From 462efdab37d2feeaf50f42e802b6b6422bbba6cf Mon Sep 17 00:00:00 2001
From: wmayer <wmayer@users.sourceforge.net>
Date: Fri, 30 Oct 2020 13:55:31 +0100
Subject: [PATCH] Part: [skip ci] After removing a knot check if the B-spline
 is still valid

---
 src/Mod/Part/App/Geometry.cpp | 20 +++++++++++++++++---
 1 file changed, 17 insertions(+), 3 deletions(-)

diff --git a/src/Mod/Part/App/Geometry.cpp b/src/Mod/Part/App/Geometry.cpp
index 6346f066a5de..8bbf143b7246 100644
--- a/src/Mod/Part/App/Geometry.cpp
+++ b/src/Mod/Part/App/Geometry.cpp
@@ -1400,11 +1400,25 @@ void GeomBSplineCurve::increaseMultiplicity(int index, int multiplicity)
 bool GeomBSplineCurve::removeKnot(int index, int multiplicity, double tolerance)
 {
     try {
-        Handle(Geom_BSplineCurve) curve = Handle(Geom_BSplineCurve)::DownCast(this->handle());
-        return curve->RemoveKnot(index, multiplicity, tolerance) == Standard_True;
+        Handle(Geom_BSplineCurve) curve =Handle(Geom_BSplineCurve)::DownCast(myCurve->Copy());
+        if (curve->RemoveKnot(index, multiplicity, tolerance)) {
+
+            // It can happen that OCCT computes a negative weight but still claims the removal was successful
+            TColStd_Array1OfReal weights(1, curve->NbPoles());
+            curve->Weights(weights);
+            for (Standard_Integer i = weights.Lower(); i <= weights.Upper(); i++) {
+                double v = weights(i);
+                if (v <= gp::Resolution())
+                    return false;
+            }
+
+            myCurve = curve;
+            return true;
+        }
+
+        return false;
     }
     catch (Standard_Failure& e) {
-
         THROWM(Base::CADKernelError,e.GetMessageString())
     }
 }