diff --git a/src/Mod/Sketcher/App/planegcs/GCS.cpp b/src/Mod/Sketcher/App/planegcs/GCS.cpp
index 636f9899fe..4a3dd4e58a 100644
--- a/src/Mod/Sketcher/App/planegcs/GCS.cpp
+++ b/src/Mod/Sketcher/App/planegcs/GCS.cpp
@@ -1298,19 +1298,19 @@ int System::addConstraintInternalAlignmentBSplineControlPoint(BSpline &b, Circle
 //points are supplied, p is used for first curve and p2 for second, yielding a
 //remote angle computation (this is useful when the endpoints haven't) been
 //made coincident yet
-double System::calculateAngleViaPoint(Curve &crv1, Curve &crv2, Point &p)
+double System::calculateAngleViaPoint(const Curve &crv1, const Curve &crv2, Point &p) const
 {
     return calculateAngleViaPoint(crv1, crv2, p, p);
 }
 
-double System::calculateAngleViaPoint(Curve &crv1, Curve &crv2, Point &p1, Point &p2)
+double System::calculateAngleViaPoint(const Curve &crv1, const Curve &crv2, Point &p1, Point &p2) const
 {
     GCS::DeriVector2 n1 = crv1.CalculateNormal(p1);
     GCS::DeriVector2 n2 = crv2.CalculateNormal(p2);
     return atan2(-n2.x*n1.y+n2.y*n1.x, n2.x*n1.x + n2.y*n1.y);
 }
 
-void System::calculateNormalAtPoint(Curve &crv, Point &p, double &rtnX, double &rtnY)
+void System::calculateNormalAtPoint(const Curve &crv, const Point &p, double &rtnX, double &rtnY) const
 {
     GCS::DeriVector2 n1 = crv.CalculateNormal(p);
     rtnX = n1.x;
diff --git a/src/Mod/Sketcher/App/planegcs/GCS.h b/src/Mod/Sketcher/App/planegcs/GCS.h
index 14a7fb4bba..7c5f3ee916 100644
--- a/src/Mod/Sketcher/App/planegcs/GCS.h
+++ b/src/Mod/Sketcher/App/planegcs/GCS.h
@@ -325,9 +325,9 @@ namespace GCS
         int addConstraintInternalAlignmentParabolaFocus(Parabola &e, Point &p1, int tagId=0, bool driving = true);
         int addConstraintInternalAlignmentBSplineControlPoint(BSpline &b, Circle &c, int poleindex, int tag=0, bool driving = true);
 
-        double calculateAngleViaPoint(Curve &crv1, Curve &crv2, Point &p);
-        double calculateAngleViaPoint(Curve &crv1, Curve &crv2, Point &p1, Point &p2);
-        void calculateNormalAtPoint(Curve &crv, Point &p, double &rtnX, double &rtnY);
+        double calculateAngleViaPoint(const Curve &crv1, const Curve &crv2, Point &p) const;
+        double calculateAngleViaPoint(const Curve &crv1, const Curve &crv2, Point &p1, Point &p2) const;
+        void calculateNormalAtPoint(const Curve &crv, const Point &p, double &rtnX, double &rtnY) const;
 
         // Calculates errors of all constraints which have a tag equal to
         // the one supplied. Individual errors are summed up using RMS.
diff --git a/src/Mod/Sketcher/App/planegcs/Geo.cpp b/src/Mod/Sketcher/App/planegcs/Geo.cpp
index d805a8be47..fe96c9fbc3 100644
--- a/src/Mod/Sketcher/App/planegcs/Geo.cpp
+++ b/src/Mod/Sketcher/App/planegcs/Geo.cpp
@@ -30,7 +30,7 @@
 
 namespace GCS{
 
-DeriVector2::DeriVector2(const Point &p, double *derivparam)
+DeriVector2::DeriVector2(const Point &p, const double *derivparam)
 {
     x=*p.x; y=*p.y;
     dx=0.0; dy=0.0;
@@ -88,7 +88,7 @@ DeriVector2 DeriVector2::divD(double val, double dval) const
                        );
 }
 
