, creates directly the new circle
if (center.distance(c1) < Shape2D.ACCURACY) {
double r0 = inv.radius();
double r2 = r0 * r0 / this.r;
return new Circle2D(center, r2, this.direct);
}
// line joining centers of the two circles
StraightLine2D centersLine = new StraightLine2D(center, c1);
// get the two intersection points with the line joining the circle centers
Collection<Point2D> points = this.intersections(centersLine);
if (points.size() < 2) {
throw new RuntimeException(
"Intersection of circle with line through center has less than 2 points");
}
Iterator<Point2D> iter = points.iterator();
Point2D p1 = iter.next();
Point2D p2 = iter.next();
// If the circle contains the inversion center, it transforms into a
// straight line
if (this.distance(center) < Shape2D.ACCURACY) {
// choose the intersection point that is not the center
double dist1 = center.distance(p1);
double dist2 = center.distance(p2);
Point2D p0 = dist1 < dist2 ? p2 : p1;
// transform the point, and return the perpendicular
p0 = p0.transform(inv);
return StraightLine2D.createPerpendicular(centersLine, p0);
}
// For regular cases, the circle transforms into an other circle
// transform the two extreme points of the circle,
// resulting in a diameter of the new circle
p1 = p1.transform(inv);
p2 = p2.transform(inv);
// compute center and diameter of transformed circle
double diam = p1.distance(p2);
c1 = Point2D.midPoint(p1, p2);
// create the transformed circle
boolean direct = !this.isDirect() ^ this.isInside(inv.center());
return new Circle2D(c1, diam / 2, direct);
}