Copyright 2012, Rodrigo Balerdi. Licensed under the GNU General Public License (GPL) Version 3 or later.
A year ago I needed free code to compute coplanar circle-to-circle intersections in Java and could not find any. So I wrote this and forgot to release it.
Construct a CircleCircleIntersection from two Circle instances c1 and c2 to solve an intersection. Note that degenerate circles (zero radius) cannot be constructed.
The type of an intersection will be one of:
COINCIDENT
CONCENTRIC_CONTAINED
ECCENTRIC_CONTAINED
INTERNALLY_TANGENT
OVERLAPPING
EXTERNALLY_TANGENT
SEPARATE
You can query the Type object for some generic properties of the type:
int getIntersectionPointCount(); // -1 if count is infinite (coincident circles)
boolean isConcentric();
boolean isContained();
boolean isTangent();
boolean isDisjoint();
The CircleCircleIntersection object itself will contain the immutable results of the intersection.
Results valid for all intersections:
Type type; // type of intersection
double distanceC1cC2c; // distance between circle centers
Results valid for eccentric circles:
Vector2 radicalPoint; // intersection between line connecting circle centers and radical line
double distanceC1cRadicalLine; // signed distances from circle centers to radical line
double distanceC2cRadicalLine; // (the direction to the other center is positive)
Vector2 versorC1cC2c; // direction versor from c1 center to c2 center
Vector2 versorRadicalLine; // direction versor of radical line
// (points to the left if looking from c1 center to c2 center)
Results valid for tangent circles:
Vector2 intersectionPoint; // intersection point
Results valid for overlapping circles:
Vector2 intersectionPoint1; // intersection points
Vector2 intersectionPoint2; // (point 1 is on the left if looking from c1 center to c2 center)
double distanceRadicalPointIntersectionPoints; // distance between radical point and either intersection point
Method valid for noncoincident circles:
Vector2[] getIntersectionPoints(); // array of 0, 1 or 2 intersection points (throws if coincident circles)