-DeriVector2 Curve::Value(double /*u*/, double /*du*/, double* /*derivparam*/)
+DeriVector2 Curve::Value(double /*u*/, double /*du*/, const double* /*derivparam*/) const
 {
     assert(false /*Value() is not implemented*/);
     return DeriVector2();
@@ -96,15 +96,16 @@ DeriVector2 Curve::Value(double /*u*/, double /*du*/, double* /*derivparam*/)
 
 //----------------Line
 
-DeriVector2 Line::CalculateNormal(Point &/*p*/, double* derivparam)
+DeriVector2 Line::CalculateNormal(const Point &p, const double* derivparam) const
 {
+    (void) p;
     DeriVector2 p1v(p1, derivparam);
     DeriVector2 p2v(p2, derivparam);
 
     return p2v.subtr(p1v).rotate90ccw();
 }
 
-DeriVector2 Line::Value(double u, double du, double* derivparam)
+DeriVector2 Line::Value(double u, double du, const double* derivparam) const
 {
     DeriVector2 p1v(p1, derivparam);
     DeriVector2 p2v(p2, derivparam);
@@ -138,7 +139,7 @@ Line* Line::Copy()
 
 //---------------circle
 
-DeriVector2 Circle::CalculateNormal(Point &p, double* derivparam)
+DeriVector2 Circle::CalculateNormal(const Point &p, const double* derivparam) const
 {
     DeriVector2 cv (center, derivparam);
     DeriVector2 pv (p, derivparam);
@@ -146,7 +147,7 @@ DeriVector2 Circle::CalculateNormal(Point &p, double* derivparam)
     return cv.subtr(pv);
 }
 
-DeriVector2 Circle::Value(double u, double du, double* derivparam)
+DeriVector2 Circle::Value(double u, double du, const double* derivparam) const
 {
     //(x,y) = center + cos(u)*(r,0) + sin(u)*(0,r)
 
@@ -214,7 +215,7 @@ Arc* Arc::Copy()
 //--------------ellipse
 
 //this function is exposed to allow reusing pre-filled derivectors in constraints code
-double Ellipse::getRadMaj(const DeriVector2 &center, const DeriVector2 &f1, double b, double db, double &ret_dRadMaj)
+double Ellipse::getRadMaj(const DeriVector2 &center, const DeriVector2 &f1, double b, double db, double &ret_dRadMaj) const
 {
     double cf, dcf;
     cf = f1.subtr(center).length(dcf);
@@ -224,7 +225,7 @@ double Ellipse::getRadMaj(const DeriVector2 &center, const DeriVector2 &f1, doub
 }
 
 //returns major radius. The derivative by derivparam is returned into ret_dRadMaj argument.
-double Ellipse::getRadMaj(double *derivparam, double &ret_dRadMaj)
+double Ellipse::getRadMaj(double *derivparam, double &ret_dRadMaj) const
 {
     DeriVector2 c(center, derivparam);
     DeriVector2 f1(focus1, derivparam);
@@ -232,13 +233,13 @@ double Ellipse::getRadMaj(double *derivparam, double &ret_dRadMaj)
 }
 
 //returns the major radius (plain value, no derivatives)
-double Ellipse::getRadMaj()
+double Ellipse::getRadMaj() const
 {
     double dradmaj;//dummy
     return getRadMaj(0,dradmaj);
 }
 
-DeriVector2 Ellipse::CalculateNormal(Point &p, double* derivparam)
+DeriVector2 Ellipse::CalculateNormal(const Point &p, const double* derivparam) const
 {
     //fill some vectors in
     DeriVector2 cv (center, derivparam);
@@ -279,7 +280,7 @@ DeriVector2 Ellipse::CalculateNormal(Point &p, double* derivparam)
         return ret;
 }
 
