### Author:  [@TJ\_Corona](https://discourse.vtk.org/u/TJ_Corona)
#### Post date: [May 18, 2020, 3:36pm UTC](https://discourse.vtk.org/t/vtkm-reading-dataset-from-legacy-vtk-file/3285/8 "2020-05-18T15:36:34Z")
Can you confirm that the dataset from `reader->GetOutputAsDataSet()` contains a field “pointvar”? My guess is either the vtkm converter is not passing this array through correctly, or there is no array in the first place.
---
### Author:  [@McDave17](https://discourse.vtk.org/u/McDave17)
#### Post date: [May 19, 2020, 11:41am UTC](https://discourse.vtk.org/t/vtkm-reading-dataset-from-legacy-vtk-file/3285/9 "2020-05-19T11:41:45Z")
Actually, sadly i can’t. To be honest im not sure how to successfully render one of my Datasets using vtkm. The same Datasets were successfully used in VTK but I can’t manage to get it working in VTK-m.
I already successfully setup an OpenGL pane in my GUI and I am able to render to it.
In my old project I was using the MarchingCubes algorithm for example. I can’t even seem to include that in VTK-m, do you know if I have to enable a option in CMake while compiling VTK-m to eanble that filter?
---
### Author:  [@RobertMaynard](https://discourse.vtk.org/u/RobertMaynard)
#### Post date: [May 19, 2020, 1:31pm UTC](https://discourse.vtk.org/t/vtkm-reading-dataset-from-legacy-vtk-file/3285/10 "2020-05-19T13:31:14Z")
> [@McDave17](#):
>
> vtkmDataSet = tovtkm::Convert(reader-\>GetOutputAsDataSet());
The `tovtkm::Convert` function has two signatures. The single parameter version converts only point coordinates and topology, all fields are not converted. To convert fields you need to use the two
parameter version like this:
```auto
vtkmDataSet = tovtkm::Convert(reader->GetOutputAsDataSet(), tovtkm::FieldsFlag::PointsAndCells);
```
> [@McDave17](#):
>
> Actually, sadly i can’t. To be honest im not sure how to successfully render one of my Datasets using vtkm. The same Datasets were successfully used in VTK but I can’t manage to get it working in VTK-m.
An easy way to debug/see what is part of a `vtkm::cont::DataSet` is to use the `PrintSummary` method:
```auto
vtkmDataSet.PrintSummary(std::cout);
```
> [@McDave17](#):
>
> In my old project I was using the MarchingCubes algorithm for example. I can’t even seem to include that in VTK-m, do you know if I have to enable a option in CMake while compiling VTK-m to eanble that filter?
The VTK-m entry points for iso-contouring are `vtkm::filter::Contour` and `vtkm::worklet::Contour`. These classes will internally select an appropriate implementation such as MarchingCells or FlyingEdges based on the input data. It is not possible to explicitly call `MarchingCubes`
---
### Author:  [@McDave17](https://discourse.vtk.org/u/McDave17)
#### Post date: [May 19, 2020, 1:44pm UTC](https://discourse.vtk.org/t/vtkm-reading-dataset-from-legacy-vtk-file/3285/11 "2020-05-19T13:44:20Z")
> [@RobertMaynard](#):
>
> vtkmDataSet.PrintSummary(std::cout);
Thank you for your Help!
So this is the output of my program when I print the Dataset after I added the flags you suggested. How would I be able to determain how to create a contour over this?
```
MainWindow::onOpenMHDFile path=D:/Studium/Abschlussarbeit/raw/Lobster_u8_301_324_56_LE.mhd
DataSet:
CoordSystems[1]
Coordinate System coords assoc= Points valueType=class vtkm::Vec storageType=struct vtkm::cont::StorageTagVirtual numValues=5461344 bytes=65536128 [(0,0,0) (1,0,0) (2,0,0) ... (298,323,55) (299,323,55) (300,323,55)]
CellSet
StructuredCellSet:
UniformConnectivity<3> pointDim[301 324 56]
Fields[1]
MetaImage assoc= Points valueType=unsigned char storageType=struct vtkm::cont::StorageTagVirtual numValues=5461344 bytes=5461344 [0 0 0 ... 0 0 10]
```
---
### Author:  [@RobertMaynard](https://discourse.vtk.org/u/RobertMaynard)
#### Post date: [May 19, 2020, 1:50pm UTC](https://discourse.vtk.org/t/vtkm-reading-dataset-from-legacy-vtk-file/3285/12 "2020-05-19T13:50:14Z")
Your field name in VTK-m is `MetaImage` and not `pointvar`. Your original example should work with the correction for the field name.
---
### Author:  [@McDave17](https://discourse.vtk.org/u/McDave17)
#### Post date: [May 19, 2020, 2:05pm UTC](https://discourse.vtk.org/t/vtkm-reading-dataset-from-legacy-vtk-file/3285/13 "2020-05-19T14:05:12Z")
Thank you, finally making progress, sadly running into the next issue rather quickly. When I execute the contour I get some (to me) rather cryptic error messages and then a crash:
```
16:03:06.986 ( 17.858s) [main thread] TryExecute.cxx:55 ERR| TryExecute encountered an error: ErrorBadValue (Input array to worklet invocation the wrong size.)
