Added an ivar for smallest radial angle distinguishable from polar

Change-Id: Ieb0a08623382788ac6bb52eebe753febec68fe3a

Hybrid/vtkPolarAxesActor.cxx

@@ -68,6 +68,7 @@ void vtkPolarAxesActor::PrintSelf( ostream& os, vtkIndent indent )
   os << indent << "Auto-Scale Radius" << this->AutoScaleRadius << endl;
   os << indent << "Minimum Angle" << this->MinimumAngle << endl;
   os << indent << "Maximum Angle" << this->MaximumAngle << endl;
+  os << indent << "Smallest Visible Polar Angle" << this->SmallestVisiblePolarAngle << endl;
   os << indent << "Radial Units (degrees): "
      << ( this->RadialUnits ? "On\n" : "Off\n" ) << endl;
 
@@ -144,6 +145,9 @@ vtkPolarAxesActor::vtkPolarAxesActor() : vtkActor()
   // Default maximum polar angle
   this->MaximumAngle = VTK_DEFAULT_MAXIMUM_POLAR_ANGLE;
 
+  // Default smallest radial angle distinguishable from polar axis
+  this->SmallestVisiblePolarAngle = .5;
+
   // By default show angle units (degrees)
   this->RadialUnits = true;
 
@@ -528,6 +532,12 @@ void vtkPolarAxesActor::BuildAxes( vtkViewport *viewport )
       { 
       // Prevent conflict between radial and polar axes titles
       axis->SetTitleVisibility( false );
+
+      if ( fabs( alpha ) < this->SmallestVisiblePolarAngle )
+        { 
+        // Do not show radial axes too close to polar axis
+        axis->SetAxisVisibility( false );
+        }
       }
     else
       {

Hybrid/vtkPolarAxesActor.h

@@ -110,6 +110,13 @@ public:
   vtkSetClampMacro( MaximumAngle, double, 0., 360. );
   vtkGetMacro( MaximumAngle, double );
 
+  // Description:
+  //  Set/Get the minimum radial angle distinguishable from polar axis
+  // NB: This is used only when polar axis is visible
+  // Default: 0.5
+  vtkSetClampMacro( SmallestVisiblePolarAngle, double, 0., 5. );
+  vtkGetMacro( SmallestVisiblePolarAngle, double );
+
   // Description: Set/Get whether angle units (degrees) are used to label radial axes 
   // Default: true
   vtkSetMacro( RadialUnits, bool ); 
@@ -308,6 +315,10 @@ protected:
   // Maximum polar angle
   double MaximumAngle;
 
+  // Description:
+  // Smallest radial angle distinguishable from polar axis
+  double SmallestVisiblePolarAngle;
+
   // Description:
   // Explicit actor bounds
   double Bounds[6];