-DeriVector2 Ellipse::Value(double u, double du, double* derivparam)
+DeriVector2 Ellipse::Value(double u, double du, const double* derivparam) const
 {
     //In local coordinate system, value() of ellipse is:
     //(a*cos(u), b*sin(u))
@@ -370,7 +371,7 @@ ArcOfEllipse* ArcOfEllipse::Copy()
 //---------------hyperbola
 
 //this function is exposed to allow reusing pre-filled derivectors in constraints code
-double Hyperbola::getRadMaj(const DeriVector2 &center, const DeriVector2 &f1, double b, double db, double &ret_dRadMaj)
+double Hyperbola::getRadMaj(const DeriVector2 &center, const DeriVector2 &f1, double b, double db, double &ret_dRadMaj) const
 {
     double cf, dcf;
     cf = f1.subtr(center).length(dcf);
@@ -382,7 +383,7 @@ double Hyperbola::getRadMaj(const DeriVector2 &center, const DeriVector2 &f1, do
 }
 
 //returns major radius. The derivative by derivparam is returned into ret_dRadMaj argument.
-double Hyperbola::getRadMaj(double *derivparam, double &ret_dRadMaj)
+double Hyperbola::getRadMaj(double *derivparam, double &ret_dRadMaj) const
 {
     DeriVector2 c(center, derivparam);
     DeriVector2 f1(focus1, derivparam);
@@ -390,13 +391,13 @@ double Hyperbola::getRadMaj(double *derivparam, double &ret_dRadMaj)
 }
 
 //returns the major radius (plain value, no derivatives)
-double Hyperbola::getRadMaj()
+double Hyperbola::getRadMaj() const
 {
     double dradmaj;//dummy
     return getRadMaj(0,dradmaj);
 }
 
-DeriVector2 Hyperbola::CalculateNormal(Point &p, double* derivparam)
+DeriVector2 Hyperbola::CalculateNormal(const Point &p, const double* derivparam) const
 {
     //fill some vectors in
     DeriVector2 cv (center, derivparam);
@@ -416,7 +417,7 @@ DeriVector2 Hyperbola::CalculateNormal(Point &p, double* derivparam)
     return ret;
 }
 
-DeriVector2 Hyperbola::Value(double u, double du, double* derivparam)
+DeriVector2 Hyperbola::Value(double u, double du, const double* derivparam) const
 {
 
     //In local coordinate system, value() of hyperbola is:
@@ -505,7 +506,7 @@ ArcOfHyperbola* ArcOfHyperbola::Copy()
 
 //---------------parabola
 
-DeriVector2 Parabola::CalculateNormal(Point &p, double* derivparam)
+DeriVector2 Parabola::CalculateNormal(const Point &p, const double* derivparam) const
 {
     //fill some vectors in
     DeriVector2 cv (vertex, derivparam);
@@ -522,7 +523,7 @@ DeriVector2 Parabola::CalculateNormal(Point &p, double* derivparam)
     return ret;
 }
 
-DeriVector2 Parabola::Value(double u, double du, double* derivparam)
+DeriVector2 Parabola::Value(double u, double du, const double* derivparam) const
 {
 
     //In local coordinate system, value() of parabola is:
@@ -607,7 +608,7 @@ ArcOfParabola* ArcOfParabola::Copy()
 }
 
 // bspline
-DeriVector2 BSpline::CalculateNormal(Point& p, double* derivparam)
+DeriVector2 BSpline::CalculateNormal(const Point &p, const double* derivparam) const
 {
     // place holder
     DeriVector2 ret;
@@ -651,7 +652,7 @@ DeriVector2 BSpline::CalculateNormal(Point& p, double* derivparam)
     return ret;
 }
 
