[Draft] Arc Tracker by 3points method

Added arcBy3Points method to arc tracker

src/Mod/Draft/DraftTrackers.py

@@ -505,7 +505,7 @@ class arcTracker(Tracker):
         self.recompute()
 
     def getAngle(self,pt):
-        "returns the angle of a given vector"
+        "returns the angle of a given vector in radians"
         c = self.trans.translation.getValue()
         center = Vector(c[0],c[1],c[2])
         rad = pt.sub(center)
@@ -514,7 +514,7 @@ class arcTracker(Tracker):
         return(a)
 
     def getAngles(self):
-        "returns the start and end angles"
+        "returns the start and end angles in degrees"
         return(self.startangle,self.endangle)
                 
     def setStartPoint(self,pt):
@@ -531,6 +531,21 @@ class arcTracker(Tracker):
         self.endangle = self.startangle + ap
         self.recompute()
 
+    def setBy3Points(self,p1,p2,p3):
+        "sets the arc by three points"
+        import Part
+        try:
+            arc=Part.ArcOfCircle(p1,p2,p3)
+        except: return
+        e=arc.toShape()
+        self.autoinvert = False
+        self.normal = e.Curve.Axis.negative() # axis is always in wrong direction
+        self.basevector = self.getDeviation()
+        self.setCenter(e.Curve.Center)
+        self.setRadius(e.Curve.Radius)
+        self.setStartPoint(p1)
+        self.setEndPoint(p3)
+
     def recompute(self):
         import Part,re
         if self.circle: 
@@ -570,7 +585,7 @@ class arcTracker(Tracker):
                 self.sep.addChild(self.circle)
             else:
                 FreeCAD.Console.PrintWarning("arcTracker.recompute() failed to read-in Inventor string\n")
-            
+
 
 class ghostTracker(Tracker):
     '''A Ghost tracker, that allows to copy whole object representations.