[vtkusers] How to find specific point's normal....?

[David Doria]

On Thu, Apr 8, 2010 at 11:01 AM, renlishen <renlishen at gmail.com> wrote:
>
> David, thanks for your reply
> I'm using
> =============================================================================
> vtkFloatArray *PointNormalArray = vtkFloatArray::SafeDownCast(
> mCubes->GetOutput()->GetPointData()->GetNormals() ) ;
> float Normal2[ 8000 ] ;
> float *pTR = Normal2 ;
> for( int i = 0 ; i < PointNormalArray->GetNumberOfTuples() ; i++ )
>        {
>                PointNormalArray->GetTupleValue( i, pTR ) ;
>                pTR+=3 ;
>        }
> ===============================================================================
> to get normals.
> But I don't know how to assign the GetTupleValue to my point data set...
> I try to use point ID to find normal, but some error happen...
> My data set is
>        vtkImageData *ImageDataSrc = vtkImageData::New() ;
>        ImageDataSrc->SetDimensions(512, 512, 512) ;
>        ImageDataSrc->SetScalarType(VTK_UNSIGNED_CHAR) ;
>        ImageDataSrc->AllocateScalars() ;
>             .....
>             .....
> compute normal by
>        vtkMarchingCubes *mCubes = vtkMarchingCubes::New() ;
>        mCubes->SetInput( ImageDataSrc ) ;
>        mCubes->SetValue( 0, 100 ) ;
>        mCubes->ComputeNormalsOn() ;
>
> for example: if I want to know the point( 236,236,236 )'s normal...
> how can I get it~?
>
> thanks again...
>
> RenLi~

You can use the ComputePointId function to get the point ID:

int location[3] = {236,236,236};
vtkIdType id = mCubes->GetOutput()->ComputePointId(location);
PointNormalArray->GetTupleValue(id, pTR ) ;

Is that what you are looking for?

Thanks,

David