-DeriVector2 BSpline::Value(double /*u*/, double /*du*/, double* /*derivparam*/)
+DeriVector2 BSpline::Value(double /*u*/, double /*du*/, const double* /*derivparam*/) const
 {
     // place holder
     DeriVector2 ret = DeriVector2();
diff --git a/src/Mod/Sketcher/App/planegcs/Geo.h b/src/Mod/Sketcher/App/planegcs/Geo.h
index cb234285f0..0fd9b3a2bb 100644
--- a/src/Mod/Sketcher/App/planegcs/Geo.h
+++ b/src/Mod/Sketcher/App/planegcs/Geo.h
@@ -55,7 +55,7 @@ namespace GCS
         DeriVector2(){x=0; y=0; dx=0; dy=0;}
         DeriVector2(double x, double y) {this->x = x; this->y = y; this->dx = 0; this->dy = 0;}
         DeriVector2(double x, double y, double dx, double dy) {this->x = x; this->y = y; this->dx = dx; this->dy = dy;}
-        DeriVector2(const Point &p, double* derivparam);
+        DeriVector2(const Point &p, const double* derivparam);
         double x, dx;
         double y, dy;
 
@@ -100,7 +100,7 @@ namespace GCS
         //derivparam is a pointer to a curve parameter (or point coordinate) to
         // compute the derivative for. The derivative is returned through dx,dy
         // fields of DeriVector2.
-        virtual DeriVector2 CalculateNormal(Point &p, double* derivparam = 0) = 0;
+        virtual DeriVector2 CalculateNormal(const Point &p, const double* derivparam = 0) const = 0;
 
         /**
          * @brief Value: returns point (vector) given the value of parameter
@@ -109,7 +109,7 @@ namespace GCS
          * @param derivparam: pointer to sketch parameter to calculate the derivative for
          * @return
          */
-        virtual DeriVector2 Value(double u, double du, double* derivparam = 0);
+        virtual DeriVector2 Value(double u, double du, const double* derivparam = 0) const;
 
         //adds curve's parameters to pvec (used by constraints)
         virtual int PushOwnParams(VEC_pD &pvec) = 0;
@@ -126,11 +126,11 @@ namespace GCS
         virtual ~Line(){}
         Point p1;
         Point p2;
-        DeriVector2 CalculateNormal(Point &p, double* derivparam = 0);
-        DeriVector2 Value(double u, double du, double* derivparam = 0);
-        virtual int PushOwnParams(VEC_pD &pvec);
-        virtual void ReconstructOnNewPvec (VEC_pD &pvec, int &cnt);
-        virtual Line* Copy();
+        DeriVector2 CalculateNormal(const Point &p, const double* derivparam = 0) const override;
+        DeriVector2 Value(double u, double du, const double* derivparam = 0) const override;
+        virtual int PushOwnParams(VEC_pD &pvec) override;
+        virtual void ReconstructOnNewPvec (VEC_pD &pvec, int &cnt) override;
+        virtual Line* Copy() override;
     };
 
     class Circle: public Curve
@@ -140,11 +140,11 @@ namespace GCS
         virtual ~Circle(){}
         Point center;
         double *rad;
-        DeriVector2 CalculateNormal(Point &p, double* derivparam = 0);
-        DeriVector2 Value(double u, double du, double* derivparam = 0);
-        virtual int PushOwnParams(VEC_pD &pvec);
-        virtual void ReconstructOnNewPvec (VEC_pD &pvec, int &cnt);
-        virtual Circle* Copy();
+        DeriVector2 CalculateNormal(const Point &p, const double* derivparam = 0) const override;
+        DeriVector2 Value(double u, double du, const double* derivparam = 0) const override;
+        virtual int PushOwnParams(VEC_pD &pvec) override;
+        virtual void ReconstructOnNewPvec (VEC_pD &pvec, int &cnt) override;
+        virtual Circle* Copy() override;
     };
 
     class Arc: public Circle
@@ -158,19 +158,19 @@ namespace GCS
         Point start;
         Point end;
         //Point center; //inherited
-        virtual int PushOwnParams(VEC_pD &pvec);
-        virtual void ReconstructOnNewPvec (VEC_pD &pvec, int &cnt);
-        virtual Arc* Copy();
+        virtual int PushOwnParams(VEC_pD &pvec) override;
+        virtual void ReconstructOnNewPvec (VEC_pD &pvec, int &cnt) override;
+        virtual Arc* Copy() override;
     };
 
