diff --git a/EgtGraphics.rc b/EgtGraphics.rc
index 29a1242..25a60d7 100644
Binary files a/EgtGraphics.rc and b/EgtGraphics.rc differ
diff --git a/Scene.h b/Scene.h
index 65d7b72..1fd40d1 100644
--- a/Scene.h
+++ b/Scene.h
@@ -121,6 +121,7 @@ class Scene : public IEGrScene
       virtual bool ResetWinRect( void) ;
      // Snap
       virtual bool GetGraphicSnapPoint( int nSnap, const Point3d& ptWin, int nW, int nH, Point3d& ptSel) ;
+      virtual bool GetGridSnapPointZ( bool bSketch, const Point3d& ptWin, const Point3d& ptGrid, Point3d& ptSel) ;
 
    public :
      // Basic
@@ -159,11 +160,10 @@ class Scene : public IEGrScene
       bool DrawGeoLine( void) ;
       bool DrawWinRect( void) ;
      // Snap
-      bool GetGridSnapPoint( int nSnap, const Point3d& ptWin, Point3d& ptSel) ;
+      bool GetGridSnapPoint( bool bSketch, const Point3d& ptWin, Point3d& ptSel) ;
       bool GetSelectedSnapPoint( int nSnap, const Point3d& ptWin, int nW, int nH, Point3d& ptSel) ;
       bool VerifySnapPoint( const Point3d& ptP, const Point3d& ptWin, double& dMinSqDist) ;
 
-
    private :
       HDC          m_hDC ;                // Device Context
       HGLRC        m_hRC ;                // OpenGL Rendering Context 
diff --git a/SceneBasic.cpp b/SceneBasic.cpp
index f60f604..5ccd937 100644
--- a/SceneBasic.cpp
+++ b/SceneBasic.cpp
@@ -25,7 +25,7 @@
 using namespace std ;
 
 //--------------------------- Constants --------------------------------------
-static const double MIN_EXTENSION = 50 ;
+static const double MIN_EXTENSION = 250 ;
 static const double MIN_W_H = 0.01 ;
 static const double MIN_ZCLIP_EXT = 5000 ;
 
diff --git a/SceneSnap.cpp b/SceneSnap.cpp
index fc5d316..51e4722 100644
--- a/SceneSnap.cpp
+++ b/SceneSnap.cpp
@@ -31,7 +31,7 @@ Scene::GetGraphicSnapPoint( int nSnap, const Point3d& ptWin, int nW, int nH, Poi
 {
   // se Snap Sketch o Grid, devo trovare il punto sulla griglia
    if ( nSnap == SP_SKETCH  ||  nSnap == SP_GRID)
-      return GetGridSnapPoint( nSnap, ptWin, ptSel) ;
+      return GetGridSnapPoint( ( nSnap == SP_SKETCH), ptWin, ptSel) ;
   // altrimenti devo trovare il punto dall'entitą inquadrata
    else
       return GetSelectedSnapPoint( nSnap, ptWin, nW, nH, ptSel) ;
@@ -39,7 +39,7 @@ Scene::GetGraphicSnapPoint( int nSnap, const Point3d& ptWin, int nW, int nH, Poi
 
 //----------------------------------------------------------------------------
 bool
-Scene::GetGridSnapPoint( int nSnap, const Point3d& ptWin, Point3d& ptSel)
+Scene::GetGridSnapPoint( bool bSketch, const Point3d& ptWin, Point3d& ptSel)
 {
   // calcolo un punto e la direzione della linea di mira
    Point3d ptLine ;
@@ -57,7 +57,7 @@ Scene::GetGridSnapPoint( int nSnap, const Point3d& ptWin, Point3d& ptSel)
   // porto il punto sul piano di griglia
    ptSel.ToLoc( m_frGrid) ;
   // se punto grid, devo arrotondare al nodo di griglia pił vicino
-   if ( nSnap == SP_GRID) {
+   if ( ! bSketch) {
       ptSel.x = floor( ptSel.x / m_dSnapStep + 0.5) * m_dSnapStep ;
       ptSel.y = floor( ptSel.y / m_dSnapStep + 0.5) * m_dSnapStep ;
    }
@@ -68,13 +68,42 @@ Scene::GetGridSnapPoint( int nSnap, const Point3d& ptWin, Point3d& ptSel)
    return true ;
 }
 
+//----------------------------------------------------------------------------
+bool
+Scene::GetGridSnapPointZ( bool bSketch, const Point3d& ptWin, const Point3d& ptGrid, Point3d& ptSel)
+{
+  // calcolo un punto e la direzione della linea di mira
+   Point3d ptLine ;
+   if ( ! UnProject( ptWin, ptLine))
+      return false ;
+   Vector3d vtLine = - m_vtDirCamera ;
+
+  // piano di elevazione :
+  // per il punto di griglia, contenente la perp. alla griglia e pił perp. possibile alla direzione di mira 
+   Vector3d vtNorm = vtLine - ( vtLine * m_frGrid.VersZ()) * m_frGrid.VersZ() ;
+   if ( ! vtNorm.Normalize())
+      return false ;
+
+  // determino l'intersezione della linea di mira con il piano di elevazione
+   double dDenom = vtLine * vtNorm ;
+   if ( fabs( dDenom) < COS_ORTO_ANG_SMALL)
+      return false ;
+   double dU = ( ( ptGrid - ptLine) * vtNorm) / dDenom ;
+   Point3d ptNear = ptLine + dU * vtLine ;
+
+  // proietto il punto sulla linea di elevazione
+   double dDeltaZ = ( ptNear - ptGrid) * m_frGrid.VersZ() ;
+   if ( ! bSketch)
+      dDeltaZ = floor( dDeltaZ / m_dSnapStep + 0.5) * m_dSnapStep ;
+   ptSel = ptGrid + dDeltaZ * m_frGrid.VersZ() ;
+
+   return true ;
+}
+
 //----------------------------------------------------------------------------
 bool
 Scene::GetSelectedSnapPoint( int nSnap, const Point3d& ptWin, int nW, int nH, Point3d& ptSel)
 {
-  // se Snap Sketch o Grid, devo trovare il punto sulla griglia
-   if ( nSnap == SP_SKETCH  ||  nSnap == SP_GRID)
-      return GetGridSnapPoint( nSnap, ptWin, ptSel) ;
   // verifico siano state selezionate delle entitą
    int nSel ;
    Select( ptWin, nW, nH, nSel) ;