Geometry: Refacto and fix purge method.

src/Model/Geometry/PointXYZ.py

@@ -368,5 +368,10 @@ class PointXYZ(Point):
         a = PointXYZ.distance(p1, p2)
         b = PointXYZ.distance(p2, p3)
         c = PointXYZ.distance(p3, p1)
-        s = (a + b + c) / 2
-        return (s*(s-a) * (s-b)*(s-c)) ** 0.5
+
+        s = float((a + b + c) / 2)
+        res = (
+            s * abs(s - a) * abs(s - b) * abs(s - c)
+        ) ** 0.5
+
+        return res