     class MajorRadiusConic: public Curve
     {
     public:
         virtual ~MajorRadiusConic(){}
-        virtual double getRadMaj(const DeriVector2 &center, const DeriVector2 &f1, double b, double db, double &ret_dRadMaj) = 0;
-        virtual double getRadMaj(double* derivparam, double &ret_dRadMaj) = 0;
-        virtual double getRadMaj() = 0;
-        DeriVector2 CalculateNormal(Point &p, double* derivparam = 0) = 0;
+        virtual double getRadMaj(const DeriVector2 &center, const DeriVector2 &f1, double b, double db, double &ret_dRadMaj) const = 0;
+        virtual double getRadMaj(double* derivparam, double &ret_dRadMaj) const = 0;
+        virtual double getRadMaj() const = 0;
+        //DeriVector2 CalculateNormal(Point &p, double* derivparam = 0) = 0;
     };
 
     class Ellipse: public MajorRadiusConic
@@ -181,14 +181,14 @@ namespace GCS
         Point center;
         Point focus1;
         double *radmin;
-        virtual double getRadMaj(const DeriVector2 &center, const DeriVector2 &f1, double b, double db, double &ret_dRadMaj);
-        virtual double getRadMaj(double* derivparam, double &ret_dRadMaj);
-        virtual double getRadMaj();
-        DeriVector2 CalculateNormal(Point &p, double* derivparam = 0);
-        DeriVector2 Value(double u, double du, double* derivparam = 0);
-        virtual int PushOwnParams(VEC_pD &pvec);
-        virtual void ReconstructOnNewPvec (VEC_pD &pvec, int &cnt);
-        virtual Ellipse* Copy();
+        virtual double getRadMaj(const DeriVector2 &center, const DeriVector2 &f1, double b, double db, double &ret_dRadMaj) const override;
+        virtual double getRadMaj(double* derivparam, double &ret_dRadMaj) const override;
+        virtual double getRadMaj() const override;
+        DeriVector2 CalculateNormal(const Point &p, const double* derivparam = 0) const override;
+        DeriVector2 Value(double u, double du, const double* derivparam = 0) const override;
+        virtual int PushOwnParams(VEC_pD &pvec) override;
+        virtual void ReconstructOnNewPvec (VEC_pD &pvec, int &cnt) override;
+        virtual Ellipse* Copy() override;
     };
 
     class ArcOfEllipse: public Ellipse
@@ -204,9 +204,9 @@ namespace GCS
         //Point center;  //inherited
         //double *focus1.x; //inherited
         //double *focus1.y; //inherited
-        virtual int PushOwnParams(VEC_pD &pvec);
-        virtual void ReconstructOnNewPvec (VEC_pD &pvec, int &cnt);
-        virtual ArcOfEllipse* Copy();
+        virtual int PushOwnParams(VEC_pD &pvec) override;
+        virtual void ReconstructOnNewPvec (VEC_pD &pvec, int &cnt) override;
+        virtual ArcOfEllipse* Copy() override;
     };
 
