add ellipse as csg2d solid object

python/geom2d.py

@@ -1,5 +1,6 @@
 from .libngpy._geom2d import SplineGeometry, Solid2d, CSG2d, Rectangle, Circle, EdgeInfo, PointInfo
 from .meshing import meshsize
+import math as math
 
 unit_square = SplineGeometry()
 _pnts = [ (0,0), (1,0), (1,1), (0,1) ]
@@ -144,3 +145,34 @@ def cp(p_or_px, py_or_none = None):
         return EdgeInfo(control_point=p)
     else:
         return EdgeInfo(control_point=(p_or_px,py_or_none))
+
+
+def Ellipse(center, a, b, bc="ellipse", mat="ellipse"):
+    """Creates ellipse centered at point center with principle axis a and b.
+
+    Parameters
+    ---------
+    center : Vec2
+      center of ellipse
+    a : Vec2
+      first principle axis, needs to be perpendicular to b
+    b : Vec2
+      second principle axis, needs to be perpendicular to a
+    bc : string
+      boundary name
+    mat : string
+      material name
+    """
+    if abs(a[0]*b[0] + a[1]*b[1]) > 1e-12:
+        raise Exception("In Ellipse: principle axis a and b are not perpendicular")
+    
+    ellipse = Circle( center=(0,0), radius=1.0, mat=mat, bc=bc )
+    
+    alpha = math.pi/2-math.atan2(a[0],a[1])
+    r_a = math.sqrt(a[0]**2+a[1]**2)
+    r_b = math.sqrt(b[0]**2+b[1]**2)
+    ellipse.Scale( (r_a,r_b) )
+    ellipse.Rotate( alpha/math.pi*180, center=(0,0) )
+    ellipse.Move( center )
+    
+    return ellipse