Removed Curve and Surface into ExtendedMethods.

src/GShark/Core/CurveHelpers.cs

@@ -0,0 +1,50 @@
+using GShark.ExtendedMethods;
+using GShark.Geometry;
+using GShark.Operation;
+using System.Collections.Generic;
+using System.Linq;
+
+namespace GShark.Core
+{
+    internal static class CurveHelpers
+    {
+        /// <summary>
+        /// Normalizes knot vectors of all curves to the same domain.
+        /// </summary>
+        internal static IList<NurbsCurve> NormalizedKnots(IList<NurbsCurve> curves)
+        {
+            // Unify knots, normalized them.
+            curves = curves
+                .Select(curve => curve.Knots.GetDomain(curve.Degree).Length > 1
+                    ? new NurbsCurve(curve.Degree, curve.Knots.Normalize(), curve.ControlPoints)
+                    : curve).ToList();
+
+            // Unify curves by knots.
+            KnotVector combinedKnots = curves.First().Knots.Copy();
+            foreach (NurbsCurve curve in curves.Skip(1))
+            {
+                combinedKnots.AddRange(curve.Knots.Where(k => !combinedKnots.Contains(k)).ToList());
+            }
+
+            curves = (from curve in curves
+                          let knotToInsert = combinedKnots.OrderBy(k => k).Where(k => !curve.Knots.Contains(k)).ToKnot()
+                          select Modify.CurveKnotRefine(curve, knotToInsert)).ToList();
+            return curves;
+        }
+
+        /// <summary>
+        /// Elevates degree of all curves to highest degree among all curves.
+        /// </summary>
+        internal static IList<NurbsCurve> NormalizedDegree(IList<NurbsCurve> curves)
+        {
+            // Unify curves by degree.
+            int targetDegree = curves.Max(c => c.Degree);
+            curves = curves
+                .Select(curve => curve.Degree != targetDegree
+                    ? Modify.ElevateDegree(curve, targetDegree)
+                    : curve).ToList();
+
+            return curves;
+        }
+    }
+}