Part: add function GetCircleCenter from CommandCreateGeo.cpp of the Sketcher module to the Geom2dCircle class in the Part module

src/Mod/Part/App/Geometry2d.cpp

@@ -909,6 +909,51 @@ PyObject *Geom2dCircle::getPyObject(void)
     return new Circle2dPy(static_cast<Geom2dCircle*>(this->clone()));
 }
 
+/*
+Find the centerpoint of a circle drawn through any 3 points:
+
+Given points p1-3, draw 2 lines: S12 and S23 which each connect two points.  From the
+midpoint of each line, draw a perpendicular line (S12p/S23p) across the circle.  These
+lines will cross at the centerpoint.
+
+Mathematically, line S12 will have a slope of m12 which can be determined.  Therefore,
+the slope m12p is -1/m12. Line S12p will have an equation of y = m12p*x + b12p.  b12p can
+be solved for using the midpoint of the line.  This can be done for both lines.  Since
+both S12p and S23p cross at the centerpoint, solving the two equations together will give
+the location of the centerpoint.
+*/
+Base::Vector2d Geom2dCircle::getCircleCenter (const Base::Vector2d &p1, const Base::Vector2d &p2, const Base::Vector2d &p3)
+{
+    Base::Vector2d u = p2-p1;
+    Base::Vector2d v = p3-p2;
+    Base::Vector2d w = p1-p3;
+
+    double uu =  u*u;
+    double vv =  v*v;
+    double ww =  w*w;
+
+    if (uu * vv * ww == 0)
+        THROWM(Base::ValueError,"Two points are coincident");
+
+    double uv = -(u*v);
+    double vw = -(v*w);
+    double uw = -(u*w);
+
+    double w0 = (2 * sqrt(uu * ww - uw * uw) * uw / (uu * ww));
+    double w1 = (2 * sqrt(uu * vv - uv * uv) * uv / (uu * vv));
+    double w2 = (2 * sqrt(vv * ww - vw * vw) * vw / (vv * ww));
+
+    double wx = w0 + w1 + w2;
+
+    if( wx == 0)
+        THROWM(Base::ValueError,"Points are collinear");
+
+    double x = (w0*p1.x + w1*p2.x + w2*p3.x)/wx;
+    double y = (w0*p1.y + w1*p2.y + w2*p3.y)/wx;
+
+    return Base::Vector2d(x, y);
+}
+
 // -------------------------------------------------
 
 TYPESYSTEM_SOURCE(Part::Geom2dArcOfCircle, Part::Geom2dArcOfConic)

src/Mod/Part/App/Geometry2d.h

@@ -43,6 +43,7 @@
 #include <memory>
 #include <Base/Persistence.h>
 #include <Base/Tools2D.h>
+#include <Mod/Part/PartGlobal.h>
 
 namespace Part {
 
@@ -267,6 +268,8 @@ public:
 
     const Handle(Geom2d_Geometry)& handle() const;
 
+    static Base::Vector2d getCircleCenter (const Base::Vector2d &p1, const Base::Vector2d &p2, const Base::Vector2d &p3);
+
 private:
     Handle(Geom2d_Circle) myCurve;
 };