added: utility function to lower/raise order of a Bspline basis

and tests

src/Utility/SplineUtils.C

@@ -309,6 +309,30 @@ Go::SplineVolume* SplineUtils::project (const Go::SplineVolume* volume,
 }
 
 
+Go::BsplineBasis SplineUtils::adjustBasis (const Go::BsplineBasis& basis,
+                                           SplineUtils::AdjustOp adjust)
+{
+  if (adjust == AdjustOp::Original)
+    return basis;
+
+  std::vector<double> knots;
+  basis.knotsSimple(knots);
+  std::vector<int> mult;
+  basis.knotMultiplicities(mult);
+  std::vector<int> cont(knots.size());
+  cont.front() = cont.back() = -1;
+  int order = basis.order();
+  int start_cont = adjust == AdjustOp::Lower ? order-2 : order;
+  int mult_adjust = adjust == AdjustOp::Lower ? 0 : 1;
+  int new_order = adjust == AdjustOp::Lower ? order - 1 : order + 1;
+  for (size_t i = 1; i < knots.size()-1; ++i)
+    cont[i] = start_cont - (mult[i] == 1 ? 1 : mult[i] + mult_adjust);
+
+  std::vector<double> newknot = SplineUtils::buildKnotVector(new_order-1, knots, cont);
+  return Go::BsplineBasis(new_order, newknot.begin(), newknot.end());
+}
+
+
 std::vector<double> SplineUtils::buildKnotVector(int p,
                                                  const std::vector<double>& knots,
                                                  const std::vector<int>& cont)

src/Utility/SplineUtils.h

@@ -27,6 +27,7 @@ namespace Go {
   struct BasisDerivsSf3;
   struct BasisDerivs;
   struct BasisDerivs2;
+  class BsplineBasis;
   class SplineCurve;
   class SplineSurface;
   class SplineVolume;
@@ -82,6 +83,17 @@ namespace SplineUtils //! Various utility functions on spline objects.
                             const FunctionBase& f,
                             int nComp = 1, Real time = Real(0));
 
+  //! \brief Enumeration of basis adjustment operations.
+  enum class AdjustOp {
+    Lower,    //!< Lower order by one
+    Original, //!< Keep original
+    Raise,    //!< Raise order by one
+  };
+
+  //! \brief Returns a basis adjusted according to the given operation.
+  Go::BsplineBasis adjustBasis(const Go::BsplineBasis& basis,
+                               AdjustOp adjust);
+
   //! \brief Builds a knot vector from a given polynomial order, knots and continuities.
   std::vector<double> buildKnotVector(int p, const std::vector<double>& simple_knots,
                                       const std::vector<int>& continuities);

src/Utility/Test/TestSplineUtils.C

@@ -12,10 +12,11 @@
 
 #include "SplineUtils.h"
 #include "GoTools/utils/Point.h"
-#include "GoTools/geometry/SplineSurface.h"
+#include <GoTools/geometry/BsplineBasis.h>
 #include "GoTools/geometry/Line.h"
 #include "GoTools/geometry/Disc.h"
 #include "GoTools/geometry/Plane.h"
+#include "GoTools/geometry/SplineSurface.h"
 #include "GoTools/trivariate/SphereVolume.h"
 #include "GoTools/trivariate/SplineVolume.h"
 #include "ExprFunctions.h"
@@ -450,3 +451,75 @@ TEST(TestSplineUtils, BuildKnotVector)
   for (size_t i = 0; i < ref.size(); ++i)
     EXPECT_FLOAT_EQ(ref[i], res[i]);
 }
+
+
+namespace {
+
+struct AdjustBasisTest {
+  int order_in;
+  std::vector<double> knots_in;
+  SplineUtils::AdjustOp op;
+  std::vector<double> knots_out;
+};
+
+using Op = SplineUtils::AdjustOp;
+
+const std::vector<AdjustBasisTest> tests = {
+  // p1 -> p1
+  {2, {0.0, 0.0, 1.0, 1.0}, Op::Original,
+      {0.0, 0.0, 1.0, 1.0}},
+
+  // p1 -> p2
+  {2, {0.0, 0.0, 1.0, 1.0}, Op::Raise,
+      {0.0, 0.0, 0.0, 1.0, 1.0, 1.0}},
+  // p1 -> p2, extra knot
+  {2, {0.0, 0.0, 0.5, 1.0, 1.0}, Op::Raise,
+      {0.0, 0.0, 0.0, 0.5, 1.0, 1.0, 1.0}},
+  // p2 -> p3, extra knot
+  {3, {0.0, 0.0, 0.0, 0.5, 1.0, 1.0, 1.0}, Op::Raise,
+      {0.0, 0.0, 0.0, 0.0, 0.5, 1.0, 1.0, 1.0, 1.0}},
+  // p2 -> p3, reduced cont
+  {3, {0.0, 0.0, 0.0, 0.5, 0.5, 1.0, 1.0, 1.0}, Op::Raise,
+      {0.0, 0.0, 0.0, 0.0, 0.5, 0.5, 0.5, 1.0, 1.0, 1.0, 1.0}},
+  //p3 -> p4
+  {4, {0.0, 0.0, 0.0, 0.0, 1.0, 1.0, 1.0, 1.0}, Op::Raise,
+      {0.0, 0.0, 0.0, 0.0, 0.0, 1.0, 1.0, 1.0, 1.0, 1.0}},
+  //p3 -> p4, reduced cont
+  {4, {0.0, 0.0, 0.0, 0.0, 0.5, 0.5, 1.0, 1.0, 1.0, 1.0}, Op::Raise,
+      {0.0, 0.0, 0.0, 0.0, 0.0, 0.5, 0.5, 0.5, 1.0, 1.0, 1.0, 1.0, 1.0}},
+
+  //p2 -> p1
+  {3, {0.0, 0.0, 0.0, 1.0, 1.0, 1.0}, Op::Lower,
+      {0.0, 0.0, 1.0, 1.0}},
+  //p2 -> p1, extra knot
+  {3, {0.0, 0.0, 0.0, 0.5, 1.0, 1.0, 1.0}, Op::Lower,
+      {0.0, 0.0, 0.5, 1.0, 1.0}},
+  //p3 -> p2, reduced cont
+  {4, {0.0, 0.0, 0.0, 0.0, 0.5, 0.5, 1.0, 1.0, 1.0, 1.0}, Op::Lower,
+      {0.0, 0.0, 0.0, 0.5, 0.5, 1.0, 1.0, 1.0}},
+  //p4 -> p3
+  {5, {0.0, 0.0, 0.0, 0.0, 0.0, 1.0, 1.0, 1.0, 1.0, 1.0}, Op::Lower,
+      {0.0, 0.0, 0.0, 0.0, 1.0, 1.0, 1.0, 1.0}},
+};
+
+}
+
+class TestSplineUtils : public testing::Test,
+                        public testing::WithParamInterface<AdjustBasisTest>
+{
+};
+
+
+TEST_P(TestSplineUtils, AdjustBasis)
+{
+  Go::BsplineBasis basis_in(GetParam().order_in,
+                            GetParam().knots_in.begin(),
+                            GetParam().knots_in.end());
+
+  const Go::BsplineBasis res = SplineUtils::adjustBasis(basis_in,GetParam().op);
+  const std::vector<double> out{res.begin(), res.end()};
+  EXPECT_EQ(out, GetParam().knots_out);
+}
+
+
+INSTANTIATE_TEST_SUITE_P(TestSplineUtils, TestSplineUtils, testing::ValuesIn(tests));