[vtk-developers] vtkGlyph3D & range clamping

[Will Schroeder]

John-

I apologize if I've missed something here: for which classes are you 
proposing these changes? vtkGlyph3D, vtkWarpScalar, and ?? How many classes 
are involved? Your ideas have merit but I'm wondering if it should be done 
class-by-class or somehow encapsulated in a helper class...

Will

At 06:20 PM 5/11/2005, John Platt wrote:
>Hi,
>
>Maybe I've missed something but I seem to spend a lot of time modifying 
>filters to normalise the input data at the time of execution. Here's an 
>example of bodging the scale factor so the warp is always shown a fixed size.
>
>void vtkWarpScalarEx::Execute()
>{
>     vtkDataArray* inScalars = 
> this->GetInput()->GetPointData()->GetScalars( this->InputScalarsSelection );
>     double scaleFactor = this->ScaleFactor;
>     if ( inScalars )
>       {
>       double maxNorm = inScalars->GetMaxNorm();
>       if ( maxNorm > 0.0 )
>         this->SetScaleFactor( scaleFactor/maxNorm );
>       }
>     vtkWarpScalar::Execute();
>     this->SetScaleFactor( scaleFactor );
>}
>
>Mapping attribute data to the range to [0,1] doesn't always solve the 
>problem either, particularly when computing a scale factor for sizing 
>glyphs. For example, suppose there are sphere glyphs representing masses 
>M1 < M2 and M2 is to be displayed a fixed size. Normalising scalars (say) 
>to [0, 1] will leave M1 zero size. Provision for this kind of 
>functionality requires independent access to the attribute data limits. 
>Here is a solution for the mass problem using UpperClampToMaxNormOn().
>
>vtkGlyph3D.h
>==========
>
>Replace
>
>   // Description:
>   // Specify range to map scalar values into.
>   vtkSetVector2Macro(Range,double);
>   vtkGetVectorMacro(Range,double,2);
>
>By
>
>   // Description:
>   // Specify the range for clamping the scalar values (or vector magnitude if
>   // ScaleByVector() is enabled). Scalars outside this range are set to the
>   // end points and then normalised to [0-1]. Glyphs for points with scalars
>   // less than or equal to Range[0] with therefore not be visible. This 
> range is
>   // only used with ClampingOn()
>   vtkSetVector2Macro(Range,double);
>   vtkGetVectorMacro(Range,double,2);
>
>   vtkSetMacro(LowerClampToMinNorm,int);
>   vtkBooleanMacro(LowerClampToMinNorm,int);
>   vtkGetMacro(LowerClampToMinNorm,int);
>
>   vtkSetMacro(UpperClampToMaxNorm,int);
>   vtkBooleanMacro(UpperClampToMaxNorm,int);
>   vtkGetMacro(UpperClampToMaxNorm,int);
>
>Insert
>
>   int LowerClampToMinNorm; // Use the min norm of the attribute data as 
> the lower clamp
>   int UpperClampToMaxNorm; // Use the max norm of the attribute data as 
> the upper clamp
>
>
>vtkGlyph3D.cxx (Revision: 1.112)
>========================
>
>vtkGlyph3D::vtkGlyph3D()
>
>Insert
>
>   this->LowerClampToMinNorm = 0;
>   this->UpperClampToMaxNorm = 0;
>
>vtkGlyph3D::Execute()
>
>Remove
>
>   // Check input for consistency
>   //
>   if ( (den = this->Range[1] - this->Range[0]) == 0.0 )
>     {
>     den = 1.0;
>     }
>
>After
>
>   else
>     {
>     haveVectors = 0;
>     }
>
>Insert
>
>   // Set the range for clamping the data scale factors.
>   if ( this->Clamping && ( this->LowerClampToMinNorm || 
> this->UpperClampToMaxNorm ) )
>     {
>     double* inRange = NULL;
>     if ( inScalars && this->ScaleMode == VTK_SCALE_BY_SCALAR )
>       {
>       inRange = inScalars->GetRange();
>       }
>     else if ( haveVectors )
>       {
>       if ( this->VectorMode == VTK_USE_NORMAL )
>         {
>         inRange = inNormals->GetRange( -1 );
>         }
>       else
>         {
>         inRange = inVectors->GetRange( -1 );
>         }
>       }
>     if ( inRange && LowerClampToMinNorm ) this->Range[0] = inRange[0];
>     if ( inRange && UpperClampToMaxNorm ) this->Range[1] = inRange[1];
>     }
>
>   if ( (den = this->Range[1] - this->Range[0]) == 0.0 ) den = 1.0;
>
>
>vtkGlyph3D::PrintSelf()
>
>Replace
>
>   os << indent << "Range: (" << this->Range[0] << ", " << this->Range[1] 
> << ")\n";
>
>By
>
>   os << indent << "Range: (";
>   this->LowerClampToMinNorm ? os << "Min norm,"   : os << this->Range[0] 
> << ",";
>   this->UpperClampToMaxNorm ? os << "Max norm)\n" : os << this->Range[1] 
> << ")\n";
>
>If this kind of functionality is useful I will add it to bug tracker as a 
>feature request.
>
>Where the clamping and normalisation are not combined, it would be useful 
>to have methods like
>
>             ScaleByMinNorm()/ScaleByMaxNorm()
>             SetLowerClamp( lower )/SetUpperClamp( upper )
>             MapToRange( lower, upper )
>
>Using MapToRange( 0, 1 ) on vtkMapper would allow scalars of any range to 
>be colour mapped red through blue without having to call SetRange() with 
>actual attribute values. This would go some way to lessening the 
>assumption that the data range is known in advance.
>
>Thanks for your consideration.
>
>John Platt.
>
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