[vtkusers] (Scalar)Data on PolyData

[Nils H. Busch]

Hello,

I have some questions regarding displaying (field)data on vtkPolyData in
vtk4.0 and would appreciate it, if someone could clarify some issues
regarding that.

Let me first briefly state what I am doing (or try to do, I should say):

In my vtk pipeline, I am reading one dataset from file, extract an
isocontour (via vtkMarchingCubes) from it, read a second (scalar)
dataset ("dataArray)"from file and try to map that onto a vtkPolyData
instance generated from vtkMarchingCubes with a statement like the
following:
vtkPolyData *output;
vtkDataArray *dataArray;
...
dataArray->SetName("SurfaceData");
...
output->GetPointData()->AddArray(dataArray);

Then, I render the pipeline with vtk and also write the polydata to file
(in OpenInventor format) with a class I have written myself).

I found this to work only in a way, I find not altogether obvious. Both,
rendering with a vtkPolyDataMapper and exporting to OpenInventor showed
the scalar data mapped onto the polydata, only if I specify the second
scalar data as

vtkPolyDataMapper *mapper = vtkPolyDataMapper::New();
mapper->SetScalarModeToUsePointFieldData();
mapper->ColorByArrayComponent("SurfaceData", 0);

Setting ScalarMode to use PointData or to Default did not work.
In my IO class, I use anagously something like:
vtkDataArray *scalars =
vtkAbstractMapper::GetScalars(pd,VTK_SCALAR_MODE_USE_POINT_FIELD_DATA,
0, 2, NULL, arrayComponent);

Why can't I specify the second dataset directly as point data (or how
would I have to do that correctly) ?
My second question concerns the 2 in the above statement.
If I add the surface data like above, the data array is added as the
third data array to my vtkPolyData instance. I am puzzled to why this is
so. Is this correct behaviour?
I really need to add the data array as the first data array in
vtkPolyData (below is a copy of the outcome of printing my vtkPolyData
instance to a stream to clarify what I mean).
BTW, what is supposed to be in the Scalars member ?
And the third question: what is the purpose of the Field Data member
(see below) and how can it be accessed?

I have tried to gather my code from various vtk examples and the vtk
sources, but I am not quite sure anymore what the correct and suggested
way of adding (scalar) data to poly data is for vtk4.0.

Thanks.

----------
ouput->PrintSelf(cout, 4); :

Debug: Off
    Modified Time: 1660
    Reference Count: 1
    Registered Events: (none)
    Source: 0x10031e90
    Release Data: Off
    Data Released: False
    Global Release Data: Off
    MaximumNumberOfPieces: -1
    PipelineMTime: 270
    UpdateTime: 1657
    UpdateExtent: Not Initialized
    Update Number Of Pieces: 1
    Update Piece: 0
    Update Ghost Level: 0
    RequestExactExtent: Off
     UpdateExtent: 0, 0, 0, 0, 0, 0
    WholeExtent: 0, -1, 0, -1, 0, -1
    Field Data:
      Debug: Off
      Modified Time: 258
      Reference Count: 1
      Registered Events: (none)
      Number Of Arrays: 0
      Number Of Components: 0
      Number Of Tuples: 0
    Locality: 0
    NumberOfConsumers: 0
    ExtentTranslator: (0x100320a0)
    MaximumNumberOfPieces: -1
    Number Of Points: 32608
    Number Of Cells: 63897
    Cell Data:
      Debug: Off
      Modified Time: 262
      Reference Count: 1
      Registered Events: (none)
      Number Of Arrays: 0
      Number Of Components: 0
      Number Of Tuples: 0
      Copy Flags: ( 1 1 1 1 1 )
      Scalars: (none)
      Vectors: (none)
      Normals: (none)
      TCoords: (none)
      Tensors: (none)
    Point Data:
      Debug: Off
      Modified Time: 1660
      Reference Count: 1
      Registered Events: (none)
      Number Of Arrays: 3
      Array 0 name = NULL
      Array 1 name = NULL
      Array 2 name = SurfaceData
      Number Of Components: 5
      Number Of Tuples: 32608
      Copy Flags: ( 1 1 1 1 1 )
      Scalars:
        Debug: Off
        Modified Time: 294
        Reference Count: 1
        Registered Events: (none)
        Name: (none)
        Number Of Components: 1
        Number Of Tuples: 32608
        Size: 32608
        MaxId: 32607
        LookupTable: (none)
        Array: 0x102e94a8
      Vectors: (none)
      Normals:
        Debug: Off
        Modified Time: 291
        Reference Count: 1
        Registered Events: (none)
        Name: (none)
        Number Of Components: 3
        Number Of Tuples: 32608
        Size: 97824
        MaxId: 97823
        LookupTable: (none)
        Array: 0x10249490
      TCoords: (none)
      Tensors: (none)
    Bounds:
      Xmin,Xmax: (24.875, 80)
      Ymin,Ymax: (31.9362, 174.25)
      Zmin,Zmax: (3.07692, 35)
    Compute Time: 1661
    Release Data: Off
    Number Of Points: 32608
    Point Coordinates: 0x100327b8
    Locator: 0x0
    Number Of Vertices: 0
    Number Of Lines: 0
    Number Of Polygons: 63897
    Number Of Triangle Strips: 0
    Number Of Pieces: 1
    Piece: 0
    Ghost Level: 0
    UpdateExtent: 0, 0, 0, 0, 0, 0
-----


--
    Nils H. Busch
    Max-Planck-Institute of Cognitive Neuroscience
    phone:  ++49 (341) 9940-035 fax:  ++49 (341) 9940-204
    e-mail: nilsb at cns.mpg.de