diff --git a/EgtGeomKernel.rc b/EgtGeomKernel.rc
index dd55861..f4d2aa3 100644
Binary files a/EgtGeomKernel.rc and b/EgtGeomKernel.rc differ
diff --git a/EgtGeomKernel.vcxproj b/EgtGeomKernel.vcxproj
index b6cd7ba..960f459 100644
--- a/EgtGeomKernel.vcxproj
+++ b/EgtGeomKernel.vcxproj
@@ -116,6 +116,7 @@
       <MultiProcessorCompilation>true</MultiProcessorCompilation>
       <DebugInformationFormat>ProgramDatabase</DebugInformationFormat>
       <EnablePREfast>false</EnablePREfast>
+      <LanguageStandard>stdcpp17</LanguageStandard>
     </ClCompile>
     <Link>
       <SubSystem>Windows</SubSystem>
@@ -198,6 +199,7 @@ copy $(TargetPath) \EgtProg\DllD64</Command>
       <EnableParallelCodeGeneration>true</EnableParallelCodeGeneration>
       <WholeProgramOptimization>false</WholeProgramOptimization>
       <DebugInformationFormat>ProgramDatabase</DebugInformationFormat>
+      <LanguageStandard>stdcpp17</LanguageStandard>
     </ClCompile>
     <Link>
       <SubSystem>Windows</SubSystem>
diff --git a/SurfFlatRegion.cpp b/SurfFlatRegion.cpp
index 215f434..d2bd04a 100644
--- a/SurfFlatRegion.cpp
+++ b/SurfFlatRegion.cpp
@@ -143,11 +143,11 @@ SurfFlatRegion::AddSimpleExtLoop( ICurve* pCrv)
    else {
      // verifico che il piano della curva coincida con quello XY intrinseco
       plPlane.ToLoc( m_frF) ;
-      if ( ! ( plPlane.GetVersN().IsZplus()  ||  plPlane.GetVersN().IsZminus())  ||  abs( plPlane.GetDist()) > EPS_SMALL)
+      if ( ! plPlane.GetVersN().IsZ()  ||  abs( plPlane.GetDist()) > EPS_SMALL)
          return false ;
      // sistemo il senso di rotazione (deve essere CCW -> area > 0)
-      if ( ( plPlane.GetVersN().IsZplus()  &&  dArea < 0)  ||
-           ( plPlane.GetVersN().IsZminus()  &&  dArea > 0))
+      if ( ( plPlane.GetVersN().z > 0  &&  dArea < 0)  ||
+           ( plPlane.GetVersN().z < 0  &&  dArea > 0))
          pMyCrv->Invert() ;
    }
   // porto la curva nel riferimento intrinseco
@@ -283,10 +283,10 @@ SurfFlatRegion::AddSimpleIntLoop( ICurve* pCrv)
    Plane3d plPlane ;
    if ( ! pMyCrv->GetArea( plPlane, dArea))
       return false ;
-   if ( ! ( plPlane.GetVersN().IsZplus()  ||  plPlane.GetVersN().IsZminus())  ||  abs( plPlane.GetDist()) > EPS_SMALL)
+   if ( ! plPlane.GetVersN().IsZ()  ||  abs( plPlane.GetDist()) > EPS_SMALL)
       return false ;
-  // sistemo il senso di rotazione (deve essere CW -> se N==Z+ area < 0, se N==Z- area>0)
-   if ( ( plPlane.GetVersN().IsZplus()  &&  dArea > 0)  ||  ( plPlane.GetVersN().IsZminus()  &&  dArea < 0))
+  // sistemo il senso di rotazione (deve essere CW -> se N==Z+ area < 0, se N==Z- area > 0)
+   if ( ( plPlane.GetVersN().z > 0  &&  dArea > 0)  ||  ( plPlane.GetVersN().z < 0  &&  dArea < 0))
       pMyCrv->Invert() ;
   // verifico non abbia auto-intersezioni
    SelfIntersCurve sInt( *pMyCrv) ;