16:03:06.989 ( 17.861s) [main thread] TryExecute.cxx:55 ERR| Failing functor: struct vtkm::worklet::internal::detail::DispatcherBaseTryExecuteFunctor
16:03:06.991 ( 17.863s) [main thread] TryExecute.cxx:55 ERR| Failing device: Serial
```
---
### Author:  [@RobertMaynard](https://discourse.vtk.org/u/RobertMaynard)
#### Post date: [May 20, 2020, 3:41pm UTC](https://discourse.vtk.org/t/vtkm-reading-dataset-from-legacy-vtk-file/3285/14 "2020-05-20T15:41:48Z")
> [@McDave17](#):
>
> Thank you, finally making progress, sadly running into the next issue rather quickly. When I execute the contour I get some (to me) rather cryptic error messages and then a crash:
The “Input array to worklet invocation the wrong size.” error message means that the `MetaImage` field length doesn’t match the number of points in the input data.
It sounds like the input data set being to VTK-m isn’t the exact same one as you read from disk, and therefore have a different number of points.
---
### Author:  [@McDave17](https://discourse.vtk.org/u/McDave17)
#### Post date: [June 1, 2020, 6:22pm UTC](https://discourse.vtk.org/t/vtkm-reading-dataset-from-legacy-vtk-file/3285/15 "2020-06-01T18:22:36Z")
Thank you, but how can I control that? Why would the transformation create a DataSet not equal to the one loaded? Or did I specify a wrong dimension size? Last isn’t likely, since the MetaImage is read fine in plain VTK.
---
### Author:  [@McDave17](https://discourse.vtk.org/u/McDave17)
#### Post date: [June 2, 2020, 11:53am UTC](https://discourse.vtk.org/t/vtkm-reading-dataset-from-legacy-vtk-file/3285/16 "2020-06-02T11:53:42Z")
Should the number of cells and the number of points be the same?
```
vtkmDataSet.GetNumberOfPoints()
```
returns 5 461 344 (=301 x 324 x 56, matches dimensions)
```
vtkmDataSet.GetNumberOfCells()
```
returns 5 329 500 (=300 x 323 x 55, shoudlnt this be smaller? More like dimenX - 2 instead dimenX - 1?)
This confuses me, I’d expect the number of cells be smaller than the number of points since the points on the edges are part of less cells.
---
### Author:  [@RobertMaynard](https://discourse.vtk.org/u/RobertMaynard)
#### Post date: [June 2, 2020, 12:20pm UTC](https://discourse.vtk.org/t/vtkm-reading-dataset-from-legacy-vtk-file/3285/17 "2020-06-02T12:20:44Z")
> More like dimenX - 2 instead dimenX - 1?
The number of cells is always Dim-1 compared to the points. The way I think about it is to imagine two connected cells. You have 3 points in the connected direction, and two cells.
---
### Author:  [@McDave17](https://discourse.vtk.org/u/McDave17)
#### Post date: [June 2, 2020, 12:33pm UTC](https://discourse.vtk.org/t/vtkm-reading-dataset-from-legacy-vtk-file/3285/18 "2020-06-02T12:33:15Z")
Okay. Then these values seem fine.
> [@RobertMaynard](#):
>
> It sounds like the input data set being to VTK-m isn’t the exact same one as you read from disk, and therefore have a different number of points.
Do you mean that the vtkMetaImageReader reads the data incorrectly? I.e. that the .mhd file ist not setup correclty? An therefore the Conversion is done correctly with an non functioning data set.
---
### Author:  [@McDave17](https://discourse.vtk.org/u/McDave17)
#### Post date: [June 2, 2020, 1:29pm UTC](https://discourse.vtk.org/t/vtkm-reading-dataset-from-legacy-vtk-file/3285/19 "2020-06-02T13:29:29Z")
This also makes me curios, why is the Coordinate System so massive? Is it supposed to be 65MB for 5.4 million 8 Byte values? Is the coordinatesystem to big for the actual MetaImage-Field?
```
DataSet:
CoordSystems[1]
Coordinate System coords assoc= Points valueType=class vtkm::Vec storageType=struct vtkm::cont::StorageTagVirtual numValues=5461344 bytes=65536128 [(0,0,0) (1,0,0) (2,0,0) ... (298,323,55) (299,323,55) (300,323,55)]
CellSet
StructuredCellSet:
UniformConnectivity<3> pointDim[301 324 56]
Fields[1]
MetaImage assoc= Points valueType=unsigned char storageType=struct vtkm::cont::StorageTagVirtual numValues=5461344 bytes=5461344 [0 0 0 ... 0 0 10]
MainWindow::onLeftRender
num cells=5329500, num fields=1, num points=5461344
```
---
### Author:  [@RobertMaynard](https://discourse.vtk.org/u/RobertMaynard)
#### Post date: [June 3, 2020, 12:29pm UTC](https://discourse.vtk.org/t/vtkm-reading-dataset-from-legacy-vtk-file/3285/20 "2020-06-03T12:29:51Z")
The coordinate system has 5461344 entries which is `= 301 x 324 x 56`. The 65MB datasize is correct if the coordinate system is being treated as a fully explicit ( each point is stored as an x,y,z coordinate ) instead of using an optimized layout.
The reason for the explicit coordinates is that the `tovtkm::Convert` function doesn’t currently have optimized paths for RectilinearGrids, and instead converts them into fully ExplictGrids.
[Next page](https://discourse.vtk.org/t/vtkm-reading-dataset-from-legacy-vtk-file/3285.md?page=2)