Index: /trunk/psLib/src/math/psEllipse.c
===================================================================
--- /trunk/psLib/src/math/psEllipse.c	(revision 9773)
+++ /trunk/psLib/src/math/psEllipse.c	(revision 9774)
@@ -45,7 +45,7 @@
     double f1 = 1.0 / PS_SQR(shape.sx) + 1.0 / PS_SQR(shape.sy);
     double f2 = 1.0 / PS_SQR(shape.sx) - 1.0 / PS_SQR(shape.sy);
-    double f3 = PS_SQR(f2) + 4*PS_SQR(shape.sxy);
+    double f3 = sqrt(PS_SQR(f2) + 4*PS_SQR(shape.sxy));
 
-    axes.theta = 0.5 * atan2 (-2.0*shape.sxy, f2) / 2.0;
+    axes.theta = 0.5 * atan2 (2*shape.sxy, f2);
     axes.major = sqrt (2.0 / (f1 - f3));
     axes.minor = sqrt (2.0 / (f1 + f3));