+static gp_Circ2d* newCirc2d(const std::shared_ptr<GeomAPI_Pnt2d>& theFirstPoint,
+ const std::shared_ptr<GeomAPI_Pnt2d>& theSecondPoint,
+ const std::shared_ptr<GeomAPI_Pnt2d>& theThirdPoint)
+{
+ gp_XY aFirstPnt(theFirstPoint->x(), theFirstPoint->y());
+ gp_XY aSecondPnt(theSecondPoint->x(), theSecondPoint->y());
+ gp_XY aThirdPnt(theThirdPoint->x(), theThirdPoint->y());
+
+ gp_XY aVec12 = aSecondPnt - aFirstPnt;
+ gp_XY aVec23 = aThirdPnt - aSecondPnt;
+ gp_XY aVec31 = aFirstPnt - aThirdPnt;
+
+ // coefficients to calculate center
+ double aCoeff1, aCoeff2, aCoeff3;
+
+ // square of parallelogram
+ double aSquare2 = aVec12.Crossed(aVec23);
+ aSquare2 *= aSquare2 * 2.0;
+ if (aSquare2 < 1.e-20) {
+ // if two points are equal, build a circle on two different points as on diameter
+ double aSqLen12 = aVec12.SquareModulus();
+ double aSqLen23 = aVec23.SquareModulus();
+ double aSqLen31 = aVec31.SquareModulus();
+ if (aSqLen12 < Precision::SquareConfusion() &&
+ aSqLen23 < Precision::SquareConfusion() &&
+ aSqLen31 < Precision::SquareConfusion())
+ return NULL;
+ aCoeff1 = aCoeff2 = aCoeff3 = 1.0 / 3.0;
+ }
+ else {
+ aCoeff1 = aVec23.Dot(aVec23) / aSquare2 * aVec12.Dot(aVec31.Reversed());
+ aCoeff2 = aVec31.Dot(aVec31) / aSquare2 * aVec23.Dot(aVec12.Reversed());
+ aCoeff3 = aVec12.Dot(aVec12) / aSquare2 * aVec31.Dot(aVec23.Reversed());
+ }
+ // center
+ gp_XY aCenter = aFirstPnt * aCoeff1 + aSecondPnt * aCoeff2 + aThirdPnt * aCoeff3;
+ // radius
+ double aRadius = (aFirstPnt - aCenter).Modulus();
+
+ gp_Dir2d aDir(aFirstPnt - aCenter);
+ return newCirc2d(aCenter.X(), aCenter.Y(), aDir, aRadius);
+}
+