     class Hyperbola: public MajorRadiusConic
@@ -217,14 +217,14 @@ namespace GCS
         Point center;
         Point focus1;
         double *radmin;
-        virtual double getRadMaj(const DeriVector2 &center, const DeriVector2 &f1, double b, double db, double &ret_dRadMaj);
-        virtual double getRadMaj(double* derivparam, double &ret_dRadMaj);
-        virtual double getRadMaj();
-        DeriVector2 CalculateNormal(Point &p, double* derivparam = 0);
-        virtual DeriVector2 Value(double u, double du, double* derivparam = 0);
-        virtual int PushOwnParams(VEC_pD &pvec);
-        virtual void ReconstructOnNewPvec (VEC_pD &pvec, int &cnt);
-        virtual Hyperbola* Copy();
+        virtual double getRadMaj(const DeriVector2 &center, const DeriVector2 &f1, double b, double db, double &ret_dRadMaj) const override;
+        virtual double getRadMaj(double* derivparam, double &ret_dRadMaj) const override;
+        virtual double getRadMaj() const override;
+        DeriVector2 CalculateNormal(const Point &p, const double* derivparam = 0) const override;;
+        virtual DeriVector2 Value(double u, double du, const double* derivparam = 0) const override;
+        virtual int PushOwnParams(VEC_pD &pvec) override;
+        virtual void ReconstructOnNewPvec (VEC_pD &pvec, int &cnt) override;
+        virtual Hyperbola* Copy() override;
     };
 
     class ArcOfHyperbola: public Hyperbola
@@ -238,9 +238,9 @@ namespace GCS
         Point start;
         Point end;
         // interface helpers
-        virtual int PushOwnParams(VEC_pD &pvec);
-        virtual void ReconstructOnNewPvec (VEC_pD &pvec, int &cnt);
-        virtual ArcOfHyperbola* Copy();
+        virtual int PushOwnParams(VEC_pD &pvec) override;
+        virtual void ReconstructOnNewPvec (VEC_pD &pvec, int &cnt) override;
+        virtual ArcOfHyperbola* Copy() override;
     };
 
     class Parabola: public Curve
@@ -250,11 +250,11 @@ namespace GCS
         virtual ~Parabola(){}
         Point vertex;
         Point focus1;
-        DeriVector2 CalculateNormal(Point &p, double* derivparam = 0);
-        virtual DeriVector2 Value(double u, double du, double* derivparam = 0);
-        virtual int PushOwnParams(VEC_pD &pvec);
-        virtual void ReconstructOnNewPvec (VEC_pD &pvec, int &cnt);
-        virtual Parabola* Copy();
+        DeriVector2 CalculateNormal(const Point &p, const double* derivparam = 0) const override;
+        virtual DeriVector2 Value(double u, double du, const double* derivparam = 0) const override;
+        virtual int PushOwnParams(VEC_pD &pvec) override;
+        virtual void ReconstructOnNewPvec (VEC_pD &pvec, int &cnt) override;
+        virtual Parabola* Copy() override;
     };
 
     class ArcOfParabola: public Parabola
@@ -268,9 +268,9 @@ namespace GCS
         Point start;
         Point end;
         // interface helpers
-        virtual int PushOwnParams(VEC_pD &pvec);
-        virtual void ReconstructOnNewPvec (VEC_pD &pvec, int &cnt);
-        virtual ArcOfParabola* Copy();
+        virtual int PushOwnParams(VEC_pD &pvec) override;
+        virtual void ReconstructOnNewPvec (VEC_pD &pvec, int &cnt) override;
+        virtual ArcOfParabola* Copy() override;
     };
 
     class BSpline: public Curve
@@ -293,11 +293,11 @@ namespace GCS
         bool periodic;
         VEC_I knotpointGeoids; // geoids of knotpoints as to index Geom array
         // interface helpers
-        DeriVector2 CalculateNormal(Point &p, double* derivparam = 0);
-        virtual DeriVector2 Value(double u, double du, double* derivparam = 0);
-        virtual int PushOwnParams(VEC_pD &pvec);
-        virtual void ReconstructOnNewPvec (VEC_pD &pvec, int &cnt);
-        virtual BSpline* Copy();
+        DeriVector2 CalculateNormal(const Point &p, const double* derivparam = 0) const override;;
+        virtual DeriVector2 Value(double u, double du, const double* derivparam = 0) const override;
+        virtual int PushOwnParams(VEC_pD &pvec) override;
+        virtual void ReconstructOnNewPvec (VEC_pD &pvec, int &cnt) override;
+        virtual BSpline* Copy() override;
     };
 
 } //namespace GCS